The LeanStorage Flutter SDK can be used to persist and query data in LeanCloud. The code below shows how you can create an object and store it into the cloud:
LCObject todo = LCObject("Todo");
todo["title"] = "R&D Weekly Meeting";
todo["content"] = "All team members, Tue 2pm";
await todo.save();
The SDK designed for each language interacts with the same REST API via HTTPS, offering fully functional interfaces for you to manipulate the data in the cloud.
Storing data on LeanCloud is built around LCObject. Each LCObject contains key-value pairs of JSON-compatible data. This data is schema-free, which means that you don't need to specify ahead of time what keys exist on each LCObject. Simply set whatever key-value pairs you want, and our backend will store it.
For example, the LCObject storing a simple todo item may contain the following data:
title: "Email Linda to Confirm Appointment",
isComplete: false,
priority: 2,
tags: ["work", "sales"]
Data Types
LCObject supports a wide range of data types to be used for each field, including common ones like String, Number, Boolean, Object, Array, and Date. You can nest objects in JSON format to store more structured data within a single Object or Array field.
Special data types supported by LCObject include Pointer and File, which are used to store a reference to another LCObject and binary data respectively.
LCObject also supports GeoPoint, a special data type you can use to store location-based data. See GeoPoints for more details.
We do not recommend storing large pieces of binary data like images or documents with LCObject. The size of each LCObject should not exceed 128 kilobytes. We recommend using LCFile for storing images, documents, and other types of files. To do so, create LCFile objects and assign them to fields of LCObject. See Files for details.
Keep in mind that our backend stores dates in UTC format and the SDK will convert them to local times upon retrieval.
The date values displayed in your app's Dashboard > LeanStorage > Data are also converted to match your operating system's time zone. The only exception is that when you retrieve these date values through our REST API, they will remain in UTC format. You can manually convert them using appropriate time zones when necessary.
To learn about how you can protect the data stored on LeanCloud, see Data and Security.
Creating Objects
The code below creates a new instance of LCObject with class Todo:
LCObject todo = LCObject('Todo');
The constructor takes a class name as a parameter so that the cloud knows the class you are using to create the object. A class in LeanCloud is comparable to a table in a relational database. A class name starts with a letter and can only contain numbers, letters, and underscores.
Saving Objects
The following code saves a new object with class Todo to the cloud:
LCObject todo = LCObject("Todo");
todo['title'] = 'Sign up for Marathon';
todo['priority'] = 2;
await todo.save();
To make sure the object is successfully saved, take a look at Dashboard > LeanStorage > Data > Todo in your app. You should see a new entry of data with something like this when you click on its objectId:
You don't have to create or set up a new class called Todo in Dashboard > LeanStorage > Data before running the code above. If the class doesn't exist, it will be automatically created.
There are several built-in fields that are provided by default which you don't need to specify in your code:
Built-in Field
Type
Description
objectId
String
A unique identifier for each saved object.
ACL
LCACL
Access Control List, a special object defining the read and write permissions of other people.
createdAt
DateTime
The time the object was created.
updatedAt
DateTime
The time the object was last modified.
Each of these fields is filled in by the cloud automatically and doesn't exist on the local LCObject until a save operation has been completed.
Field names, or keys, can only contain letters, numbers, and underscores. A custom key can neither start with double underscores __, nor be identical to any system reserved words or built-in field names (ACL, className, createdAt, objectId, and updatedAt) regardless of letter cases.
Values can be strings, numbers, booleans, or even arrays and dictionaries — anything that can be JSON-encoded. See Data Types for more information.
We recommend that you adopt CamelCase naming convention to NameYourClassesLikeThis and nameYourKeysLikeThis, which keeps your code more readable.
Retrieving Objects
If LCObject is already in the cloud, you can retrieve it using its objectId with the following code:
LCQuery<LCObject> query = LCQuery('Todo');
LCObject todo = await query.get('582570f38ac247004f39c24b');
String title = todo['title'];
int priority = todo['priority'];
String objectId = todo.objectId;
DateTime updatedAt = todo.updatedAt;
DateTime createdAt = todo.createdAt;
If you try to access a field or property that doesn't exist, the SDK will not raise an error. Instead, it will return .
LCObject todo = LCObject.createWithoutData('Todo', '582570f38ac247004f39c24b');
await todo.fetch();
// todo is refreshed
LCObject todo = LCObject.createWithoutData('Todo', '582570f38ac247004f39c24b');
await todo.fetch(includes: ['priority','location']);
// Only priority and location will be retrieved and refreshed
Updating Objects
To update an existing object, assign the new data to each field and call the save method. For example:
LCObject todo = LCObject.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo['content'] = 'Weekly meeting has been rescheduled to Wed 3pm for this week.';
await todo.save();
LeanCloud automatically figures out which data has changed and only the fields with changes will be sent to the cloud. The fields you didn't update will remain intact.
try {
LCObject account = LCObject.createWithoutData('Account', '5745557f71cfe40068c6abe0');
// Atomically decrease balance by 100
int amount = -100;
account.increment('balance', amount);
// Add the condition
LCQuery<LCObject> query = LCQuery('Account');
query.whereGreaterThanOrEqualTo('balance', -amount);
// Return the latest data in the cloud upon completion.
// All the fields will be returned if the object is new,
// otherwise only fields with changes will be returned.
await account.save(fetchWhenSave: true, query: query);
print('Balance: ${account['balance']}');
} on LCException catch (e) {
if (e.code == 305) {
print("Insufficient balance. Operation failed!");
}
}
Updating Counters
Take Twitter as an example, we need to keep track of how many Likes and Retweets a tweet has gained so far. Since a Like or Retweet action can be triggered simultaneously by multiple clients, saving objects with updated values directly can lead to inaccurate results. To make sure that the total number is stored correctly, LeanCloud allows you to atomically increase (or decrease) the value of a number field:
post.increment('likes',1);
You can specify the amount of increment (or decrement) by providing an additional argument. If the argument is not provided, 1 is used by default.
Updating Arrays
There are several operations that can be used to atomically update an array associated with a given key:
add(key, value) appends the given object to the end of an array.
addAll(key, values) appends the given objects to the end of an array.
addUnique(key, value) adds the given object into an array only if it is not in it. The object will be inserted at a random position.
addAllUnique(key, values) appends the given array objects to the end of an array ensuring that each object only appears once within the array.
remove(key, value) removes all instances of the given object from an array.
removeAll(key, values) removes all instances of the given objects from an array.
For example, Todo has a field named alarms for keeping track of times at which a user wants to be alerted. The following code adds the times to the alarms field:
The following code deletes a Todo object from the cloud:
LCObject todo = LCObject.createWithoutData('Todo', '582570f38ac247004f39c24b');
await todo.delete();
You can delete a given field of an object with the unset method:
LCObject todo = LCObject.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo.unset('priority');
await todo.save();
Removing data from the cloud should always be dealt with great caution as it may lead to non-recoverable data loss. We strongly advise that you read ACL Guide to understand the risks thoroughly. You should also consider implementing class-level, object-level, and field-level permissions for your classes in the cloud to guard against unauthorized data operations.
Batch Processing
You can create, save, delete, or fetch multiple objects within a single request:
The following code sets isComplete of all Todo objects to be true:
LCQuery<LCObject> query = LCQuery('Todo');
List<LCObject> results = await query.find();
for (LCObject todo in results) {
todo['isComplete'] = true;
}
await LCObject.saveAll(results);
Although each function call sends multiple operations in one single network request, saving operations and fetching operations are billed as separate API calls for each object in the collection, while deleting operations are billed as a single API call.
Data Models
Objects may have relationships with other objects. For example, in a blogging application, a Post object may have relationships with many Comment objects. LeanCloud supports three kinds of relationships, including one-to-one, one-to-many, and many-to-many.
One-to-One and One-to-Many Relationships
One-to-one and one-to-many relationships are modeled by saving LCObject as a value in the other object. For example, each Comment in a blogging app might correspond to one Post.
