LeanStorage JavaScript Guide

The LeanStorage JavaScript 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:

// Declare a class
const Todo = AV.Object.extend('Todo');

// Create an object
const todo = new Todo();

// Set values of fields
todo.set('title',   'R&D Weekly Meeting');
todo.set('content', 'All team members, Tue 2pm');

// Save the object to the cloud
todo.save().then((todo) => {
  // Execute any logic that should take place after the object is saved
  console.log(`Object saved. objectId: ${todo.id}`);
}, (error) => {
  // Execute any logic that should take place if the save fails
});

Installing SDK

See How to Install the JavaScript SDK.

Web Security

If you are using our JavaScript SDK in your browser-based application, you must configure whitelist domains in your app's Dashboard > Settings > Security before you deploy it to a production environment. Once set up, our backend will only accept requests sent from domains in the whitelist, which prevents unauthorized usage or access to your cloud data on a certain level.

However, since your app is exposed to the Internet, merely setting up whitelist domains can't guarantee the security of your app. LeanCloud offers a variety of ways to help you secure your apps as well as the data stored within them. The following articles give you the necessary information you need to know regarding app security.

• Data and Security
• ACL Guide

Objects

AV.Object

Storing data on LeanCloud is built around AV.Object. Each AV.Object 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 AV.Object. Simply set whatever key-value pairs you want, and our backend will store it.

For example, the AV.Object 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

AV.Object 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 AV.Object include Pointer and File, which are used to store a reference to another AV.Object and binary data respectively.

AV.Object also supports GeoPoint, a special data type you can use to store location-based data. See GeoPoints for more details.

Some examples:

// Basic types
const bool   = true;
const number = 2018;
const string = `${number} Top Hit Songs`;
const date   = new Date();
const array  = [string, number];
const object = {
  number: number,
  string: string
};

// Create an object
const TestObject = AV.Object.extend('TestObject');
const testObject = new TestObject();
testObject.set('testNumber',  number);
testObject.set('testString',  string);
testObject.set('testDate',    date);
testObject.set('testArray',   array);
testObject.set('testObject',  object);
testObject.save();

We do not recommend storing large pieces of binary data like images or documents with AV.Object. The size of each AV.Object should not exceed 128 kilobytes. We recommend using AV.File for storing images, documents, and other types of files. To do so, create AV.File objects and assign them to fields of AV.Object. 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 AV.Object with class Todo:

// Create a new subclass of AV.Object
const Todo = AV.Object.extend('Todo');

// Create a new instance of that class
const todo = new Todo();

// You can also use the AV.Object constructor directly
const todo = new AV.Object('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.

If you're using ES6 in your codebase, you can subclass AV.Object with the extends keyword. However, when using extends, the SDK is not automatically aware of your subclasses. You will need to register the subclasses with the SDK:

class Todo extends AV.Object {
  // More properties and methods
}

// Register the subclass
AV.Object.register(Todo);

After doing this, you will be able to add additional methods and properties to your subclasses of AV.Object.

Saving Objects

The following code saves a new object with class Todo to the cloud:

// Declare a class
const Todo = AV.Object.extend('Todo');

// Create an object
const todo = new Todo();

// Set values of fields
todo.set('title', 'Sign up for Marathon');
todo.set('priority', 2);

// Save the object to the cloud
todo.save().then((todo) => {
  // Execute any logic that should take place after the object is saved
  console.log(`Object saved. objectId: ${todo.id}`);
}, (error) => {
  // Execute any logic that should take place if the save fails
});

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	AV.ACL	Access Control List, a special object defining the read and write permissions of other people.
createdAt	Date	The time the object was created.
updatedAt	Date	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 AV.Object 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 AV.Object is already in the cloud, you can retrieve it using its objectId with the following code:

const query = new AV.Query('Todo');
query.get('582570f38ac247004f39c24b').then((todo) => {
  // todo is the instance of the Todo object with objectId 582570f38ac247004f39c24b
  const title     = todo.get('title');
  const priority  = todo.get('priority');

  // Acquire special properties
  const objectId  = todo.id;
  const updatedAt = todo.updatedAt;
  const createdAt = todo.createdAt;
});

After retrieving an object, you can use the get method to acquire the data stored in its fields. Be aware that objectId, updatedAt, and createdAt are 3 special properties that cannot be retrieved using the get method or modified with the set method. Each of these fields is filled in by the cloud only, so they don't exist on AV.Object until a save operation has been completed.

If you try to access a field or property that doesn't exist, the SDK will not raise an error. Instead, it will return undefined.

