Realm React Native enables you to efficiently write your app’s model layer in a safe, persisted and fast way. Here’s what it looks like:

// Define your models and their properties
class Car {}
Car.schema = {
  name: 'Car',
  properties: {
    make:  'string',
    model: 'string',
    miles: 'int',
  }
};
class Person {}
Person.schema = {
  name: 'Person',
  properties: {
    name:    {type: 'string'},
    cars:    {type: 'list', objectType: 'Car'},
    picture: {type: 'data', optional: true}, // optional property
  }
};

// Get the default Realm with support for our objects
let realm = new Realm({schema: [Car, Person]});

// Create Realm objects and write to local storage
realm.write(() => {
  let myCar = realm.create('Car', {
    make: 'Honda',
    model: 'Civic',
    miles: 1000,
  });
  myCar.miles += 20; // Update a property value
});

// Query Realm for all cars with a high mileage
let cars = realm.objects('Car').filtered('miles > 1000');

// Will return a Results object with our 1 car
cars.length // => 1

// Add another car
realm.write(() => {
  let myCar = realm.create('Car', {
    make: 'Ford',
    model: 'Focus',
    miles: 2000,
  });

// Query results are updated in realtime
cars.length // => 2

Getting Started

Follow the installation instructions below to use Realm React Native via npm, or see the source on GitHub.

Prerequisites

• Make sure your environment is set up to run React Native applications. Follow the React Native instructions for getting started.
• Apps using Realm can target both iOS and Android.
• React Native 0.20.0 and later is supported.

Installation

• Create a new React Native project:

  react-native init <project-name>

• Change directories into the new project (cd <project-name>) and add the realm dependency:

  npm install --save realm

• Next use react-native to link your project to the realm native module.

  react-native link realm

You’re now ready to go. To see Realm in action, add the following as the definition for your class <project-name> in index.ios.js or index.android.js:

const Realm = require('realm');

class <project-name> extends Component {
 render() {
   let realm = new Realm({
     schema: [{name: 'Dog', properties: {name: 'string'}}]
   });

   realm.write(() => {
     realm.create('Dog', {name: 'Rex'});
   });

   return (
     <View style={styles.container}>
       <Text style={styles.welcome}>
         Count of Dogs in Realm: {realm.objects('Dog').length}
       </Text>
     </View>
   );
 }
}

You can then run your app on a device and in a simulator!

API Reference

You can consult our full API reference for all classes, methods and more.

Examples

Start by cloning the project from GitHub:

git clone https://github.com/realm/realm-js.git

Then in the cloned directory:

git submodule update --init --recursive

On android you need the NDK installed and to set the ANDROID_NDK environment variable:

export ANDROID_NDK=/usr/local/Cellar/android-ndk/r10e

The React Native examples are in the examples directory. You need to run npm install for each example before running for the first time.

Getting Help

• Need help with your code? Ask on StackOverflow. We actively monitor & answer questions on SO!
• Have a bug to report? Open an issue on our repo. If possible, include the version of Realm, a full log, the Realm file, and a project that shows the issue.
• Have a feature request? Open an issue on our repo. Tell us what the feature should do, and why you want the feature.

If you’re using a crash reporter (like Crashlytics or HockeyApp), make sure to enable log collection. Realm logs metadata information (but no user data) when throwing exceptions and in irrecoverable situations, and these messages can help debug when things go wrong.

Models

Realm data models are defined by the schema information passed into a Realm during initialization. The schema for an object consists of the object’s name and a set of properties each of which has a name and type as well as the objectType for object and list properties. You can also designate each property to be optional or to have a default value.

var Realm = require('realm');

const CarSchema = {
  name: 'Car',
  properties: {
    make:  'string',
    model: 'string',
    miles: {type: 'int', default: 0},
  }
};
const PersonSchema = {
  name: 'Person',
  properties: {
    name:     'string',
    birthday: 'date',
    cars:     {type: 'list', objectType: 'Car'},
    picture:  {type: 'data', optional: true}, // optional property
  }
};

// Initialize a Realm with Car and Person models
let realm = new Realm({schema: [CarSchema, PersonSchema]});