The following code creates a new Post with a single Comment:
// Create a post
LCObject post = LCObject("Post");
post['title'] = 'I am starving!';
post['content'] = 'Hmmm, where should I go for lunch?';
// Create a comment
LCObject comment = LCObject("Comment");
comment['content'] = 'KFC is the best!';
// Add the post as a property of the comment
comment['parent'] = post;
// This will save both post and comment
await comment.save();
Internally, the backend will store the referred-to object with the Pointer type in just one place in order to maintain consistency. You can also link objects using their objectIds like this:
LCObject post = LCObject.createWithoutData('Post', '57328ca079bc44005c2472d0');
comment['post'] = post;
See Relational Queries for instructions on how to query relational data.
Many-to-Many Relationships
The easiest way to model many-to-many relationships is to use arrays. In most cases, using arrays helps you reduce the number of queries you need to make and leads to better performance. However, if additional properties need to be attached to the relationships between two classes, using join tables would be a better choice. Keep in mind that the additional properties are used to describe the relationships between classes rather than any single class.
We recommend you to use join tables if the total amount of objects of any class exceeds 100.
Modeling relationships among data could be a tough job. We have written a dedicated article to address Data Modeling in greater detail, which we highly recommend you to read.
Queries
We've already seen how you can retrieve a single object from the cloud with LCObject, but it doesn't seem to be powerful enough when you need to retrieve multiple objects that match certain conditions at once. In such situation, LCQuery would be a more efficient tool you can use.
Basic Queries
The general steps of performing a basic query include:
Creating LCQuery.
Putting conditions on it.
Retrieving an array of objects matching the conditions.
The code below retrieves all Student objects whose lastName is Smith:
LCQuery<LCObject> query = LCQuery('Student');
query.whereEqualTo('lastName', 'Smith');
// students is an array of Student objects satisfying conditions
List<LCObject> students = await query.find();
You can apply multiple constraints to a single query, and objects will only be in the results if they match all of the constraints. In other words, it's like concatenating constraints with AND:
You can limit the number of results by setting limit (defaults to 100):
query.limit(10);
For performance reasons, the maximum value allowed for limit is 1000, meaning that LeanCloud would only return 1,000 results even it is set to be greater than 1000.
If you need exactly one result, you may use first for convenience:
Keep in mind that the higher the skip goes, the slower the query will run. You may consider using createdAt or updatedAt (which are indexed) to set range boundaries for large datasets to make queries more efficient.
For sortable types, you can control the order in which results are returned:
You can restrict the fields returned by providing a list of keys with . The code below retrieves todos with only the title and content fields (and also special built-in fields such as objectId, createdAt, and updatedAt):
You can add a minus prefix to the attribute name for inverted selection.
For example, if you do not care about the post author, use -author.
The inverted selection also applies to preserved attributes, and can be used with dot notations, e.g. -pubUser.createdAt.
Queries on String Values
Use to restrict to string values that start with a particular string. Similar to a LIKE operator in SQL, it is indexed so it is efficient for large datasets:
LCQuery<LCObject> query = new LCQuery('Todo');
// SQL equivalent: title LIKE 'lunch%'
query.whereStartsWith('title', 'lunch');
Use to restrict to string values that contain a particular string:
LCQuery<LCObject> query = LCQuery('Todo');
// SQL equivalent: title LIKE '%lunch%'
query.whereContains('title', 'lunch');
Unlike whereStartsWith, whereContains can't take advantage of indexes, which is not encouraged to be used for large datasets.
Please note that both whereStartsWith and whereContains perform case-sensitive matching, so the examples above will not look for string values containing Lunch, LUNCH, etc.
If you are looking for string values that do not contain a particular string, use whereMatches with regular expressions:
However, performing queries with regular expressions as constraints can be very expensive, especially for classes with over 100,000 records. The reason behind this is that queries like this can't take advantage of indexes and will lead to exhaustive scanning of the whole dataset to find the matching objects. We recommend that you take a look at our In-App Searching feature, a full-text search solution we provide to improve your app's searching ability and user experience.
If you are facing performance issues with queries, please refer to Optimizing Performance for possible workarounds and best practices.
Queries on Array Values
The code below looks for all the objects with work as an element of its array field tags:
query.whereEqualTo('tags', 'work');
To look for objects whose array field tags contains three elements:
query.whereSizeEqualTo('tags', 3);
You can also look for objects whose array field tags contains work, sales, andappointment:
To retrieve objects whose field matches any one of the values in a given list, you can use instead of performing multiple queries. The code below constructs a query that retrieves todo items with priority to be 1or2:
Conversely, you can use whereNotContainedIn if you want to retrieve objects that do not match any of the values in a list.
Relational Queries
There are several ways to perform queries for relational data. To retrieve objects whose given field matches a particular LCObject, you can use just like how you use it for other data types. For example, if each Comment has a Post object in its post field, you can fetch all the comments for a particular Post with the following code:
To retrieve objects whose given field contains LCObject that matches a different query, you can use . The code below constructs a query that looks for all the comments for posts with images:
To retrieve objects whose given field does not contain LCObject that matches a different query, use whereDoesNotMatchQuery instead.
Sometimes you may need to look for related objects from different classes without extra queries. In such situations, you can use include on the same query. The following code retrieves the last 10 comments together with the posts related to them:
LCQuery<LCObject> query = LCQuery('Comment');
query.orderByDescending('createdAt');
query.limit(10);
// Include the related post together with each comment
query.include('post');
// comments contains the last 10 comments including the post associated with each
List<LCObject> comments = await query.find();
for (LCObject comment in comments) {
// This does not require a network access
LCObject post = comment['post'];
}
You can even indicate multi-level associations using dot notations. If you wanted to include the post for each comment as well as the author of the post, you can do:
query.include('post.author');
Feel free to use as many times as you need for the same query to have multiple fields included. Related objects retrieved in this way also works with `LCQuery` helpers like.
Multi-level conditions passed into .include won't work with any LCObject contained in an array field. The furthest level that can be reached is the field itself.
You can also use dot notations with .select to limit the fields returned from the related objects:
query.select('post.author.firstName');
Caveats about Inner Queries
The backend of LeanCloud is not built on relational databases, which makes it impossible to join tables while querying. For the relational queries mentioned above, what LeanCloud would do is to perform an inner query first (with 100 as default limit and 1000 as maximum) and then insert the result from this query into the outer query. If the number of records matching the inner query exceeds the limit and the outer query contains other constraints, the amount of the records returned in the end could be zero or less than your expectation since only the records within the limit would be inserted into the outer query.
The following actions can be taken to solve the problem:
Make sure the number of records in the result of the inner query is no more than 100. If it is between 100 and 1,000, set 1000 as the limit of the inner query.
Create redundancy for the fields being queried by the inner query on the table for the outer query.
Repeat the same query with different skip values until all the records are gone through (performance issue could occur if the value of skip gets too big).
Counting Objects
If you just need to count how many objects match a query but do not need to retrieve the actual objects, use instead of. For example, to count how many todos have been completed:
LCQuery<LCObject> query = LCQuery('Todo');
query.whereEqualTo('isComplete', true);
int count = await query.count();
print('$count todos completed.');
Compound Queries
Compound queries can be used if complex query conditions need to be specified. A compound query is a logical combination (OR or AND) of subqueries.
Note that we do not support GeoPoint or non-filtering constraints (e.g. near, withinGeoBox, limit, skip, ascending, descending, include) in the subqueries of a compound query.
OR-ed Query Constraints
An object will be returned as long as it fulfills any one of the subqueries. The code below constructs a query that looks for all the todos that either have priorities higher than or equal to 3, or are already completed:
Queries regarding GeoPoint cannot be present among OR-ed queries.
AND-ed Query Constraints
The effect of using AND-ed query is the same as adding constraints to LCQuery. The code below constructs a query that looks for all the todos that are created between 2016-11-13 and 2016-12-02:
While using an AND-ed query by itself doesn't bring anything new comparing to a basic query, to combine two or more OR-ed queries, you have to use AND-ed queries:
There are several factors that could lead to potential performance issues when you conduct a query, especially when more than 100,000 records are returned at a time. We are listing some common ones here so you can design your apps accordingly to avoid them:
Querying with "not equal to" or "not include" (index will not work)
Querying on strings with a wildcard at the beginning of the pattern (index will not work)
Using count with conditions (all the entries will be gone through)
Using skip for a large number of entries (all the entries that need to be skipped will be gone through)
Sorting without index (querying and sorting cannot share a composite index unless the conditions used on them are both covered by the same one)
Querying without index (the conditions used on the query cannot share a composite index unless all of them are covered by the same one; additional time will be consumed if excessive data falls under the uncovered conditions)
Files
LCFile allows you to store application files in the cloud that would otherwise be too large or cumbersome to fit into a regular LCObject. The most common use case is storing images, but you can also use it for documents, videos, music, and any other binary data.