Sometimes you may want to get all the fields back at one time without calling get on each field of the object. This could be helpful when you implement data binding. To do so, call toJSON on AV.Object:

const query = new AV.Query('Todo');
query.get('582570f38ac247004f39c24b').then((todo) => {
  console.log(todo.toJSON());
  // {
  //   createdAt: "2017-03-08T11:25:07.804Z",
  //   objectId: "582570f38ac247004f39c24b",
  //   priority: 2,
  //   title: "R&D Weekly Meeting",
  //   updatedAt: "2017-03-08T11:25:07.804Z"
  // }
});

Refreshing Objects

If you need to refresh a local object with the latest version of it in the cloud, call the fetch method on it:

const todo = AV.Object.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo.fetch().then((todo) => {
  // todo is refreshed
});

Keep in mind that any unsaved changes made to the object prior to calling fetch will be discarded. To avoid this, you have the option to provide a list of keys when calling the method so that only the fields being specified are retrieved and refreshed (including special built-in fields such as objectId, createdAt, and updatedAt). Changes made to other fields will remain intact.

const todo = AV.Object.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo.fetch({
  keys: 'priority, location'
}).then((todo) => {
  // 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:

const todo = AV.Object.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo.set('content', 'Weekly meeting has been rescheduled to Wed 3pm for this week.');
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.

To view which attributes have unsaved changes, you can invoke the dirtyKeys method:

todo.dirtyKeys() // ['content']

To revert unsaved changes, you can invoke the revert method. Invoking revert() without passing any parameter will revoke all unsaved changes. To specify attributes to be revoked, pass an array as parameter:

todo.revert(['content'])

Updating Data Conditionally

By passing in a query option when saving, you can specify conditions on the save operation so that the object can be updated atomically only when those conditions are met. If no object matches the conditions, the cloud will return error 305 to indicate that there was no update taking place.

For example, in the class Account there is a field called balance, and there are multiple incoming requests that want to modify this field. Since an account cannot have a negative balance, we can only allow a request to update the balance when the amount requested is lower than or equal to the balance:

const account = AV.Object.createWithoutData('Account', '5745557f71cfe40068c6abe0');
// Atomically decrease balance by 100
const amount = -100;
account.increment('balance', amount);
account.save(null, {
  // Add the condition
  query: new AV.Query('Account').greaterThanOrEqualTo('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.
  fetchWhenSave: true
}).then((account) => {
  console.log(`Balance: ${account.get('balance')}`);
}, (error) => {
  if (error.code === 305) {
    console.error('Insufficient balance. Operation failed!');
  }
});

query option only works for existing objects. In other words, it has no effect on objects that haven't been saved to the cloud yet.

The benefit of using query option instead of combining AV.Query and AV.Object shows up when you have multiple clients trying to update the same field at the same time. The latter way is more cumbersome and may lead to potential inconsistencies.

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:

• AV.Object.add('arrayKey', value)
  appends the given object to the end of an array.
• AV.Object.addUnique('arrayKey', value)
  adds the given object into an array only if it is not in it. The object will be inserted at a random position.
• AV.Object.remove('arrayKey', value)
  removes all instances of the given object 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:

const alarm1 = new Date('2018-04-30T07:10:00');
const alarm2 = new Date('2018-04-30T07:20:00');
const alarm3 = new Date('2018-04-30T07:30:00');

const alarms = [alarm1, alarm2, alarm3];

const todo = new AV.Object('Todo');
todo.addUnique('alarms', alarms);
todo.save();

Deleting Objects

The following code deletes a Todo object from the cloud:

const todo = AV.Object.createWithoutData('Todo', '582570f38ac247004f39c24b');
todo.destroy();

You can delete a given field of an object with the unset method:

const todo = AV.Object.createWithoutData('Todo', '582570f38ac247004f39c24b');

// The priority field will be removed
todo.unset('priority');

// Save the object to the cloud
todo.save();

Batch Processing

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

// Create an array for storing AV.Objects
const objects = [];

// Batch create and update
AV.Object.saveAll(objects);

// Batch delete
AV.Object.destroyAll(objects);

// Batch fetch
AV.Object.fetchAll(objects);

The following code sets isComplete of all Todo objects to be true:

const query = new AV.Query('Todo');
query.find().then((todos) => {
  // Get a collection of todos to work on
  todos.forEach((todo) => {
    // Update value
    todo.set('isComplete', true);
  });
  // Save all at once
  AV.Object.saveAll(todos);
});

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 AV.Object 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
const post = new AV.Object('Post');
post.set('title', 'I am starving!');
post.set('content', 'Hmmm, where should I go for lunch?');

// Create a comment
const comment = new AV.Object('Comment');
comment.set('content', 'KFC is the best!');

// Add the post as a property of the comment
comment.set('parent', post);

// This will save both post and comment
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:

const post = AV.Object.createWithoutData('Post', '57328ca079bc44005c2472d0');
comment.set('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 AV.Object, 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, AV.Query would be a more efficient tool you can use.