If you’d prefer your objects inherit from an existing class, you just need to define the schema on the object constructor and pass in the constructor when creating a realm:

class Person {
  get ageSeconds() {
    return Math.floor((Date.now() - this.birthday.getTime()));
  }
  get age() {
    return ageSeconds() / 31557600000;
  }
}

Person.schema = PersonSchema;

// Note here we are passing in the `Person` constructor
let realm = new Realm({schema: [CarSchema, Person]});

Once you have defined your object models you can create and fetch objects from the realm:

realm.write(() => {
  let car = realm.create('Car', {
    make: 'Honda',
    model: 'Civic',
    miles: 750,
  });

  // you can access and set all properties defined in your model
  console.log('Car type is ' + car.make + ' ' + car.model);
  car.miles = 1500;
});

Basic Property Types

Realm supports the following basic types: bool, int, float, double, string, data, and date.

• bool properties map to JavaScript Boolean objects
• int, float, and double properties map to JavaScript Number objects. Internally ‘int’ and ‘double’ are stored as 64 bits while float is stored with 32 bits.
• string properties map to String
• data properties map to ArrayBuffer
• date properties map to Date

When specifying basic properties as a shorthand you may specify only the type rather than having to specify a dictionary with a single entry:

const CarSchema = {
  name: 'Car',
  properties: {
    // The following property types are equivalent
    make:   {type: 'string'},
    model: 'string',
  }
}

Object Properties

For object types you specify the name property of the object schema you are referencing:

const PersonSchema = {
  name: 'Person',
  properties: {
    // All of the following property definitions are equivalent
    car: {type: 'Car'},
    van: 'Car',
  }
};

When using object properties you need to make sure all referenced types are present in the schema used to open the Realm:

// CarSchema is needed since PersonSchema contains properties of type 'Car'
let realm = new Realm({schema: [CarSchema, PersonSchema]});

When accessing object properties, you can access nested properties using normal property syntax:

realm.write(() => {
  var nameString = person.car.name;
  person.car.miles = 1100;

  // create a new Car by setting the property to valid JSON
  person.van = {make: 'Ford', model: 'Transit'};

  // set both properties to the same car instance
  person.car = person.van;
});

List Properties

For list properties you must specify the property type as list as well as the objectType:

const PersonSchema = {
  name: 'Person',
  properties: {
    cars: {type: 'list', objectType: 'Car'},
  }
}

When accessing list properties a List object is returned. List has methods very similar to a regular JavaScript array. The big difference is that any changes made to a List are automatically persisted to the underlying Realm. Additionally, Lists belong to the underlying object they were acquired from - you can only get List instances by accessing a property from an owning object and they cannot be manually created.

let carList = person.cars;

// Add new cars to the list
realm.write(() => {
  carList.push({make: 'Honda', model: 'Accord', miles: 100});
  carList.push({make: 'Toyota', model: 'Prius', miles: 200});
});

let secondCar = carList[1].model;  // access using an array index

Optional Properties

Properties can be declared as optional or non-optional by specifying the optional designator in your property definition:

const PersonSchema = {
  name: 'Person',
  properties: {
    name:     {type: 'string'},               // required property
    birthday: {type: 'date', optional: true}, // optional property

    // object properties are always optional
    car:      {type: 'Car'},
  }
};

let realm = new Realm({schema: [PersonSchema, CarSchema]});

realm.write(() => {
  // optional properties can be set to null or undefined at creation
  let charlie = realm.create('Person', {
    name: 'Charlie',
    birthday: new Date(1995, 11, 25),
    car: null,
  });

  // optional properties can be set to `null`, `undefined`,
  // or to a new non-null value
  charlie.birthday = undefined;
  charlie.car = {make: 'Honda', model: 'Accord', miles: 10000};
});

As seen above object properties are always optional and do not need an optional designation. List properties cannot be declared as optional or set to null. You can set or initialize a list with an empty array to clear it.

Default Property Values

Default property values can be specified by setting the default designator in the property definition. To use a default value, leave the property unspecified during object creation.

const CarSchema = {
  name: 'Car',
  properties: {
    make:  {type: 'string'},
    model: {type: 'string'},
    drive: {type: 'string', default: 'fwd'},
    miles: {type: 'int',    default: 0}
  }
};

realm.write(() => {
  // Since `miles` is left out it defaults to `0`, and since
  // `drive` is specified, it overrides the default value
  realm.create('Car', {make: 'Honda', model: 'Accord', drive: 'awd'});
});

Indexed Properties

You can add an indexed designator to a property definition to cause that property to be indexed. This is supported for int, string, and bool property types:

var BookSchema = {
  name: 'Book',
  properties: {
    name: { type: 'string', indexed: true },
    price: 'float'
  }
};

Indexing a property will greatly speed up queries where the property is compared for equality at the cost of slower insertions.