When creating files from URLs, the SDK will not upload the actual files into the cloud but will store the addresses of the files as strings. This will not lead to actual traffic for uploading files, as opposed to creating files in other ways by doing which the files will be actually stored into the cloud.
LeanCloud will auto-detect the type of the file you are uploading based on the file extension, but you can also specify the Content-Type (commonly referred to as MIME type):
The file we uploaded here is named avatar.jpg. There are a couple of things to note here:
Each file uploaded will get its unique objectId, so it is allowed for multiple files to share the same name.
A correct extension needs to be assigned to each file which the cloud will use to infer the type of a file. For example, if you are storing a PNG image with LCFile, use .png as its extension.
If the file doesn't have an extension and the content type is not specified, LeanCloud defaults the file's type to be application/octet-stream.
Saving Files
By saving a file, you store it into the cloud and get a permanent URL pointing to it:
await file.save();
print(file.objectId);
A file successfully uploaded can be found in the _File class and cannot be modified later. If you need to change the file, you have to upload the modified file again and a new objectId and URL will be generated.
You can associate a file with LCObject after it is saved:
Note that the url field of internal files (files uploaded to LeanCloud file service) is dynamically generated by the cloud, which will switch custom domain names automatically.
Therefore, querying files by the url field is only applicable to external files (files created by saving the external URL directly to the _File table).
Query internal files by the key field (path in URL) instead.
On a related note, if the files are referenced in an array field of LCObject and you want to get them within the same query for LCObject, you need to use the method with LCQuery. For example, if you are retrieving all the todos with the same title Get Cakes and you want to retrieve their related attachments at the same time:
// Get all todos with the same title and contain attachments
LCQuery<LCObject> query = LCQuery('Todo');
query.whereEqualTo('title', 'Get Cakes');
query.whereExists('attachments');
query.include('attachments');
List<LCObject> todos = await query.find();
for (LCObject todo in todos) {
// Include attachments with each todo
List<LCObject> attachments = todo['attachments'];
}
Upload Progress
You can monitor the progress of uploading and display that to the user:
await file.save(onProgress: (int count, int total) {
print('$count/$total');
if (count == total) {
print('done');
}
});
File Metadata
When uploading a file, you can attach additional properties to it with metaData. A file's metaData cannot be updated once the file is stored to the cloud.
By default, a file is not allowed to be deleted. You can change the setting by going to Dashboard > LeanStorage > Data > _File and select Others > Permission settings > delete.
CDN Support
You can set up your own CDN to improve the speed your users access the files stored on LeanCloud. Take Amazon CloudFront CDN as an example:
Take the domain name from the URL of your LCFile and fill it into CloudFront's Origin Domain Name. Leave the other settings with defaults.
GeoPoints
LeanCloud allows you to associate real-world latitude and longitude coordinates with an object by adding LCGeoPoint to the LCObject. By doing so, queries on the proximity of an object to a given point can be performed, allowing you to implement functions like looking for users or places nearby easily.
To associate a point with an object, you need to create the point first. The code below creates LCGeoPoint with 39.9 as latitude and 116.4 as longitude:
LCGeoPoint point = LCGeoPoint(39.9, 116.4);
Now you can store the point in an object as a regular field:
todo['location'] = point;
Geo Queries
With a number of existing objects with spatial coordinates, you can find out which of them are closest to a given point, or are contained within a particular area. This can be done by adding another restriction to LCQuery using . The code below returns a list of Todo objects with location closest to a given point:
LCQuery<LCObject> query = LCQuery('Todo');
LCGeoPoint point = LCGeoPoint(39.9, 116.4);
query.whereNear('location', point);
query.limit(10);
List<LCObject> todos = await query.find();
Additional sorting conditions like orderByAscending and orderByDescending will gain higher priorities than the default order by distance.
To have the results limited within a certain distance, check out in our API docs.
You can also query for the set of objects that are contained within a rectangular bounding box with whereWithinGeoBox:
Each LCObject may only have one field containing LCGeoPoint object.
Points should not exceed the extreme ends of the ranges. Latitude should be between -90.0 and 90.0. Longitude should be between -180.0 and 180.0. Attempting to set latitude or longitude out of bounds will cause an error.
Users
At the core of many apps, there is a notion of user accounts that allows users to access their information in a secure manner. We provide a specialized user class called LCUser which automatically handles much of the functionality required for user account management in your app.
LCUser is a subclass of LCObject. Therefore, all the methods that work for LCObject also work for LCUser. The only difference is that LCUser has some additional features specific to user accounts. Each app has a dedicated _User class for storing LCUser.
User Properties
LCUser offers the following fields that LCObject does not have:
username: The username of the user.
password: The password of the user.
email: The email address of the user.
emailVerified: Whether the user has verified the email address with LeanCloud or not.
mobilePhoneNumber: The mobile phone number of the user.
mobilePhoneVerified: Whether the user has verified the mobile phone number with LeanCloud or not.
We'll go through each of these in detail as we run through the various use cases for users.
Signing up
When a user first opens your app, you may want them to sign up for an account. The following code shows a typical sign-up process with username and password:
// Create an instance
LCUser user = LCUser();
// Same as user['username'] = 'Tom';
user.username = 'Tom';
user.password = 'cat!@#123';
// Optional
user.email = 'tom@leancloud.rocks';
user.mobile = '+19490008888';
// Other fields can be set in the same way as LCObject
user['gender'] = 'secret';
await user.signUp();
A new LCUser should always be created using signUp rather than save. Subsequent updates to a user can be done with .
If the code returns the error 202, it means that a user with the same username already exists in _User table and the client should prompt the user to try a different username. It is also required that each email or mobilePhoneNumber appears only once in the corresponding column. Otherwise, error 203 or 214 will occur. You may ask a user to sign up with an email address and make the username to be the same as the email. By doing so, the user can directly reset their password with email.
When creating a user with username and password, the SDK sends the password to the cloud in plaintext through HTTPS and the password will be hashed once it arrives to the cloud. (The cloud has no restrictions on password length and complexity.) We never store passwords in plaintext, nor will we ever transmit passwords back to the client in plaintext. Our hashing algorithm guarantees that the original password cannot be retrieved by rainbow table attack and even app developers themselves will not be able to see the password. Keep in mind that the password should not be hashed by the client, or the password reset function will not work.
Signing up with Phones
For a mobile app, it's also common to ask users to sign up with their phone numbers instead of usernames and passwords. There are two basic steps in it. First, ask the user to enter a phone number that can receive text messages. When the user clicks on the "Get Verification Code" button, call the following method to have a 6-digit verification code sent to the phone number the user just entered:
await LCSMSClient.requestSMSCode('+19490008888');
After the verification code is entered by the user, call the following method to finish signing up:
The username will be the same as mobilePhoneNumber and a password will be generated by LeanCloud automatically.
If you wish to let the user specify their own password, you can let them fill in a password together with their mobile phone number, and then follow the process of registering with username and password described in the previous section,
submitting the user's mobile phone number as the value of both the username and the mobilePhoneNumber fields.
If you wish, you can also check the following options in "Dashboard > LeanStorage > Users > Settings": "Do not allow users with unverified phone numbers to log in", and/or "Allow users with verified phone numbers to login with SMS".
Phone Number Format
A phone number that LCUser accepts should have a leading plus sign (+) immediately followed by the country code and the phone number without any dashes, spaces, or other non-numeric characters. For instance, +8618200008888 is a valid China number (86 is the country code) and +19490008888 is a valid US or Canada number (1 is the country code).
For a list of countries and regions that LeanCloud can reach out through SMS, please refer to the Pricing page on our website.