Basic Queries

The general steps of performing a basic query include:

1. Creating AV.Query.
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:

const query = new AV.Query('Student');
query.equalTo('lastName', 'Smith');
query.find().then((students) => {
  // students is an array of Student objects satisfying conditions
});

Query Constraints

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

The code below filters out objects with Jack as firstName:

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

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

// Restricts to age < 18
query.lessThan('age', 18);

// Restricts to age <= 18
query.lessThanOrEqualTo('age', 18);

// Restricts to age > 18
query.greaterThan('age', 18);

// Restricts to age >= 18
query.greaterThanOrEqualTo('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.equalTo('firstName', 'Jack');
query.greaterThan('age', 18);

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

// Limit to at most 10 results
query.limit(10);

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

const query = new AV.Query('Todo');
query.equalTo('priority', 2);
query.first().then((todo) => {
  // todo is the first Todo object satisfying conditions
});

You can skip certain number of results by setting skip:

// Skip the first 20 results
query.skip(20);

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

const query = new AV.Query('Todo');
query.equalTo('priority', 2);
query.limit(10);
query.skip(20);

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

// Sorts the results in ascending order by the createdAt property
query.ascending('createdAt');

// Sorts the results in descending order by the createdAt property
query.descending('createdAt');

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

query.addAscending('priority');
query.addDescending('createdAt');

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

// Finds objects that have the 'images' field
query.exists('images');

// Finds objects that don't have the 'images' field
query.doesNotExist('images');

You can use the matchesKeyInQuery method to look for objects with values of fields matching those of objects returned by another query.

For example, if you have a Country class matching countries with languages and a Student class matching students with their nationalities:

name	language
US	English
UK	English
China	Chinese

fullName	nationality
John Doe	US
Tom Sawyer	UK
Ming Li	China

The following code looks for all the students who are from English-speaking countries:

const studentQuery = new AV.Query('Student');
const countryQuery = new AV.Query('Country');
// Get all English-speaking countries
countryQuery.equalTo('language', 'English');
// Match Student's nationality with Country's name
studentQuery.matchesKeyInQuery('nationality', 'name', countryQuery);
studentQuery.find().then((students) => {
  // students contains John Doe and Tom Sawyer
});

You can restrict the fields returned by providing a list of keys with select. The code below retrieves todos with only the title and content fields (and also special built-in fields such as objectId, createdAt, and updatedAt):

const query = new AV.Query('Todo');
query.select(['title', 'content']);
query.first().then((todo) => {
  const title = todo.get('title'); // √
  const content = todo.get('content'); // √
  const notes = todo.get('notes'); // undefined
});

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.

The unselected fields can be fetched later with fetch. See Refreshing Objects.

Queries on String Values

Use startsWith 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:

const query = new AV.Query('Todo');
// SQL equivalent: title LIKE 'lunch%'
query.startsWith('title', 'lunch');

Use contains to restrict to string values that contain a particular string:

const query = new AV.Query('Todo');
// SQL equivalent: title LIKE '%lunch%'
query.contains('title', 'lunch');

Unlike startsWith, contains 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 matches with regular expressions:

const query = new AV.Query('Todo');
// 'title' without 'ticket' (case-insensitive)
const regExp = new RegExp('^((?!ticket).)*$', 'i');
query.matches('title', regExp);

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.equalTo('tags', 'work');

To look for objects whose array field tags contains three elements:

query.sizeEqualTo('tags', 3);

You can also look for objects whose array field tags contains work, sales, and appointment:

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

To retrieve objects whose field matches any one of the values in a given list, you can use containedIn instead of performing multiple queries. The code below constructs a query that retrieves todo items with priority to be 1 or 2:

// Single query
const priorityOneOrTwo = new AV.Query('Todo');
priorityOneOrTwo.containedIn('priority', [1, 2]);
// Mission completed :)

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

// Multiple queries
const priorityOne = new AV.Query('Todo');
priorityOne.equalTo('priority', 1);

const priorityTwo = new AV.Query('Todo');
priorityTwo.equalTo('priority', 2);

const priorityOneOrTwo = AV.Query.or(priorityOne, priorityTwo);
// Kind of verbose :(

Conversely, you can use notContainedIn 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 AV.Object, you can use equalTo 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:

const post = AV.Object.createWithoutData('Post', '57328ca079bc44005c2472d0');
const query = new AV.Query('Comment');
query.equalTo('post', post);
query.find().then((comments) => {
  // comments contains the comments for the post
});

To retrieve objects whose given field contains AV.Object that matches a different query, you can use matchesQuery. The code below constructs a query that looks for all the comments for posts with images:

const innerQuery = new AV.Query('Post');
innerQuery.exists('image');

const query = new AV.Query('Comment');
query.matchesQuery('post', innerQuery);

To retrieve objects whose given field does not contain AV.Object that matches a different query, use doesNotMatchQuery 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:

const query = new AV.Query('Comment');

// Retrieve the most recent ones
query.descending('createdAt');

// Only retrieve the last 10
query.limit(10);

// Include the related post together with each comment
query.include('post');

query.find().then((comments) => {
  // comments contains the last 10 comments including the post associated with each
  comments.forEach((comment) => {
    // This does not require a network access
    const post = comment.get('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 include as many times as you need for the same query to have multiple fields included. Related objects retrieved in this way also works with AV.Query helpers like first and get.