Primary Keys

You can specify the primaryKey property in an object model for string and int properties. Declaring a primary key allows objects to be looked up and updated efficiently and enforces uniqueness for each value. Once an object with a primary key has been added to a Realm the primary key cannot be changed.

const BookSchema = {
  name: 'Book',
  primaryKey: 'id',
  properties: {
    id:    'int',    // primary key
    title: 'string',
    price: 'float'
  }
};

Primary key properties are automatically indexed.

Writes

Write transactions incur non-negligible overhead - you should architect your code to minimize the number of write transactions.

Creating Objects

As shown above, objects are created using the create method:

let realm = new Realm({schema: [CarSchema]);

realm.write(() => {
  realm.create('Car', {make: 'Honda', model: 'Accord', drive: 'awd'});
});

Nested Objects

If an object has object properties, values for those properties can be created recursively by specifying JSON values for each child property:

let realm = new Realm({schema: [PersonSchema, CarSchema]);

realm.write(() => {
  realm.create('Person', {
    name: 'Joe',
    // nested objects are created recursively
    car: {make: 'Honda', model: 'Accord', drive: 'awd'},
  });
});

Updating Objects

Typed Updates

You can update any object by setting its properties within a write transaction.

realm.write(() => {
  car.miles = 1100;
});

Creating and Updating Objects With Primary Keys

If your model class includes a primary key, you can have Realm intelligently update or add objects based off of their primary key values. This is done by passing true as the third argument to the create method:

realm.write(() => {
  // Create a book object
  realm.create('Book', {id: 1, title: 'Recipes', price: 35});

  // Update book with new price keyed off the id
  realm.create('Book', {id: 1, price: 55}, true);
});

In the example above, since an object already exists with the id value of 1 and we have passed in true for the third argument, the price property is updated rather than trying to create a new object. Since the title property is omitted the object retains the original value for this property. Note that when creating or updating objects with primary key properties the primary key must be specified.

Deleting Objects

Objects can be deleted by calling the delete method within a write transaction.

realm.write(() => {
  // Create a book object
  let book = realm.create('Book', {id: 1, title: 'Recipes', price: 35});

  // Delete the book
  realm.delete(book);

  // Delete multiple books by passing in a `Results`, `List`,
  // or JavaScript `Array`
  let allBooks = realm.objects('Book');
  realm.delete(allBooks); // Deletes all books
});

Queries

Queries allow you to get objects of a single type from a Realm, with the option of filtering and sorting those results. All queries (including queries and property access) are lazy in Realm. Data is only read when objects and properties are accessed. This allows you to represent large sets of data in a performant way.

When performing queries you are returned a Results object. Results are simply a view or your data and are not mutable.

The most basic method for retrieving objects from a Realm is using the objects method on a Realm to get all objects of a given type:

let dogs = realm.objects('Dog'); // retrieves all Dogs from the Realm

Filtering

You can get a filtered Results by calling the filtered method with a query string.

For example, the following would change our earlier example to retrieve all dogs with the color tan and names beginning with ‘B’:

let dogs = realm.objects('Dog');
let tanDogs = dogs.filtered('color = "tan" AND name BEGINSWITH "B"');

At the moment only a subset of the NSPredicate syntax is supported in the query language. Basic comparison operators ==, !=, >, >=, <, and <= are supported for numeric properties. ==, BEGINSWITH, ENDSWITH, and CONTAINS are supported for string properties. String comparisons can be made case insensitive by appending [c] to the operator: ==[c], BEGINSWITH[c] etc. Filtering by properties on linked or child objects can by done by specifying a keypath in the query eg car.color == 'blue'.

