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:

LCObject todo = LCObject("Todo");
todo["title"] = "R&D Weekly Meeting";
todo["content"] = "All team members, Tue 2pm";
await todo.save();

Installing SDK

See How to Install the Flutter SDK。

Objects

LCObject

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, Date, and null. 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.

Some examples:

// Basic types
int number = 2018;
bool boolValue = true;
String stringValue = 'hello, world';
DateTime now = DateTime.now();
List intList = [1, 2, 3];
Map<String, dynamic> stringMap = {
  'year': 1780,
  'first': 'partridge',
  'second': 'turtledoves',
  'fifth': 'golden rings'
};

// Create an object
LCObject object = new LCObject('Hello');
object['intValue'] = intValue;
object['boolValue'] = boolValue;
object['stringValue'] = stringValue;
object['time'] = now;
object['intList'] = intList;
object['stringMap'] = stringMap;

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.

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:

{
  "title":     "Sign up for Marathon",
  "priority":  2,
  "ACL": {
    "*": {
      "read":  true,
      "write": true
    }
  },
  "objectId":  "582570f38ac247004f39c24b",
  "createdAt": "2017-11-11T07:19:15.549Z",
  "updatedAt": "2017-11-11T07:19:15.549Z"
}

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:

DateTime alarm1 = DateTime.parse('2018-04-30 07:10:00Z');
DateTime alarm2 = DateTime.parse('2018-04-30 07:20:00Z');
DateTime alarm3 = DateTime.parse('2018-04-30 07:30:00Z');

LCObject todo = LCObject("Todo");
todo.addAllUnique('alarms', [alarm1, alarm2, alarm3]);
await todo.save();

Deleting Objects

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();

Batch Processing

You can create, save, delete, or fetch multiple objects within a single request:

LCObject.saveAll();

LCObject.deleteAll();

LCObject.fetchAll();

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.

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:

1. Creating LCQuery.
2. Putting conditions on it.
3. 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();

LCQuery<LCObject> query = LCQuery('Student');
query.whereEqualTo('lastName', 'Smith');
List<LCObject> students = await query.find();

Query Constraints

There are several ways to put constraints on the objects found by LCObject.

The code below filters out objects with Jack as firstName:

query.whereNotEqualTo('firstName', 'Jack');

For sortable types like numbers and strings, you can use comparisons in queries:

query.whereLessThan('age', 18);

query.whereLessThanOrEqualTo('age', 18);

query.whereGreaterThan('age', 18);

query.whereGreaterThanOrEqualTo('age', 18);

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:

query.whereEqualTo('firstName', 'Jack');
query.whereGreaterThan('age', 18);

You can limit the number of results by setting limit (defaults to 100):

query.limit(10);

If you need exactly one result, you may use first for convenience:

LCQuery<LCObject> query = LCQuery('Todo');
query.whereEqualTo('priority', 2);
LCObject todo = await query.first();

You can skip certain number of results by setting skip:

query.skip(20);

You can implement pagination in your app by using skip together with limit:

LCQuery<LCObject> query = LCQuery('Todo');
query.whereEqualTo('priority', 2);
query.limit(10);
query.skip(20);

For sortable types, you can control the order in which results are returned:

query.orderByAscending('createdAt');

query.orderByDescending('createdAt');

You can even attach multiple sorting rules to a single query:

query.addAscendingOrder('priority');
query.addDescendingOrder('createdAt');

To retrieve objects that have or do not have particular fields:

query.whereExists('images');

query.whereDoesNotExist('images');

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):

LCQuery<LCObject> query = LCQuery('Todo');
query.select('title');
query.select('content');
LCObject todo = await query.first();

String title = todo['title']; // √
String content = todo['content']; // √
String notes = todo['notes']; // null

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.

If you are looking for string values that do not contain a particular string, use whereMatches with regular expressions:

LCQuery query = LCQuery('Todo');
// "title" without "ticket" (case-insensitive)
query.whereMatches('title','^((?!ticket).)*\$', modifiers: 'i');

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.