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 count instead of find. For example, to count how many todos have been completed:

const query = new AV.Query('Todo');
query.equalTo('isComplete', true);
query.count().then((count) => {
  console.log(`${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:

const priorityQuery = new AV.Query('Todo');
priorityQuery.greaterThanOrEqualTo('priority', 3);

const isCompleteQuery = new AV.Query('Todo');
isCompleteQuery.equalTo('isComplete', true);

const query = AV.Query.or(priorityQuery, isCompleteQuery);

AND-ed Query Constraints

The effect of using AND-ed query is the same as adding constraints to AV.Query. The code below constructs a query that looks for all the todos that are created between 2016-11-13 and 2016-12-02:

const startDateQuery = new AV.Query('Todo');
startDateQuery.greaterThanOrEqualTo('createdAt', new Date('2016-11-13 00:00:00'));

const endDateQuery = new AV.Query('Todo');
endDateQuery.lessThan('createdAt', new Date('2016-12-03 00:00:00'));

const query = AV.Query.and(startDateQuery, endDateQuery);

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:

const createdAtQuery = new AV.Query('Todo');
createdAtQuery.greaterThanOrEqualTo('createdAt', new Date('2018-04-30'));
createdAtQuery.lessThan('createdAt', new Date('2018-05-01'));

const locationQuery = new AV.Query('Todo');
locationQuery.doesNotExist('location');

var priority2Query = new AV.Query('Todo');
priority2Query.equalTo('priority', 2);

var priority3Query = new AV.Query('Todo');
priority3Query.equalTo('priority', 3);

var priorityQuery = AV.Query.or(priority2Query, priority3Query);
var timeLocationQuery = AV.Query.or(locationQuery, createdAtQuery);
var query = AV.Query.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)

LiveQuery

LiveQuery is, as its name implies, derived from AV.Query but has enhanced capability. It allows you to automatically synchronize data changes from one client to other clients without writing complex code, making it suitable for apps that need real-time data.

Suppose you are building an app that allows multiple users to edit the same file at the same time. AV.Query would not be an ideal tool since it is based on a pull model and you cannot know when to query from the cloud to get the updates.

To solve this problem, we introduced LiveQuery. This tool allows you to subscribe to the AV.Querys you are interested in. Once subscribed, the cloud will notify clients by generating event messages whenever AV.Objects that match the AV.Query are created or updated, in real-time.

Behind the scene, we use WebSocket connections to have clients and the cloud communicate with each other and maintain the subscription status of clients. In most cases, it isn't necessary to deal with the WebSocket connections directly, so we developed a simple API to help you focus on your business logic rather than technical implementations.

Initializing LiveQuery

To use LiveQuery in your app, go to your app's Dashboard > LeanStorage > Settings and check the Enable LiveQuery option under the Other section, then include the following npm module in your project:

// No need to require leancloud-storage if the following line is present
const AV = require('leancloud-storage/live-query');

Or load it with the following <script> tag:

<!-- No need to load av-min.js if the following script is present -->
<script src="//cdn.jsdelivr.net/npm/leancloud-storage@4.12.0/dist/av-live-query-min.js"></script>

See Installing SDK for more details.

Demo

We’ve made a demo app called “LeanTodo” which shows the functionality of LiveQuery. If you’d like to try it:

1. Go to https://leancloud.github.io/leantodo-vue/, enter a username and a password, and then hit “Signup”.
2. Open the same URL on a different device, enter the same credentials, and hit “Login”.
3. Create, edit, or delete some items on one device and watch what happens on the other one.

Creating a Subscription

To make a query live, create a normal AV.Query object, put conditions on it if there are, and then subscribe to it:

const query = new AV.Query('Todo');
query.subscribe().then((liveQuery) => {
  // Query becomes live after getting a subscription
});

Now you will be able to receive updates related to AV.Object. If an Todo object is created by another client with Update Portfolio as title, the following code can get the new Todo for you:

const query = new AV.Query('Todo');
query.subscribe().then((liveQuery) => {
  liveQuery.on('create', (newTodo) => {
    console.log(newTodo.get('title')); // Update Portfolio
  });
});

If someone updates this Todo by changing its content to Add my recent paintings, the following code can get the updated version for you:

liveQuery.on('update', (updatedTodo, updatedKeys) => {
  console.log(updatedTodo.get('content')); // Add my recent paintings
});

Event Handling

The following types of data changes can be monitored once a subscription is set up:

• create
• update
• enter
• leave
• delete

create Event

A create event will be triggered when a new AV.Object is created and it fulfills the AV.Query you subscribed. The object is the new AV.Object being created:

liveQuery.on('create', (object) => {
  console.log('Object created.');
});

update Event

An update event will be triggered when an existing AV.Object fulfilling the AV.Query you subscribed is updated. The object is the AV.Object being updated:

liveQuery.on('update', (object, updatedKeys) => {
  console.log('Object updated.');
});

enter Event

An enter event will be triggered when an existing AV.Object's old value does not fulfill the AV.Query you subscribed but its new value does. The object is the AV.Object entering the AV.Query and its content is the latest value of it:

liveQuery.on('enter', (object, updatedKeys) => {
  console.log('Object entered.');
});

leave Event

A leave event will be triggered when an existing AV.Object's old value fulfills the AV.Query you subscribed but its new value does not. The object is the AV.Object leaving the AV.Query and its content is the latest value of it:

liveQuery.on('leave', (object, updatedKeys) => {
  console.log('Object left.');
});

delete Event

A delete event will be triggered when an existing AV.Object fulfilling the AV.Query you subscribed is deleted. The object is the objectId of the AV.Object being deleted:

liveQuery.on('delete', (object) => {
  console.log('Object deleted.');
});

Unsubscribing

You can cancel a subscription to stop receiving events regarding AV.Query. After that, you won't get any events from the subscription.

liveQuery.unsubscribe().then(() => {
  // Successfully unsubscribed
});

Losing Connections

There are different scenarios regarding losing connections:

1. The connection to the Internet is lost unexpectedly.
2. The user performs certain operations outside of the app, like switching the app to the background, turning off the phone, or turning on the flight mode.

For the scenarios above, you don't need to do any extra work. As long as the user switches back to the app, the SDK will automatically re-establish the connection.

There is another scenario when the user completely kills the app or closes the web page. In this case, the SDK cannot automatically re-establish the connection. You will have to create subscriptions again by yourself.

Caveats about LiveQuery

Given the real-time feature of LiveQuery, developers may find it tempting to use it for instant messaging. As LiveQuery is neither designed nor optimized for completing such tasks, we discourage such use of this tool, let alone there will be an additional cost for saving message history and rising challenges of code maintenance. We recommend using our real-time messaging solution for this scenario.

Files

AV.File allows you to store application files in the cloud that would otherwise be too large or cumbersome to fit into a regular AV.Object. 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 create a file from a base64-encoded string:

const data = { base64: 'TGVhbkNsb3Vk' };
// resume.txt is the file name
const file = new AV.File('resume.txt', data);

You can also create a file from an array of byte values:

const data = [0x4c, 0x65, 0x61, 0x6e, 0x43, 0x6c, 0x6f, 0x75, 0x64];
const file = new AV.File('resume.txt', data);

What's more, you can also create a file from a Blob (in Browser), and Buffer or Stream (in Node.js).

For React Native applications, you can create a file from a local path:

const data = { blob: { uri: localFileUri } }
const file = new AV.File('resume.txt', data)

You can also create a file from a URL:

const file = AV.File.withURL(
  '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):

const file = new AV.File('resume.txt', data, 'application/json');

But the most common method for creating files is to upload them from local paths. In a web app, you can first create an input button in the user interface:

<input type="file" id="avatar-upload" />

Then get a reference to that file in a click handler:

const avatarUpload = document.getElementById('avatar-upload');
if (avatarUpload.files.length) {
  const localFile = avatarUpload.files[0];
  const file = new AV.File('avatar.jpg', localFile);
}

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 AV.File, 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.

You can specify the path of the uploaded file via the key property. For example, use a robots.txt to restrict search engines from crawling uploaded files:

file.save({ key: 'robots.txt' });

Saving Files

By saving a file, you store it into the cloud and get a permanent URL pointing to it:

file.save().then((file) => {
  console.log(`File uploaded. objectId: ${file.id}`);
}, (error) => {
  // The file either could not be read or could not be saved to LeanCloud
});

To preserve original file name in the resulting url, pass the keepFileName parameter to the save method:

const data = [0x4c, 0x65, 0x61, 0x6e, 0x43, 0x6c, 0x6f, 0x75, 0x64];
const file = new AV.File('resume.txt', data);
file.save({ keepFileName: true }).then((file) => {
  console.log(file.url); // https://your-file-domain/5112b94e0536e995741c/resume.txt
}, (error) => {
  console.error(error);
});

You can associate a file with AV.Object after it is saved:

const Todo = AV.Object.extend('Todo');
const todo = new Todo();
todo.set('title', 'Get Cakes');
// attachments is an Array field
todo.add('attachments', file);
todo.save();

You can also construct a AV.Query to query files:

const query = new AV.Query('_File');

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 AV.Object and you want to get them within the same query for AV.Object, you need to use the include method with AV.Query. 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
const query = new AV.Query('Todo');
query.equalTo('title', 'Get Cakes');
query.exists('attachments');

// Include attachments with each todo
query.include('attachments');

query.find().then((todos) => {
  todos.forEach((todo) => {
    // Get attachments array for each todo
    const attachments = todo.get('attachments');
    attachments.forEach((attachment) => {
      // Each attachment is an AV.File instance
      console.log(`URL of the attachment: ${attachment.get('url')}`);
    });
  });
});

Upload Progress

You can monitor the progress of uploading and display that to the user:

file.save({
  onprogress: (progress) => {
    console.log(progress);
    // {
    //   loaded:  1024,
    //   total:   2048,
    //   percent: 50
    // }
  }
}).then((file) => {
  // Things to do after saving
});

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.