Logging in
The code below logs a user in with username and password:
try {
// success
LCUser user = await LCUser.login('Tom', 'cat!@#123');
} on LCException catch (e) {
// failure (probably due to password error)
print('${e.code} : ${e.message}');
}
Logging in with Emails
The code below logs a user in with email and password:
try {
LCUser user = await LCUser.loginByEmail('tom@leancloud.rocks', 'cat!@#123');
} on LCException catch (e) {
print('${e.code} : ${e.message}');
}
Logging in with Phones
If you are allowing users to sign up with their phone numbers, you can also let them log in with either a password or a verification code sent via text message. The code below logs a user in with phone number and password:
try {
LCUser user = await LCUser.loginByMobilePhoneNumber('+19490008888', 'cat!@#123');
} on LCException catch (e) {
print('${e.code} : ${e.message}');
}
By default, LeanCloud allows a user to log in to their account as long as the phone number and the password are correct even when the ownership of the phone hasn't been verified. To make your app more secure, you can choose to allow only those who have their phones verified to log in. The option can be found in Dashboard > LeanStorage > Settings.
You may also let a user in with a verification code sent to their phone, which is useful when the user forgets the password and does not want to reset it at the moment. Similar to the steps of signing a user up with phone numbers, ask the user to enter the phone number associated with the account, and call the following method once the user clicks on the "Get Verification Code" button:
await LCUser.requestLoginSMSCode('+19490008888');
After the verification code is entered by the user, call the following method to finish logging in:
During the development of your application, you may need to test the sign-up or log-in related API intensively with your phone. As there are, however, limits to how quickly messages can be sent into the carrier networks, your testing pace can be significantly affected.
To work around it, you can set up a sandbox phone number in Dashboard > Messaging > SMS > Settings. LeanCloud will issue a fixed verification code to go with that sandbox phone number. Whenever LeanCloud detects such combination of data, the user will be let right in authenticated without any connections to the carrier networks being made.
On a related note, a sandbox phone number also comes in handy for iOS apps that allow users to log in with SMS code. This is because Apple may ask developers to provide a fixed combination of phone number and verification code for them to review the app as a normal user. Failure to do so may result in their app being rejected by the App Store.
For more details regarding the limitations of sending and receiving SMS messages, see SMS Guide.
Single Device Sign-on
In some scenarios you may want to restrict a user's account to be logged on by no more than one device at a time. That is, when a user logs in to the app on a new device, all the previous sessions on other devices will become invalid. Here's the instruction about how you can implement this feature with LeanCloud:
Create a new class that keeps track of each user's credentials and device information.
Each time when a user logs in on a device, update the device information of this user to be the current device.
When the app running on another device is opened, check if the device matches the one stored in the cloud. If it does not, log the user out.
User Account Lockout
If the wrong password or verification code is entered for an account for more than 6 times within 15 minutes, the account will be disabled temporarily and the error { "code": 1, "error": "You have exceeded the maximum number of login attempts, please try again later, or consider resetting your password." } will be returned.
The account will be automatically recovered 15 minutes after the last attempt and the process cannot be expedited through SDK or REST API. While the account is disabled, the user cannot be logged in even though the correct credentials are provided. The restriction applies to both client-side SDKs and LeanEngine.
Verifying Emails
You can request that your users have their email addresses verified before they can log in or access certain functions in your app. This makes it harder for spam users to abuse your app. By default, each user has an emailVerified field which becomes false when the user first signs up or has their email address changed. In your app's Dashboard > LeanStorage > Settings, you can enable Send verification emails when users register or change email addresses from clients so that when a user signs up or changes their email address, an email containing a verification link will be sent out automatically. You can find the option to prevent users with unverified email addresses from logging in on the same page.
If a user forgets to click on the link and needs to have their account verified later, the following code can be used to send a new email:
The emailVerified will become true after the link is clicked on. This field can never be true when the email field is empty.
Verifying Phone Numbers
Similar to Verifying Emails, you can also request that your users have their phone numbers verified before they can log in or access certain functions in your app. By default, each user has a mobilePhoneVerified field which becomes false when the user first signs up or has their phone number changed.
In your app's Dashboard > LeanStorage > User > Setting, you can find the option to prevent users with unverified phone numbers from logging in on the same page.
You can also initiate a verification request at anytime with the following code:
LeanCloud also supports verifying the number before a user binds or updates a number.
await LCUser.requestSMSCodeForUpdatingPhoneNumber('+19490008888');
await LCUser.verifyCodeForUpdatingPhoneNumber('+19490008888', '123456');
// update local data
LCUser currentUser = await LCUser.getCurrent();
user.mobile = '+19490008888';
Current User
After a user is logged in, LeanCloud SDK automatically stores the session information of this user in the client so that the user does not need to log in each time they open the client. The following code checks if there is a user logged in:
LCUser currentUser = await LCUser.getCurrent();
if (currentUser != null) {
// Redirect to the home page
} else {
// Show the sign-up or log-in page
}
The session information of a user will remain in the client until the user is logged out:
A session token will be returned to the client after a user is logged in. It will be cached by our SDK and will be used for authenticating requests made by the same LCUser in the future. The session token will be included in the header of each HTTP request made from the client, which helps the cloud identify the LCUser sending the request.
Below are the situations when you may need to log a user in with session token:
A session token is already cached on the client which can be used to automatically log the user in (you can use to get the session token of the current user).
A WebView within the app needs to know the current user.
The user is logged in on the server side using your own authentication routines and the server is able to provide the session token to the client.
The code below logs a user in with session token (the session token will be validated before proceeding):
For security reasons, please avoid passing session tokens as a part of URLs in non-private environments. This increases the risk that they will be captured by attackers.
If Log out the user when password is updated is checked on in Dashboard > LeanStorage > Settings, the session token of a user will be reset in the cloud after this user changes the password and the client needs to prompt the user to log in again. Otherwise, 403 (Forbidden) will be returned as an error.
The code below checks if a session token is valid:
The code above will check if there is a user in the _User table that has the email to be the same as the one provided and will send them a password reset email if so. As mentioned previously, you can make the username of each user to be the same as their email, or collect the email separately and store it in the email field.
The content of the password reset email is fully customizable. You can go to your app's Dashboard > Settings > Email templates and modify the corresponding template.
Alternatively, you can ask for the mobile phone number instead of the email to reset their password:
The user enters the mobile phone number used for the account.
LeanCloud sends a short message to the number including a verification code.
The user types in the verification code and a new password.
The code below sends a verification code to a number:
The code above will check if there is a user in the _User table that has the mobilePhoneNumber to be the same as the one provided and will send them a verification code if so.
By changing the settings in Dashboard > LeanStorage > Settings, you can restrict the use of the mobile phone number for the above flow only if the mobilePhoneVerified field is true.
The code below resets the password of a user after they enter the verification code and a new password:
To query for users, you can simple create a new LCQuery for _User:
LCQuery<LCUser> userQuery = LCUser.getQuery();
For security reasons, the _User table of each new app has its find permission disabled by default. Each user can only access their own data in _User table and cannot access that of others. If you need to allow each user to view other users' data, we recommend that you create a new table to store such data and enable the find permission of this table. You may also encapsulate queries on users within LeanEngine and avoid opening up find permissions of _User tables.
See Security of User Objects for other restrictions applied to the _User table, and Data and Security for more information regarding class-level permission settings.
Associations
Associations involving LCUser works in the same way as basic LCObject. The code below saves a new book for an author and retrieves all the books written by that author:
The LCUser class is secured by default. You are not able to invoke any save- or delete-related methods unless the LCUser was obtained using an authenticated method like or. This ensures that each user can only update their own data.
The reason behind this is that most data stored in LCUser can be very personal and sensitive, such as mobile phone number, social network account ID, etc. Even the app's owner should avoid tampering with these data for the sake of user's privacy.
The code below illustrates this security policy:
try {
LCUser user = await LCUser.login('Tom', 'cat!@#123');
// Attempt to change username
user['username'] = 'Jerry';
// Password is hashed and an empty string will be returned
String password = user['password'];
// This will work since the user is authenticated
await user.save();
// Get the user with a non-authenticated method
LCQuery<LCUser> userQuery = LCQuery('_User');
LCUser unauthenticatedUser = await userQuery.get(user.objectId);
unauthenticatedUser['username'] = 'Toodle';
// This will not succeed since the user is unauthenticated
unauthenticatedUser.save();
} on LCException catch (e) {
print('${e.code} : ${e.message}');
}
The LCUser obtained from LCUser.getCurrent() will always be authenticated.