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, and appointment:

query.whereContainsAll('tags', ['work', 'sales', 'appointment']);

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 1 or 2:

// Single query
LCQuery<LCObject> priorityOneOrTwo = LCQuery('Todo');
priorityOneOrTwo.whereContainedIn('priority', [1, 2]);
// Mission completed :)

// ---------------
//       vs.
// ---------------

// Multiple queries
LCQuery<LCObject> priorityOne = LCQuery('Todo');
priorityOne.whereEqualTo('priority', 1);

LCQuery<LCObject> priorityTwo = LCQuery('Todo');
priorityTwo.whereEqualTo('priority', 2);

LCQuery<LCObject> priorityOneOrTwo = LCQuery.or([priorityOne, priorityTwo]);
List<LCObject> results = await priorityOneOrTwo.find();
// Kind of verbose :(

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:

LCObject post = LCObject.createWithoutData('Post', '57328ca079bc44005c2472d0');
LCQuery<LCObject> query = LCQuery('Comment');
query.whereEqualTo('post', post);
List<LCObject> comments = await query.find();

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:

LCQuery innerQuery = LCQuery('Post');
innerQuery.whereExists('image');

LCQuery query = LCQuery('Comment');
query.whereMatchesQuery('post', innerQuery);

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.

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.

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:

LCQuery<LCObject> priorityQuery = LCQuery('Todo');
priorityQuery.whereGreaterThanOrEqualTo('priority', 3);

LCQuery<LCObject> isCompleteQuery = LCQuery('Todo');
isCompleteQuery.whereEqualTo('isComplete', true);

LCQuery<LCObject> priorityOneOrTwo = LCQuery.or([priorityQuery, isCompleteQuery]);

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:

LCQuery<LCObject> startDateQuery = new LCQuery('Todo');
startDateQuery.whereGreaterThanOrEqualTo('createdAt', DateTime.parse('2016-11-13 00:00:00Z'));

LCQuery<LCObject> endDateQuery = new LCQuery('Todo');
endDateQuery.whereLessThan('createdAt', DateTime.parse('2016-12-03 00:00:00Z'));

LCQuery<LCObject> query = LCQuery.and([startDateQuery, endDateQuery]);
List<LCObject> results = await query.find();

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:

LCQuery<LCObject> createdAtQuery = LCQuery('Todo');
createdAtQuery.whereGreaterThanOrEqualTo('createdAt', DateTime.parse('2018-04-30 00:00:00Z'));
createdAtQuery.whereLessThan('createdAt', DateTime.parse('2018-05-01 00:00:00Z'));

LCQuery<LCObject> locationQuery = LCQuery('Todo');
locationQuery.whereDoesNotExist('location');

LCQuery<LCObject> priority2Query = LCQuery('Todo');
priorityQuery.whereEqualTo('priority', 2);

LCQuery<LCObject> priority3Query = LCQuery('Todo');
priorityQuery.whereEqualTo('priority', 3);

LCQuery<LCObject> priorityQuery = LCQuery.or([priority2Query, priority3Query]);
LCQuery<LCObject> timeLocationQuery = LCQuery.or([locationQuery, createdAtQuery]);
LCQuery<LCObject> query = LCQuery.and([priorityQuery, timeLocationQuery]);

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:

• 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.

Creating Files

LCFile file = LCFile.fromBytes('resume.txt', utf8.encode('LeanCloud'));

You can also create a file from a URL:

LCFile file = LCFile.fromUrl('logo.png', 'https://leancloud.cn/assets/imgs/press/Logo%20-%20Blue%20Padding.a60eb2fa.png');

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):

LCFile file = LCFile.fromBytes('resume.txt', utf8.encode('LeanCloud'));
file.mimeType = 'application/json';

But the most common method for creating files is to upload them from local paths:

LCFile file = await LCFile.fromPath('avatar.jpg', './avatar.jpg');

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);

You can associate a file with LCObject after it is saved:

LCObject todo = LCObject('Todo');
todo['title'] = 'Get Cakes';
todo.add('attachments', file);
await todo.save();

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.

file.addMetaData('size', 1024);
file.addMetaData('width', 128);
file.addMetaData('height', 256);
file.mimeType = 'image/jpg';
await file.save();