// Set metadata
file.metaData('author', 'LeanCloud');
file.save().then((file) => {
  // Get all metadata
  const metadata = file.metaData();
  // Get author
  const author = file.metaData('author');
  // Get file name
  const fileName = file.get('name');
  // Get size (not available for files created from base64-encoded strings or URLs)
  const size = file.size();
});

Deleting Files

The code below deletes a file from the cloud:

const file = AV.File.createWithoutData('552e0a27e4b0643b709e891e');
file.destroy();

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 AV.File and fill it into CloudFront's Origin Domain Name. Leave the other settings with defaults.

Promises

Each asynchronous method in LeanCloud JavaScript SDK returns a Promise which can be used to handle the completion and exception of the method. The example below updates an AV.Object after it is being queried:

const query = new AV.Query('Todo');
query.equalTo('priority', 1);
// find is asynchronous which gives back a Promise that then can be called on
query.find().then((todos) => {
  // Returns a list of objects
  const todo = todos[0];
  todo.set('notes', 'Needs to be finished today.');
  // save is also asynchronous which gives back a Promise that you can return here and chain another Promise afterwards
  return todo.save();
}).then(() => {
  // The Promise returned by save method
  console.log('Successfully updated todo.');
}).catch((error) => {
  // Put catch at the very end of Promise chain which catches all the errors
  console.error(error);
});

The then Method

Each Promise has a method called then which takes in two callbacks. The first callback is called when the Promise is resolved (runs successfully) while the second one is called when it is rejected (gets error):

todo.save().then((todo) => {
  console.log('Successfully updated todo.');
}, (error) => {
  console.error(error);
});

The second callback is optional.

You may also implement your logic with catch:

todo.save().then((todo) => {
  console.log('Successfully updated todo.');
}).catch((error) => {
  console.error(error);
});

Chaining Promises Together

Promise allows you to connect asynchronous requests elegantly according to the order they should be called. If the callback of a Promise returns another Promise, the callback in the second then will not be resolved unless the one in the first then is resolved. This is also called Promise Chain.

// Add contents to the page following the order of chapters
const chapterIds = [
  '584e1c408e450a006c676162', // Chapter One
  '584e1c43128fe10058b01cf5', // Chapter Two
  '581aff915bbb500059ca8d0b'  // Chapter Three
];

new AV.Query('Chapter').get(chapterIds[0]).then((chapterOne) => {
  // Add contents to the page
  addHtmlToPage(chapterOne.get('content'));
  // Return the new Promise
  return new AV.Query('Chapter').get(chapterIds[1]);
}).then((chapterTwo) => {
  addHtmlToPage(chapterTwo.get('content'));
  return new AV.Query('Chapter').get(chapterIds[2]);
}).then((chapterThree) => {
  addHtmlToPage(chapterThree.get('content'));
  // Done
});

Error Handling with Promises

If any single Promise in the chain throws an error, all the callbacks following it meant for successful operations will be skipped until an error handling callback is encountered.

It is a common practice to attach an error handling function at the end of a Promise chain.

The code above can be rewritten with catch in the following way:

new AV.Query('Chapter').get(chapterIds[0]).then((chapterOne) => {
  addHtmlToPage(chapterOne.get('content'));
  // Force an error
  throw new Error('Error');
  return new AV.Query('Chapter').get(chapterIds[1]);
}).then((chapterTwo) => {
  // The code here will be ignored
  addHtmlToPage(chapterTwo.get('content'));
  return new AV.Query('Chapter').get(chapterIds[2]);
}).then((chapterThree) => {
  // The code here will be ignored
  addHtmlToPage(chapterThree.get('content'));
}).catch((error) => {
  // This error handling function will be called, printing out the error message 'Error'
  console.error(error.message);
});

async and await

async and await allows you to use Promise by writing code in a more synchronous manner:

async function example() {
  try {
    const query = new AV.Query('Todo');
    query.equalTo('priority', 1);
    const todos = await query.find();
    const todo = todos[0];
    todo.set('notes', 'Needs to be finished today.');
    return await todo.save();
  } catch (error) {
    console.error(error);
  }
}

Further reading on Promises:

• Promises/A+ Proposal

GeoPoints

LeanCloud allows you to associate real-world latitude and longitude coordinates with an object by adding AV.GeoPoint to the AV.Object. 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 AV.GeoPoint with 39.9 as latitude and 116.4 as longitude:

const point = new AV.GeoPoint(39.9, 116.4);

// Other ways of creating the same AV.GeoPoint
const point = new AV.GeoPoint([39.9, 116.4]);
const point = new AV.GeoPoint({ latitude: 39.9, longitude: 116.4 });

Now you can store the point in an object as a regular field:

todo.set('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 AV.Query using near. The code below returns a list of Todo objects with location closest to a given point:

const query = new AV.Query('Todo');
const point = new AV.GeoPoint(39.9, 116.4);
query.near('location', point);

// Limit to 10 results
query.limit(10);
query.find().then((todos) => {
  // todos is an array of Todo objects satisfying conditions
});

To have the results limited within a certain distance, check out withinKilometers, withinMiles, and withinRadians in our API docs.