To check if LCUser is authenticated, you can invoke the method. You do not need to check if LCUser is authenticated if it is obtained via an authenticated method.
As a reminder, the user's password can be set when signing up but cannot be modified and saved to the cloud afterward unless the user requests it to be reset. It will not be cached on the client and will show as null when being retrieved from the cloud after the user is logged in.
Security of Other Objects
For each given object, you can specify which users are allowed to read it and which are allowed to modify it. To support this type of security, each object has an access control list, implemented by the class. More details can be found in ACL Guide.
Linking Users
LeanCloud allows you to link your users with services like GitHub, Twitter, and Facebook (commonly known as social networking services, or SNS), allowing your users to sign up or log into your application using their existing identities. For example, to sign up or log in with a user's GitHub account, your code will look like this:
LeanCloud then verifies that the provided authData is valid and checks if a user is already associated with it. If so, it returns the status code 200 OK along with the details (including a sessionToken for the user).
If the authData is not linked to any account, you will instead receive the status code 201 Created, indicating that a new user has been created. The body of the response contains objectId, createdAt, sessionToken, and an automatically-generated unique username. For example:
{
"username": "k9mjnl7zq9mjbc7expspsxlls",
"objectId": "5b029266fb4ffe005d6c7c2e",
"createdAt": "2018-05-21T09:33:26.406Z",
"updatedAt": "2018-05-21T09:33:26.575Z",
"sessionToken": "…",
// authData won't be returned in most cases
// See explanations below
"authData": {
// …
}
// …
}
The authData field won't be returned to the client unless the current user owns it.
To ensure that each LCUser is linked to each service account only once, a unique index needs to be created for the authData.<SERVICE_NAME>.uid key in the _User class.
Authentication Data
authData is a JSON object with the names of services as keys and the details as values. You are responsible for completing the authentication flow (usually through OAuth 1.0 or 2.0) to obtain the details from the service provider which is required for linking.
A user who has GitHub linked may have the following object as authData:
LeanCloud automatically validates the access tokens for certain services to prevent data forge attack. When the validation fails, LeanCloud will respond with invalid authData error and the linking will not be established. For services that are not recognized by LeanCloud, you are responsible for validating access tokens by yourself. You can turn off the Validate access tokens when logging in with third-party accounts option in your app's Dashboard > LeanStorage > Settings if you prefer not to have LeanCloud validate access tokens for you.
Linking with Existing Users
An existing user can link their third-party accounts.
Once linked, the third-party account information will be added to the authData attribute of that user.
As your app grows in scope and user-base, you may find yourself needing more coarse-grained control over access to pieces of your data than user-linked ACLs can provide. To address this requirement, LeanCloud supports a form of role-based access control. Check the detailed ACL Guide to learn how to set it up for your objects.
In-App Searching
In-App Searching offers a better way to search through the information contained within your apps. It's built with search engine capabilities that you can easily tap into your app. Effective and useful searching functionality in your app is crucial for helping users find what they need. For more details, see In-App Searching Guide.
In-App Socializing
In-app socializing offers features like following, timeline, status update, interaction, messaging, etc. For more details, see In-App Socializing Guide.
LeanStorage Flutter Guide
The LeanStorage Flutter SDK can be used to persist and query data in LeanCloud. The code below shows how you can create an object and store it into the cloud:
The SDK designed for each language interacts with the same REST API via HTTPS, offering fully functional interfaces for you to manipulate the data in the cloud.
Installing SDK
See How to Install the Flutter SDK。
Objects
LCObject
Storing data on LeanCloud is built around
LCObject
. EachLCObject
contains key-value pairs of JSON-compatible data. This data is schema-free, which means that you don't need to specify ahead of time what keys exist on eachLCObject
. Simply set whatever key-value pairs you want, and our backend will store it.For example, the
LCObject
storing a simple todo item may contain the following data:Data Types
LCObject
supports a wide range of data types to be used for each field, including common ones likeString
,Number
,Boolean
,Object
,Array
, andDate
. You can nest objects in JSON format to store more structured data within a singleObject
orArray
field.Special data types supported by
LCObject
includePointer
andFile
, which are used to store a reference to anotherLCObject
and binary data respectively.LCObject
also supportsGeoPoint
, a special data type you can use to store location-based data. See GeoPoints for more details.Some examples:
We do not recommend storing large pieces of binary data like images or documents with
LCObject
. The size of eachLCObject
should not exceed 128 kilobytes. We recommend usingLCFile
for storing images, documents, and other types of files. To do so, createLCFile
objects and assign them to fields ofLCObject
. See Files for details.Keep in mind that our backend stores dates in UTC format and the SDK will convert them to local times upon retrieval.
The date values displayed in your app's Dashboard > LeanStorage > Data are also converted to match your operating system's time zone. The only exception is that when you retrieve these date values through our REST API, they will remain in UTC format. You can manually convert them using appropriate time zones when necessary.
To learn about how you can protect the data stored on LeanCloud, see Data and Security.
Creating Objects
The code below creates a new instance of
LCObject
with classTodo
:The constructor takes a class name as a parameter so that the cloud knows the class you are using to create the object. A class in LeanCloud is comparable to a table in a relational database. A class name starts with a letter and can only contain numbers, letters, and underscores.
Saving Objects
The following code saves a new object with class
Todo
to the cloud:To make sure the object is successfully saved, take a look at Dashboard > LeanStorage > Data >
Todo
in your app. You should see a new entry of data with something like this when you click on itsobjectId
:You don't have to create or set up a new class called
Todo
in Dashboard > LeanStorage > Data before running the code above. If the class doesn't exist, it will be automatically created.There are several built-in fields that are provided by default which you don't need to specify in your code:
objectId
String
ACL
LCACL
createdAt
DateTime
updatedAt
DateTime
Each of these fields is filled in by the cloud automatically and doesn't exist on the local
LCObject
until a save operation has been completed.Field names, or keys, can only contain letters, numbers, and underscores. A custom key can neither start with double underscores
__
, nor be identical to any system reserved words or built-in field names (ACL
,className
,createdAt
,objectId
, andupdatedAt
) regardless of letter cases.Values can be strings, numbers, booleans, or even arrays and dictionaries — anything that can be JSON-encoded. See Data Types for more information.
We recommend that you adopt CamelCase naming convention to
NameYourClassesLikeThis
andnameYourKeysLikeThis
, which keeps your code more readable.Retrieving Objects
If
LCObject
is already in the cloud, you can retrieve it using itsobjectId
with the following code:If you try to access a field or property that doesn't exist, the SDK will not raise an error. Instead, it will return
.
Updating Objects
To update an existing object, assign the new data to each field and call the
save
method. For example:LeanCloud automatically figures out which data has changed and only the fields with changes will be sent to the cloud. The fields you didn't update will remain intact.
Updating Counters
Take Twitter as an example, we need to keep track of how many Likes and Retweets a tweet has gained so far. Since a Like or Retweet action can be triggered simultaneously by multiple clients, saving objects with updated values directly can lead to inaccurate results. To make sure that the total number is stored correctly, LeanCloud allows you to atomically increase (or decrease) the value of a number field:
You can specify the amount of increment (or decrement) by providing an additional argument. If the argument is not provided,
1
is used by default.Updating Arrays
There are several operations that can be used to atomically update an array associated with a given key:
add(key, value)
appends the given object to the end of an array.
addAll(key, values)
appends the given objects to the end of an array.
addUnique(key, value)
adds the given object into an array only if it is not in it. The object will be inserted at a random position.
addAllUnique(key, values)
appends the given array objects to the end of an array ensuring that each object only appears once within the array.
remove(key, value)
removes all instances of the given object from an array.
removeAll(key, values)
removes all instances of the given objects from an array.