Deleting Files

The code below deletes a file from the cloud:

LCFile file = LCObject.createWithoutData('_File', '552e0a27e4b0643b709e891e');
await file.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:

1. Read Getting Started with CloudFront.
2. Create an Amazon AWS account, and choose a CloudFront subscription plan that suits your business.
3. LeanCloud has got S3's read permission properly configured, so you can skip Step 2: Upload your content to Amazon S3 and grant object permissions in the guide and proceed with other steps.
4. 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();

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:

LCQuery<LCObject> query = LCQuery('Todo');
LCGeoPoint southwest = LCGeoPoint(30, 115);
LCGeoPoint northeast = LCGeoPoint(40, 118);
query.whereWithinGeoBox('location', southwest, northeast);

Caveats about GeoPoints

There are a couple of things to keep in mind:

• 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();

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.

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:

 await LCUser.signUpOrLoginByMobilePhone('+19490008888', '123456');

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}');
}

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:

try {
  await LCUser.signUpOrLoginByMobilePhone('+19490008888', '123456');
} on LCException catch (e) {
  print('${e.code} : ${e.message}');
}

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:

1. Create a new class that keeps track of each user's credentials and device information.
2. Each time when a user logs in on a device, update the device information of this user to be the current device.
3. 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:

await LCUser.requestEmailVerify('tom@leancloud.rocks');

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 enable Send verification SMS when users register or change phone numbers from clients so that when a user signs up or changes their phone number, a text message containing a verification code will be sent out automatically. 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:

await LCUser.requestMobilePhoneVerify('+19490008888');

After the verification code is entered by the user, call the following method and the user's mobilePhoneVerified will become true:

await LCUser.verifyMobilePhone('+19490008888','123456');

Verify Phone Numbers Before Updating and Binding

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:

await LCUser.logout();

// currentUser becomes nil
LCUser currentUser = await LCUser.getCurrent();

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 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):

await LCUser.becomeWithSessionToken('anmlwi96s381m6ca7o7266pzf');

The code below checks if a session token is valid:

LCUser currentUser = await LCUser.getCurrent();
bool isAuthenticated = await currentUser.isAuthenticated();

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:

1. The user enters the email address used for the account.
2. LeanCloud sends an email to the address including a link for resetting password.
3. After the user clicks on the link, a new page will pop up, asking for a new password.
4. The password will be reset after the user enters a new password.

To start with, ask the user to enter the email used for the account, and call the function below:

await LCUser.requestPasswordReset('tom@leancloud.rocks');

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.

Alternatively, you can ask for the mobile phone number instead of the email to reset their password:

1. The user enters the mobile phone number used for the account.
2. LeanCloud sends a short message to the number including a verification code.
3. The user types in the verification code and a new password.

The code below sends a verification code to a number:

await LCUser.requestPasswordRestBySmsCode('+19490008888');

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.

The code below resets the password of a user after they enter the verification code and a new password:

await LCUser.resetPasswordBySmsCode('+19490008888', '123456', 'cat!@#123');

Queries on Users

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:

LCObject todo = LCObject('Book');
LCUser author = await LCUser.getCurrent();
todo['title'] = 'My Fifth Book';
todo['author'] = author;
await todo.save();

LCQuery<LCObject> query = LCQuery('Book');
query.whereEqualTo('author', author);
List<LCObject> books = await query.find();

Security of User Objects

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:

var thirdPartyData = {
  // Required
  'uid':        'UID',
  'access_token':  'ACCESS_TOKEN',
  'expires_in':    7200,

  // Optional
  'refresh_token': 'REFRESH_TOKEN',
  'scope':         'SCOPE'
};
LCUser currentUser = await LCUser.loginWithAuthData(thirdPartyData, 'github');

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:

{
  "github": {
    "uid":           "…",
    "access_token":  "…",
    "expires_in":    7200,
    "refresh_token": "…",
    "scope":         "…"
  }
}

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.

Unlinking

You can unlink a service by setting the authData for the service to null. The code below unlinks a user's GitHub account:

LCUser currentUser = await LCUser.getCurrent();
await currentUser.disassociateWithAuthData('github');

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.