You can also query for the set of objects that are contained within a rectangular bounding box with withinGeoBox:

const query = new AV.Query('Todo');
const southwest = new AV.GeoPoint(30, 115);
const northeast = new AV.GeoPoint(40, 118);
query.withinGeoBox('location', southwest, northeast);

Caveats about GeoPoints

There are a couple of things to keep in mind:

• Each AV.Object may only have one field containing AV.GeoPoint 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 AV.User which automatically handles much of the functionality required for user account management in your app.

AV.User is a subclass of AV.Object. Therefore, all the methods that work for AV.Object also work for AV.User. The only difference is that AV.User has some additional features specific to user accounts. Each app has a dedicated _User class for storing AV.User.

User Properties

AV.User offers the following fields that AV.Object 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
const user = new AV.User();

// Same as user.set('username', 'Tom')
user.setUsername('Tom');
user.setPassword('cat!@#123');

// Optional
user.setEmail('tom@leancloud.rocks');
user.setMobilePhoneNumber('+19490008888');

// Other fields can be set in the same way as AV.Object
user.set('gender', 'secret');

user.signUp().then((user) => {
  // Sign-up completed
  console.log(`User created. objectId: ${user.id}`);
}, (error) => {
  // Sign-up failed (often because the username is already taken)
});

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:

AV.Cloud.requestSmsCode('+19490008888');

After the verification code is entered by the user, call the following method to finish signing up:

AV.User.signUpOrlogInWithMobilePhone('+19490008888', '123456').then((user) => {
  // Sign-up completed
  console.log(`User created. objectId: ${user.id}`);
}, (error) => {
  // Verification code is incorrect
});

Phone Number Format

A phone number that AV.User 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:

AV.User.logIn('Tom', 'cat!@#123').then((user) => {
  // Logged in successfully
}, (error) => {
  // Failed to log in (the password may be incorrect)
});

Logging in with Emails

The code below logs a user in with email and password:

AV.User.loginWithEmail('tom@leancloud.rocks', 'cat!@#123').then((user) => {
  // Logged in successfully
}, (error) => {
  // Failed to log in (the password may be incorrect)
});

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:

AV.User.logInWithMobilePhone('+19490008888', 'cat!@#123').then((user) => {
  // Logged in successfully
}, (error) => {
  // Failed to log in (the password may be incorrect)
});

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:

AV.User.requestLoginSmsCode('+19490008888');

After the verification code is entered by the user, call the following method to finish logging in:

AV.User.logInWithMobilePhoneSmsCode('+19490008888', '123456').then((user) => {
  // Logged in successfully
}, (error) => {
  // Verification code is incorrect
});

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:

AV.User.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 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:

AV.User.requestMobilePhoneVerify('+19490008888');

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

AV.User.verifyMobilePhone('123456').then(() => {
  // mobilePhoneVerified is set to true
}, (error) => {
  // Verification code is incorrect
});

Verify Phone Numbers Before Updating and Binding

LeanCloud also supports verifying the number before a user binds or updates a number.

AV.User.requestChangePhoneNumber('+19490008888');

AV.User.changePhoneNumber('+19490008888', '123456').then(() => {
    // update local data
    const currentUser = AV.User.current();
    currentUser.setMobilePhoneNumber('+19490008888');
}, (error) => {
    // verification code is invalid
});

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:

const currentUser = AV.User.current();
if (currentUser) {
  // 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:

AV.User.logOut();

// currentUser becomes null
const currentUser = AV.User.current();

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 AV.User 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 AV.User 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 AV.User.current().getSessionToken() 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):

AV.User.become('anmlwi96s381m6ca7o7266pzf').then((user) => {
  // Logged in successfully
}, (error) => {
  // Session token is invalid
});

The code below checks if a session token is valid:

const currentUser = AV.User.current();
currentUser.isAuthenticated().then((authenticated) => {
  if (authenticated) {
    // The session token is valid
  } else {
    // The session token is invalid
  }
});

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:

AV.User.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:

AV.User.requestPasswordResetBySmsCode('+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:

AV.User.resetPasswordBySmsCode('123456', 'cat!@#123').then(() => {
  // Password is updated
}, (error) => {
  // Verification code is incorrect
});

Queries on Users

To query for users, you can simple create a new AV.Query for _User:

const userQuery = new AV.Query('_User');

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 AV.User works in the same way as basic AV.Object. The code below saves a new book for an author and retrieves all the books written by that author:

const Book = AV.Object.extend('Book');
const book = new Book();
const author = AV.User.current();
book.set('title', 'My Fifth Book');
book.set('author', author);
book.save().then((book) => {
  // Find all the books by the same author
  const query = new AV.Query('Book');
  query.equalTo('author', author);
  query.find().then((books) => {
    // books is an array of Book objects by the same author
  });
});

Security of User Objects

The AV.User class is secured by default. You are not able to invoke any save- or delete-related methods unless the AV.User was obtained using an authenticated method like logIn or signUp. This ensures that each user can only update their own data.