For example,
Todo
has a field namedalarms
for keeping track of times at which a user wants to be alerted. The following code adds the times to the alarms field:Deleting Objects
The following code deletes a
Todo
object from the cloud:You can delete a given field of an object with the
unset
method:Removing data from the cloud should always be dealt with great caution as it may lead to non-recoverable data loss. We strongly advise that you read ACL Guide to understand the risks thoroughly. You should also consider implementing class-level, object-level, and field-level permissions for your classes in the cloud to guard against unauthorized data operations.
Batch Processing
You can create, save, delete, or fetch multiple objects within a single request:
The following code sets
isComplete
of allTodo
objects to betrue
:Although each function call sends multiple operations in one single network request, saving operations and fetching operations are billed as separate API calls for each object in the collection, while deleting operations are billed as a single API call.
Data Models
Objects may have relationships with other objects. For example, in a blogging application, a
Post
object may have relationships with manyComment
objects. LeanCloud supports three kinds of relationships, including one-to-one, one-to-many, and many-to-many.One-to-One and One-to-Many Relationships
One-to-one and one-to-many relationships are modeled by saving
LCObject
as a value in the other object. For example, eachComment
in a blogging app might correspond to onePost
.The following code creates a new
Post
with a singleComment
:Internally, the backend will store the referred-to object with the
Pointer
type in just one place in order to maintain consistency. You can also link objects using theirobjectId
s like this:See Relational Queries for instructions on how to query relational data.
Many-to-Many Relationships
The easiest way to model many-to-many relationships is to use arrays. In most cases, using arrays helps you reduce the number of queries you need to make and leads to better performance. However, if additional properties need to be attached to the relationships between two classes, using join tables would be a better choice. Keep in mind that the additional properties are used to describe the relationships between classes rather than any single class.
We recommend you to use join tables if the total amount of objects of any class exceeds 100.
Modeling relationships among data could be a tough job. We have written a dedicated article to address Data Modeling in greater detail, which we highly recommend you to read.
Queries
We've already seen how you can retrieve a single object from the cloud with
LCObject
, but it doesn't seem to be powerful enough when you need to retrieve multiple objects that match certain conditions at once. In such situation,LCQuery
would be a more efficient tool you can use.Basic Queries
The general steps of performing a basic query include:
LCQuery
.The code below retrieves all
Student
objects whoselastName
isSmith
:Query Constraints
There are several ways to put constraints on the objects found by
LCObject
.The code below filters out objects with
Jack
asfirstName
:For sortable types like numbers and strings, you can use comparisons in queries:
You can apply multiple constraints to a single query, and objects will only be in the results if they match all of the constraints. In other words, it's like concatenating constraints with
AND
:You can limit the number of results by setting
limit
(defaults to100
):For performance reasons, the maximum value allowed for
limit
is1000
, meaning that LeanCloud would only return 1,000 results even it is set to be greater than1000
.If you need exactly one result, you may use
first
for convenience:You can skip certain number of results by setting
skip
:You can implement pagination in your app by using
skip
together withlimit
:Keep in mind that the higher the
skip
goes, the slower the query will run. You may consider usingcreatedAt
orupdatedAt
(which are indexed) to set range boundaries for large datasets to make queries more efficient.For sortable types, you can control the order in which results are returned:
You can even attach multiple sorting rules to a single query:
To retrieve objects that have or do not have particular fields:
You can restrict the fields returned by providing a list of keys with
. The code below retrieves todos with only the
title
andcontent
fields (and also special built-in fields such asobjectId
,createdAt
, andupdatedAt
):You can add a minus prefix to the attribute name for inverted selection. For example, if you do not care about the post author, use
-author
. The inverted selection also applies to preserved attributes, and can be used with dot notations, e.g.-pubUser.createdAt
.Queries on String Values
Use
to restrict to string values that start with a particular string. Similar to a
LIKE
operator in SQL, it is indexed so it is efficient for large datasets:Use
to restrict to string values that contain a particular string:
Unlike
whereStartsWith
,whereContains
can't take advantage of indexes, which is not encouraged to be used for large datasets.Please note that both
whereStartsWith and
whereContains
perform case-sensitive matching, so the examples above will not look for string values containingLunch
,LUNCH
, etc.If you are looking for string values that do not contain a particular string, use
whereMatches
with regular expressions:However, performing queries with regular expressions as constraints can be very expensive, especially for classes with over 100,000 records. The reason behind this is that queries like this can't take advantage of indexes and will lead to exhaustive scanning of the whole dataset to find the matching objects. We recommend that you take a look at our In-App Searching feature, a full-text search solution we provide to improve your app's searching ability and user experience.
If you are facing performance issues with queries, please refer to Optimizing Performance for possible workarounds and best practices.
Queries on Array Values
The code below looks for all the objects with
work
as an element of its array fieldtags
:To look for objects whose array field
tags
contains three elements:You can also look for objects whose array field
tags
containswork
,sales
, andappointment
:To retrieve objects whose field matches any one of the values in a given list, you can use
instead of performing multiple queries. The code below constructs a query that retrieves todo items with
priority
to be1
or2
:Conversely, you can use
whereNotContainedIn
if you want to retrieve objects that do not match any of the values in a list.Relational Queries
There are several ways to perform queries for relational data. To retrieve objects whose given field matches a particular
LCObject
, you can usejust like how you use it for other data types. For example, if each
Comment
has aPost
object in itspost
field, you can fetch all the comments for a particularPost
with the following code:To retrieve objects whose given field contains
LCObject
that matches a different query, you can use. The code below constructs a query that looks for all the comments for posts with images:
To retrieve objects whose given field does not contain
LCObject
that matches a different query, usewhereDoesNotMatchQuery
instead.Sometimes you may need to look for related objects from different classes without extra queries. In such situations, you can use
include
on the same query. The following code retrieves the last 10 comments together with the posts related to them:You can even indicate multi-level associations using dot notations. If you wanted to include the post for each comment as well as the author of the post, you can do:
query.include('post.author');
Feel free to use
as many times as you need for the same query to have multiple fields included. Related objects retrieved in this way also works with `LCQuery` helpers like
.Multi-level conditions passed into
.include
won't work with anyLCObject
contained in an array field. The furthest level that can be reached is the field itself.You can also use dot notations with
.select
to limit the fields returned from the related objects:Caveats about Inner Queries
The backend of LeanCloud is not built on relational databases, which makes it impossible to join tables while querying. For the relational queries mentioned above, what LeanCloud would do is to perform an inner query first (with
100
as defaultlimit
and1000
as maximum) and then insert the result from this query into the outer query. If the number of records matching the inner query exceeds thelimit
and the outer query contains other constraints, the amount of the records returned in the end could be zero or less than your expectation since only the records within thelimit
would be inserted into the outer query.The following actions can be taken to solve the problem:
1000
as thelimit
of the inner query.skip
values until all the records are gone through (performance issue could occur if the value ofskip
gets too big).Counting Objects
If you just need to count how many objects match a query but do not need to retrieve the actual objects, use
instead of
. For example, to count how many todos have been completed:Compound Queries
Compound queries can be used if complex query conditions need to be specified. A compound query is a logical combination (
OR
orAND
) of subqueries.Note that we do not support
GeoPoint
or non-filtering constraints (e.g.near
,withinGeoBox
,limit
,skip
,ascending
,descending
,include
) in the subqueries of a compound query.OR-ed Query Constraints
An object will be returned as long as it fulfills any one of the subqueries. The code below constructs a query that looks for all the todos that either have priorities higher than or equal to
3
, or are already completed:Queries regarding
GeoPoint
cannot be present among OR-ed queries.AND-ed Query Constraints
The effect of using AND-ed query is the same as adding constraints to
LCQuery
. The code below constructs a query that looks for all the todos that are created between2016-11-13
and2016-12-02
:While using an AND-ed query by itself doesn't bring anything new comparing to a basic query, to combine two or more OR-ed queries, you have to use AND-ed queries:
Optimizing Performance
There are several factors that could lead to potential performance issues when you conduct a query, especially when more than 100,000 records are returned at a time. We are listing some common ones here so you can design your apps accordingly to avoid them:
count
with conditions (all the entries will be gone through)skip
for a large number of entries (all the entries that need to be skipped will be gone through)Files
LCFile
allows you to store application files in the cloud that would otherwise be too large or cumbersome to fit into a regularLCObject
. The most common use case is storing images, but you can also use it for documents, videos, music, and any other binary data.Creating Files
You can also create a file from a URL:
When creating files from URLs, the SDK will not upload the actual files into the cloud but will store the addresses of the files as strings. This will not lead to actual traffic for uploading files, as opposed to creating files in other ways by doing which the files will be actually stored into the cloud.