Sorting

Results allows you to specify a sort criteria and order based on a single or multiple properties. For example, the following call sorts the returned cars from the example above numerically by miles:

let hondas = realm.objects('Car').filtered('make = "Honda"');

// Sort Hondas by mileage
let sortedHondas = hondas.sorted('miles');

Auto-Updating Results

Results instances are live, auto-updating views into the underlying data, which means results never have to be re-fetched. Modifying objects that affect the query will be reflected in the results immediately.

let hondas = realm.objects('Car').filtered('make = "Honda"');
// hondas.length == 0

realm.write(() => {
  realm.create('Car', {make: 'Honda', model: 'RSX'});
});
// hondas.length == 1

This applies to all Results instances, included those returned by the objects, filtered, and sorted methods.

This property of Results not only keeps Realm fast and efficient, it allows your code to be simpler and more reactive. For example, if your view relies on the results of a query, you can store the Results in a property and access it without having to make sure to refresh its data prior to each access.

You can subscribe to change events to know when Realm data is updated, indicating when your app’s UI should be refreshed for example, without having to re-fetch your Results.

Limiting Results

Most other database technologies provide the ability to ‘paginate’ results from queries (such as the ‘LIMIT’ keyword in SQLite). This is often done out of necessity to avoid reading too much from disk, or pulling too many results into memory at once.

Since queries in Realm are lazy, performing this sort of paginating behavior isn’t necessary at all, as Realm will only load objects from the results of the query once they are explicitly accessed.

If for UI-related or other implementation reasons you require a specific subset of objects from a query, it’s as simple as taking the Results object, and reading out only the objects you need.

let cars = realm.objects('Car');

// get first 5 Car objects
let firstCars = cars.slice(0, 5);

Realms

Multiple Realms

It’s sometimes useful to have multiple Realms persisted at different locations. For example, you may want to bundle some data with your application in a Realm file, in addition to your main Realm. You can do this by specifying the path argument when initializing your realm. All paths are relative to the writable documents directory for your application:

// Open a realm at another path
let realmAtAnotherPath = new Realm({
  path: 'anotherRealm.realm',
  schema: [CarSchema]
});

Default Realm Path

You may have noticed in all previous examples that the path argument has been omitted. In this case the default Realm path is used. You can access and change the default Realm path using the Realm.defaultPath global property.

Schema Version

The last option available when opening a Realm is the schemaVersion property. When omitted, the schemaVersion property defaults to 0. You are required to specify the schemaVersion when initializing an existing Realm with a schema that contains objects that differ from their previous specification. If the schema was updated and the schemaVersion was not, an exception will be thrown.

const PersonSchema = {
  name: 'Person',
  properties: {
    name: 'string'
  }
};

// schemaVersion defaults to 0
let realm = new Realm({schema: [PersonSchema]});

const UpdatedPersonSchema = {
  // The schema name is the same, so previous `Person` object
  // in the Realm will be updated
  name: 'Person',
  properties: {
    name: 'string',
    dog:  'Dog'     // new property
  }
};

// this will throw because the schema has changed
// and `schemaVersion` is not specified
let realm = new Realm({schema: [UpdatedPersonSchema]});

// this will succeed and update the Realm to the new schema
let realm = new Realm({schema: [UpdatedPersonSchema], schemaVersion: 1});

If you wish to retrieve the current schema version of a Realm, you may do so with the Realm.schemaVersion method.

let currentVersion = Realm.schemaVersion(Realm.defaultPath);

Migrations

When working with a database your data model will most likely change over time. For example, suppose we have the following Person model:

var PersonSchema = {
  name: 'Person',
  properties: {
    firstName: 'string',
    lastName: 'string',
    age: 'int'
  }
}

We want to update the data model to require a name property, rather than separate first and last names. To do this, we simply change the schema to the following:

var PersonSchema = {
  name: 'Person',
  properties: {
    name: 'string',
    age: 'int'
  }
}

At this point if you had saved any data with the previous model version there will be a mismatch between the new code and the old data Realm has stored on disk. When this occurs, an exception will be thrown when you try to open the existing Realm with the new schema unless you run a migration.

Performing a Migration

You define a migration and the associated schema version by updating the schemaVersion and defining an optional migration function. Your migration function provides any logic needed to convert data models from previous schemas to the new schema. When opening a Realm the migration function will be applied to update the Realm to the given schema version only if a migration is needed.