The reason behind this is that most data stored in AV.User 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:

const user = AV.User.logIn('Tom', 'cat!@#123').then((user) => {
  // Attempt to change username
  user.set('username', 'Jerry');
  // Password is hashed and an empty string will be returned
  const password = user.get('password');
  // Save changes
  user.save().then((user) => {
    // This will work since the user is authenticated

    // Get the user with a non-authenticated method
    const query = new AV.Query('_User');
    query.get(user.objectId).then((unauthenticatedUser) => {
      unauthenticatedUser.set('username', 'Toodle');
      unauthenticatedUser.save().then((unauthenticatedUser) => { }, (error) => {
        // This will cause error since the user is unauthenticated
      });
    });
  });
});

The AV.User obtained from AV.User.current() will always be authenticated.

To check if AV.User is authenticated, you can invoke the isAuthenticated method. You do not need to check if AV.User 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 AV.ACL 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:

const authData = {
  // Required
  uid:           'UID',
  access_token:  'ACCESS_TOKEN',

  // Optional
  extra_key: 'content'
};
AV.User.loginWithAuthData(authData, 'github').then((user) => {
  // Logged in successfully
}, (error) => {
  // Failed to log in
});

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 AV.User 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.

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:

user.associateWithAuthData(githubData, "github").then(function(user) {
  // linked
}).catch(function(error) {
  console.error("error: ", error);
});

Unlinking

Similarly, a third-party account can be unlinked.

For example, the code below unlinks a user's GitHub account:

```js
user.dissociateAuthData('github').then((s) => {
  // unlinked
}, (error) => {
  // failed to unlink
});

Anonymous Users

With the support of anonymous users, you can have your users try the application without signing up or logging in. The code below creates an anonymous user:

AV.User.loginAnonymously().then((user) => {
  // user is the new anonymous user
});

You can add new properties or fields to an anonymous user just like with a normal user, such as username, password, email, etc. You can also convert an anonymous user to a normal user by going through the same sign-up process as you do with a normal user. An anonymous user can:

• Sign up with username and password.
• Link to a third-party service or platform, such as GitHub.

The code below sets a username and password for an anonymous user:

// currentUser is the anonymous user
const currentUser = AV.User.current();

user.setUsername('Tom');
user.setPassword('cat!@#123');

user.signUp().then((user) => {
  // currentUser has become a normal user
}, (error) => {
  // Sign-up failed (often because the username is already taken)
});

The code below checks if the current user is anonymous:

const currentUser = AV.User.current();
if (currentUser.isAnonymous()) {
  // currentUser is anonymous
} else {
  // currentUser is not anonymous
}

If an anonymous user is not converted to a normal user before they log out, they will not be able to log in to the same account later and the data stored in that account cannot be retrieved anymore.

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.

Push Notifications

You can send notifications to mobile devices in JavaScript SDK.

For example, to send push notifications to all devices subscribed to the public channel:

AV.Push.send({
  channels: [ 'public' ],
  data: {
    alert: 'public message'
  }
});

Here is another example sending a push notification to a specific user:

const query = new AV.Query('_Installation');
query.equalTo('installationId', installationId);
AV.Push.send({
  where: query,
  data: {
    alert: 'Public message'
  }
});

Please refer to the JavaScript SDK API Documentation and the Push Notifications Guide for more information.

WebView

LeanStorage JavaScript SDK can be used in a WebView like PhoneGap, Cordova, WeChat WebView, etc.

Android WebView

If you are using Android WebView, the following configurations need to be done when creating WebView in your Native code.

1. Our JS SDK uses window.localStorage which means that localStorage of WebView needs to be enabled:

   yourWebView.getSettings().setDomStorageEnabled(true);
   

2. If you wish to debug WebView directly in your mobile devices, remote debugging needs to be configured for generating WebView. Refer to Google's official documentation for more details.

   if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
     yourWebView.setWebContentsDebuggingEnabled(true);
   }
   

   Keep in mind that this method is only supported on Android 4.4 and above.

3. When developing the UI of your app with WebView, Native makes use of Hybrid for the app running on your phone. We recommend that you first design the UI of your app with Chrome Developer Tools. After the UI is done, start working on data binding with Native during which you can debug WebView on your phone with Remote debugger. This will save you a lot of time on developing and debugging. If you choose to develop UI with Remote debugger as well, you will end up spending more time on it.

4. As a security practice to prevent JavaScript from calling Java functions for accessing the file system of an Android device, Android 4.2 and later versions only allow WebView to access the methods exposed by the annotation @JavascriptInterface. If you have users using Android 4.2 or above, make sure the annotation is added or Uncaught TypeError might be triggered.