LeanCloud will auto-detect the type of the file you are uploading based on the file extension, but you can also specify the
Content-Type
(commonly referred to as MIME type):But the most common method for creating files is to upload them from local paths:
The file we uploaded here is named
avatar.jpg
. There are a couple of things to note here:objectId
, so it is allowed for multiple files to share the same name.LCFile
, use.png
as its extension.application/octet-stream
.Saving Files
By saving a file, you store it into the cloud and get a permanent URL pointing to it:
A file successfully uploaded can be found in the
_File
class and cannot be modified later. If you need to change the file, you have to upload the modified file again and a newobjectId
and URL will be generated.You can associate a file with
LCObject
after it is saved:You can also construct a
LCQuery
to query files:Note that the
url
field of internal files (files uploaded to LeanCloud file service) is dynamically generated by the cloud, which will switch custom domain names automatically. Therefore, querying files by theurl
field is only applicable to external files (files created by saving the external URL directly to the_File
table). Query internal files by thekey
field (path in URL) instead.On a related note, if the files are referenced in an array field of
LCObject
and you want to get them within the same query forLCObject
, you need to use themethod with
LCQuery
. For example, if you are retrieving all the todos with the same titleGet Cakes
and you want to retrieve their related attachments at the same time:Upload Progress
You can monitor the progress of uploading and display that to the user:
File Metadata
When uploading a file, you can attach additional properties to it with
metaData
. A file'smetaData
cannot be updated once the file is stored to the cloud.Deleting Files
The code below deletes a file from the cloud:
By default, a file is not allowed to be deleted. You can change the setting by going to Dashboard > LeanStorage > Data >
_File
and select Others > Permission settings >delete
.CDN Support
You can set up your own CDN to improve the speed your users access the files stored on LeanCloud. Take Amazon CloudFront CDN as an example:
LCFile
and fill it into CloudFront's Origin Domain Name. Leave the other settings with defaults.GeoPoints
LeanCloud allows you to associate real-world latitude and longitude coordinates with an object by adding
LCGeoPoint
to theLCObject
. By doing so, queries on the proximity of an object to a given point can be performed, allowing you to implement functions like looking for users or places nearby easily.To associate a point with an object, you need to create the point first. The code below creates
LCGeoPoint
with39.9
aslatitude
and116.4
aslongitude
:Now you can store the point in an object as a regular field:
Geo Queries
With a number of existing objects with spatial coordinates, you can find out which of them are closest to a given point, or are contained within a particular area. This can be done by adding another restriction to
LCQuery
using. The code below returns a list of
Todo
objects withlocation
closest to a given point:Additional sorting conditions like
orderByAscending
andorderByDescending
will gain higher priorities than the default order by distance.To have the results limited within a certain distance, check out in our API docs.
You can also query for the set of objects that are contained within a rectangular bounding box with
whereWithinGeoBox
:Caveats about GeoPoints
There are a couple of things to keep in mind:
LCObject
may only have one field containingLCGeoPoint
object.-90.0
and90.0
. Longitude should be between-180.0
and180.0
. Attempting to set latitude or longitude out of bounds will cause an error.Users
At the core of many apps, there is a notion of user accounts that allows users to access their information in a secure manner. We provide a specialized user class called
LCUser
which automatically handles much of the functionality required for user account management in your app.LCUser
is a subclass ofLCObject
. Therefore, all the methods that work forLCObject
also work forLCUser
. The only difference is thatLCUser
has some additional features specific to user accounts. Each app has a dedicated_User
class for storingLCUser
.User Properties
LCUser
offers the following fields thatLCObject
does not have:username
: The username of the user.password
: The password of the user.email
: The email address of the user.emailVerified
: Whether the user has verified the email address with LeanCloud or not.mobilePhoneNumber
: The mobile phone number of the user.mobilePhoneVerified
: Whether the user has verified the mobile phone number with LeanCloud or not.We'll go through each of these in detail as we run through the various use cases for users.
Signing up
When a user first opens your app, you may want them to sign up for an account. The following code shows a typical sign-up process with username and password:
A new
LCUser
should always be created usingsignUp
rather thansave
. Subsequent updates to a user can be done with.
If the code returns the error
202
, it means that a user with the sameusername
already exists in_User
table and the client should prompt the user to try a different username. It is also required that eachemail
ormobilePhoneNumber
appears only once in the corresponding column. Otherwise, error203
or214
will occur. You may ask a user to sign up with an email address and make theusername
to be the same as theemail
. By doing so, the user can directly reset their password with email.When creating a user with username and password, the SDK sends the password to the cloud in plaintext through HTTPS and the password will be hashed once it arrives to the cloud. (The cloud has no restrictions on password length and complexity.) We never store passwords in plaintext, nor will we ever transmit passwords back to the client in plaintext. Our hashing algorithm guarantees that the original password cannot be retrieved by rainbow table attack and even app developers themselves will not be able to see the password. Keep in mind that the password should not be hashed by the client, or the password reset function will not work.
Signing up with Phones
For a mobile app, it's also common to ask users to sign up with their phone numbers instead of usernames and passwords. There are two basic steps in it. First, ask the user to enter a phone number that can receive text messages. When the user clicks on the "Get Verification Code" button, call the following method to have a 6-digit verification code sent to the phone number the user just entered:
After the verification code is entered by the user, call the following method to finish signing up:
The
username
will be the same asmobilePhoneNumber
and apassword
will be generated by LeanCloud automatically.If you wish to let the user specify their own password, you can let them fill in a password together with their mobile phone number, and then follow the process of registering with username and password described in the previous section,
submitting the user's mobile phone number as the value of both the
username
and themobilePhoneNumber
fields.If you wish, you can also check the following options in "Dashboard > LeanStorage > Users > Settings": "Do not allow users with unverified phone numbers to log in", and/or "Allow users with verified phone numbers to login with SMS".
Phone Number Format
A phone number that
LCUser
accepts should have a leading plus sign (+
) immediately followed by the country code and the phone number without any dashes, spaces, or other non-numeric characters. For instance,+8618200008888
is a valid China number (86
is the country code) and+19490008888
is a valid US or Canada number (1
is the country code).For a list of countries and regions that LeanCloud can reach out through SMS, please refer to the Pricing page on our website.
Logging in
The code below logs a user in with username and password:
Logging in with Emails
The code below logs a user in with email and password:
Logging in with Phones
If you are allowing users to sign up with their phone numbers, you can also let them log in with either a password or a verification code sent via text message. The code below logs a user in with phone number and password:
By default, LeanCloud allows a user to log in to their account as long as the phone number and the password are correct even when the ownership of the phone hasn't been verified. To make your app more secure, you can choose to allow only those who have their phones verified to log in. The option can be found in Dashboard > LeanStorage > Settings.
You may also let a user in with a verification code sent to their phone, which is useful when the user forgets the password and does not want to reset it at the moment. Similar to the steps of signing a user up with phone numbers, ask the user to enter the phone number associated with the account, and call the following method once the user clicks on the "Get Verification Code" button:
After the verification code is entered by the user, call the following method to finish logging in:
Sandbox Phone Number
During the development of your application, you may need to test the sign-up or log-in related API intensively with your phone. As there are, however, limits to how quickly messages can be sent into the carrier networks, your testing pace can be significantly affected.
To work around it, you can set up a sandbox phone number in Dashboard > Messaging > SMS > Settings. LeanCloud will issue a fixed verification code to go with that sandbox phone number. Whenever LeanCloud detects such combination of data, the user will be let right in authenticated without any connections to the carrier networks being made.
On a related note, a sandbox phone number also comes in handy for iOS apps that allow users to log in with SMS code. This is because Apple may ask developers to provide a fixed combination of phone number and verification code for them to review the app as a normal user. Failure to do so may result in their app being rejected by the App Store.
For more details regarding the limitations of sending and receiving SMS messages, see SMS Guide.