If no migration function is supplied then any new properties an automatically added and old properties are removed from the database when updating to the new schemaVersion. If you need to update old or populate new properties when upgrading your version you can do this in the migration function. For example, suppose we want to migrate the Person model declared earlier. You can populate the name property of the new schema using the old firstName and lastName properties:

var realm = new Realm({
  schema: [PersonSchema],
  schemaVersion: 1,
  migration: function(oldRealm, newRealm) {
    // only apply this change if upgrading to schemaVersion 1
    if (oldRealm.schemaVersion < 1) {
      var oldObjects = oldRealm.objects('Person');
      var newObjects = newRealm.objects('Person');

      // loop through all objects and set the name property in the new schema
      for (var i = 0; i < oldObjects.length; i++) {
        newObjects[i].name = oldObjects[i].firstName + ' ' + oldObjects[i].lastName;
      }
    }
  }
});

var fullName = realm.objects('Person')[0].name;

Once the migration is successfully completed the Realm and all of its objects can be accessed as usual by your app.

Linear Migrations

With the migration pattern described above you can potentially run into issues when migrating over multiple versions. This could happen if a user skips an app update and a property has been changed multiple times in the versions being skipped. In this case you may need to edit old migration code to correctly update data from old schema to the latest schema.

It’s possible to avoid this issue by running multiple migrations sequentially, making sure that the database is upgraded to each previous version and that the associated migration code is run. When following this pattern old migration code should never have to be modified, although you will need to keep all old schema and migration blocks for future use. An example of what this would look like:

var schemas = [
  { schema: schema1, schemaVersion: 1, migration: migrationFunction1 },
  { schema: schema2, schemaVersion: 2, migration: migrationFunction2 },
  ...
]

// the first schema to update to is the current schema version
// since the first schema in our array is at
var nextSchemaIndex = Realm.schemaVersion(Realm.defaultPath);
while (nextSchemaIndex < schemas.length) {
  var migratedRealm = new Realm(schemas[nextSchemaIndex++]);
  migratedRealm.close();
}

// open the Realm with the latest schema
var realm = new Realm(schemas[schemas.length-1]);

Change Events

Change events are sent out when write transactions are completed. To register for change events:

// Observe Realm Change Events
realm.addListener('change', () => {
  // Update UI
  ...
});

// Unregister all listeners
realm.removeAllListeners();

React Native ListView

If you’d like to use List or Results instances as data for a ListView, it is highly recommended that you use the ListView and ListView.DataSource provided by the realm/react-native module:

import { ListView } from 'realm/react-native';

The API is exactly the same as React.ListView, so you can refer to the ListView documentation for usage information.

Encryption

Realm supports encrypting the database file on disk with AES-256+SHA2 by supplying a 64-byte encryption key when creating a Realm.

var key = new Int8Array(64);  // pupulate with a secure key
var realm = new Realm({schema: [CarObject], encryptionKey: key});

// Use the Realm as normal
var dogs = realm.objects('Car');

This makes it so that all of the data stored on disk is transparently encrypted and decrypted with AES-256 as needed, and verified with a SHA-2 HMAC. The same encryption key must be supplied every time you obtain a Realm instance.

There is a small performance hit (typically less than 10% slower) when using encrypted Realms.

The Realm Mobile Platform

The Realm Mobile Platform extends the Realm Mobile Database across the network, enabling automatic synchronization of data across devices.

Enabling this for React Native is in the works!

Troubleshooting

Crash Reporting

We encourage you to use a crash reporter in your application. Many Realm operations could potentially fail at runtime (like any other disk IO), so collecting crash reports from your application will help identify areas where either you (or us) can improve error handling and fix crashing bugs.

Most commercial crash reporters have the option of collecting logs. We strongly encourage you to enable this feature. Realm logs metadata information (but no user data) when throwing exceptions and in irrecoverable situations, and these messages can help debug when things go wrong.

Reporting Realm Issues

If you’ve found an issue with Realm, please either file an issue on GitHub or email us at help@realm.io with as much information as possible for us to understand and reproduce your issue.

The following information is very useful to us:

1. Goals.
2. Expected results.
3. Actual results.
4. Steps to reproduce.
5. Code sample that highlights the issue (full working projects that we can compile ourselves are ideal).
6. Version of Realm.
7. Crash logs & stack traces. See Crash Reporting above for details.