Single Device Sign-on
In some scenarios you may want to restrict a user's account to be logged on by no more than one device at a time. That is, when a user logs in to the app on a new device, all the previous sessions on other devices will become invalid. Here's the instruction about how you can implement this feature with LeanCloud:
User Account Lockout
If the wrong password or verification code is entered for an account for more than 6 times within 15 minutes, the account will be disabled temporarily and the error
{ "code": 1, "error": "You have exceeded the maximum number of login attempts, please try again later, or consider resetting your password." }
will be returned.The account will be automatically recovered 15 minutes after the last attempt and the process cannot be expedited through SDK or REST API. While the account is disabled, the user cannot be logged in even though the correct credentials are provided. The restriction applies to both client-side SDKs and LeanEngine.
Verifying Emails
You can request that your users have their email addresses verified before they can log in or access certain functions in your app. This makes it harder for spam users to abuse your app. By default, each user has an
emailVerified
field which becomesfalse
when the user first signs up or has their email address changed. In your app's Dashboard > LeanStorage > Settings, you can enable Send verification emails when users register or change email addresses from clients so that when a user signs up or changes their email address, an email containing a verification link will be sent out automatically. You can find the option to prevent users with unverified email addresses from logging in on the same page.If a user forgets to click on the link and needs to have their account verified later, the following code can be used to send a new email:
The
emailVerified
will becometrue
after the link is clicked on. This field can never betrue
when theemail
field is empty.Verifying Phone Numbers
Similar to Verifying Emails, you can also request that your users have their phone numbers verified before they can log in or access certain functions in your app. By default, each user has a
mobilePhoneVerified
field which becomesfalse
when the user first signs up or has their phone number changed. In your app's Dashboard > LeanStorage > User > Setting, you can find the option to prevent users with unverified phone numbers from logging in on the same page.You can also initiate a verification request at anytime with the following code:
After the verification code is entered by the user, call the following method and the user's
mobilePhoneVerified
will becometrue
:Verify Phone Numbers Before Updating and Binding
LeanCloud also supports verifying the number before a user binds or updates a number.
Current User
After a user is logged in, LeanCloud SDK automatically stores the session information of this user in the client so that the user does not need to log in each time they open the client. The following code checks if there is a user logged in:
The session information of a user will remain in the client until the user is logged out:
Setting The Current User
A session token will be returned to the client after a user is logged in. It will be cached by our SDK and will be used for authenticating requests made by the same
LCUser
in the future. The session token will be included in the header of each HTTP request made from the client, which helps the cloud identify theLCUser
sending the request.Below are the situations when you may need to log a user in with session token:
to get the session token of the current user).
The code below logs a user in with session token (the session token will be validated before proceeding):
For security reasons, please avoid passing session tokens as a part of URLs in non-private environments. This increases the risk that they will be captured by attackers.
If Log out the user when password is updated is checked on in Dashboard > LeanStorage > Settings, the session token of a user will be reset in the cloud after this user changes the password and the client needs to prompt the user to log in again. Otherwise,
403 (Forbidden)
will be returned as an error.The code below checks if a session token is valid:
Resetting Passwords
It's quite common for the users of an app to forget their passwords. LeanCloud provides a number of ways for them to reset their passwords.
Here is the flow of resetting password with email:
To start with, ask the user to enter the email used for the account, and call the function below:
The code above will check if there is a user in the
_User
table that has theemail
to be the same as the one provided and will send them a password reset email if so. As mentioned previously, you can make theusername
of each user to be the same as theiremail
, or collect the email separately and store it in theemail
field.The content of the password reset email is fully customizable. You can go to your app's Dashboard > Settings > Email templates and modify the corresponding template.
Alternatively, you can ask for the mobile phone number instead of the email to reset their password:
The code below sends a verification code to a number:
The code above will check if there is a user in the
_User
table that has themobilePhoneNumber
to be the same as the one provided and will send them a verification code if so.By changing the settings in Dashboard > LeanStorage > Settings, you can restrict the use of the mobile phone number for the above flow only if the
mobilePhoneVerified
field istrue
.The code below resets the password of a user after they enter the verification code and a new password:
Queries on Users
To query for users, you can simple create a new
LCQuery
for_User
:For security reasons, the
_User
table of each new app has itsfind
permission disabled by default. Each user can only access their own data in_User
table and cannot access that of others. If you need to allow each user to view other users' data, we recommend that you create a new table to store such data and enable thefind
permission of this table. You may also encapsulate queries on users within LeanEngine and avoid opening upfind
permissions of_User
tables.See Security of User Objects for other restrictions applied to the
_User
table, and Data and Security for more information regarding class-level permission settings.Associations
Associations involving
LCUser
works in the same way as basicLCObject
. The code below saves a new book for an author and retrieves all the books written by that author:Security of User Objects
The
LCUser
class is secured by default. You are not able to invoke any save- or delete-related methods unless theLCUser
was obtained using an authenticated method likeor
. This ensures that each user can only update their own data.The reason behind this is that most data stored in
LCUser
can be very personal and sensitive, such as mobile phone number, social network account ID, etc. Even the app's owner should avoid tampering with these data for the sake of user's privacy.The code below illustrates this security policy:
The
LCUser
obtained fromLCUser.getCurrent()
will always be authenticated.To check if
LCUser
is authenticated, you can invoke themethod. You do not need to check if
LCUser
is authenticated if it is obtained via an authenticated method.As a reminder, the user's password can be set when signing up but cannot be modified and saved to the cloud afterward unless the user requests it to be reset. It will not be cached on the client and will show as
null
when being retrieved from the cloud after the user is logged in.Security of Other Objects
For each given object, you can specify which users are allowed to read it and which are allowed to modify it. To support this type of security, each object has an access control list, implemented by the
class. More details can be found in ACL Guide.
Linking Users
LeanCloud allows you to link your users with services like GitHub, Twitter, and Facebook (commonly known as social networking services, or SNS), allowing your users to sign up or log into your application using their existing identities. For example, to sign up or log in with a user's GitHub account, your code will look like this:
LeanCloud then verifies that the provided
authData
is valid and checks if a user is already associated with it. If so, it returns the status code200 OK
along with the details (including asessionToken
for the user).If the
authData
is not linked to any account, you will instead receive the status code201 Created
, indicating that a new user has been created. The body of the response containsobjectId
,createdAt
,sessionToken
, and an automatically-generated uniqueusername
. For example:The
authData
field won't be returned to the client unless the current user owns it.To ensure that each
LCUser
is linked to each service account only once, a unique index needs to be created for theauthData.<SERVICE_NAME>.uid
key in the_User
class.Authentication Data
authData
is a JSON object with the names of services as keys and the details as values. You are responsible for completing the authentication flow (usually through OAuth 1.0 or 2.0) to obtain the details from the service provider which is required for linking.A user who has GitHub linked may have the following object as
authData
:LeanCloud automatically validates the access tokens for certain services to prevent data forge attack. When the validation fails, LeanCloud will respond with
invalid authData
error and the linking will not be established. For services that are not recognized by LeanCloud, you are responsible for validating access tokens by yourself. You can turn off the Validate access tokens when logging in with third-party accounts option in your app's Dashboard > LeanStorage > Settings if you prefer not to have LeanCloud validate access tokens for you.Linking with Existing Users
An existing user can link their third-party accounts. Once linked, the third-party account information will be added to the
authData
attribute of that user.For example, to link a GitHub account:
Unlinking
Similarly, a third-party account can be unlinked.
For example, the code below unlinks a user's GitHub account:
Roles
As your app grows in scope and user-base, you may find yourself needing more coarse-grained control over access to pieces of your data than user-linked ACLs can provide. To address this requirement, LeanCloud supports a form of role-based access control. Check the detailed ACL Guide to learn how to set it up for your objects.
In-App Searching
In-App Searching offers a better way to search through the information contained within your apps. It's built with search engine capabilities that you can easily tap into your app. Effective and useful searching functionality in your app is crucial for helping users find what they need. For more details, see In-App Searching Guide.
In-App Socializing
In-app socializing offers features like following, timeline, status update, interaction, messaging, etc. For more details, see In-App Socializing Guide.