Use Realm React
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Overview
Realm React is an npm package that provides an easy-to-use API to perform common Realm operations, such as querying or writing to a realm and listening to realm objects.
Realm React helps you avoid creating boilerplate code, such as creating your own listeners and state management. Realm React provides access to Realm database through a set of hooks that update React state when the Realm data changes. This means that components using these hooks will re-render on any changes to data in the realm.
Note
Using Realm React with Realm JS Version 11
To use Realm JS version 11.0.0 or higher with Realm React, you must upgrade to version 0.4.0 or higher.
Setup Realm React
To set up Realm React, you can either start from scratch with a new application using the Realm Expo template or install Realm React for an existing React Native application.
Create a Realm Context
The createRealmContext()
method creates a React Context object for a realm with a given Realm.Configuration. The Context
object contains the
following:
A Context Provider component that wraps around a component and provides any of its child components with access to the hooks.
Various pre-built Hooks that you can use to access the opened realm, query the realm, etc.
Setup
We recommend creating a file where you will define a Realm object type, a Realm
configuration, and create a Realm Context
. At the top of the file, import
Realm and the createRealmContext()
method.
import {Realm, createRealmContext} from '@realm/react';
Next, define a Object Schema using a JavaScript class. The Task
class below contains the following:
A
generate()
method that returns aTask
insertion object that automatically sets computed values, such as_id
andcreatedAt
. This insertion can be forwarded torealm.create
to perform an insertionA
schema
property that defines this Object Schema. Read the Define a Realm Object Schema documentation to learn more.
export class Task extends Realm.Object { _id!: Realm.BSON.ObjectId; description!: string; isComplete!: boolean; createdAt!: Date; // the Task.generate() method creates Task objects with fields with default values static generate(description: string) { return { _id: new Realm.BSON.ObjectId(), description, isComplete: false, createdAt: new Date(), }; } // To use a class as a Realm object type, define the object schema on the static property "schema". static schema = { name: 'Task', primaryKey: '_id', properties: { _id: 'objectId', description: 'string', isComplete: {type: 'bool', default: false}, createdAt: 'date', }, }; }
Finally, create a Realm.Configuration
object and set its schema
property
to the classes you have created. Pass the configuration object to the
createRealmContext()
method. Export the return value of
createRealmContext()
, so you can use the Context
object in other files.
const config = { schema: [Task], }; export default createRealmContext(config);
Using the Realm Provider
Wrap the component needing access to Realm Database, typically the top layer
of your application, with the RealmProvider
component included in the
Context
object, which was returned from createRealmContext
. The
RealmProvider
provides child components access to the configured
Realm through the hooks included in the Context
object.
Tip
Choosing Which Components to Wrap inside the Realm Provider
For simple use-cases, you may want to wrap your entire application in the
RealmProvider
component, such as the example below. For additional security,
you may only want to give access to the opened realm to specific screens, or
after the user has logged-in.
Usage
Import the Context
object that you created. In the example below, the
Context
object is called TaskContext
since it refers to the Realm Context
of
the Task. You can Destructure
the TaskContext
object to get its RealmProvider
.
import TaskContext from './models/Task'; const {RealmProvider} = TaskContext;
Wrap the RealmProvider
around the component that you want
to give access to the configured realm. In the example below, we give the entire
app access to the realm by wrapping the RealmProvider
around
the App
component, which renders the application.
function AppWrapper() { return ( <RealmProvider> <App /> </RealmProvider> ); }
Dynamically Update the Realm Configuration
You can dynamically update the Realm configuration by setting
props on the RealmProvider
component. The props you set on the RealmProvider
will overwrite any
property passed into createRealmContext()
.
In the following example, we update the RealmProvider with a sync
configuration and a fallback
property that is used to render a temporary LoadingSpinner
component while
waiting for Device Sync to open:
function AppWrapper() { const syncConfig = { user: app?.currentUser, partitionValue: 'ExpoTemplate', }; return ( <RealmProvider sync={syncConfig} fallback={() => <LoadingSpinner />}> <App /> </RealmProvider> ); }
Use Realm Provider Hooks
Once you have wrapped your component with your RealmProvider
, your component
and its child components will have access to the useRealm()
,
useObject()
, and useQuery()
hooks.
Import the Task
model and Context
object that you created. In the example below, the
Context
object, called TaskContext
, refers to the Context
of
the Task. Destructure
the TaskContext
object to get its hooks.
import TaskContext, {Task} from './models/Task'; const {useRealm, useQuery, useObject} = TaskContext;
useRealm
The useRealm()
hook returns the opened realm instance.
The handleAddTask()
method of the App
component writes to the realm
returned by the useRealm()
hook in the following example.
const realm = useRealm(); const handleAddTask = useCallback( (description: string): void => { if (!description) { return; } realm.write(() => { realm.create('Task', Task.generate(description)); }); }, [realm], );
The Realm.create() call invokes the Task.generate()
method defined in the Task
class. This method instantiates
a JavaScript object with default values for the _id
, isComplete
, and
createdAt
properties.
Tip
See also:
Read the Write Transactions documentation to learn more about modifying Realm data.
useObject
The useObject()
hook returns a Realm object for a given
primary key. You can invoke it with the class
model definition (this will add types to the returned object in TypeScript) or
the class name as a string and the primary key. The useObject()
method
returns null if the object doesn't exist or you have deleted it. The hook will
automatically subscribe to updates and re-render the component using the hook on
any change to the object.
In the following example, the useObject()
hook retrieves a Task
object,
and its description is rendered in the UI.
const SampleTask = ({_id}) => { const myTask = useObject(Task, _id); return ( <View> <Text>Task: {myTask?.description} </Text> </View> ); };
useQuery
The useQuery()
hook returns a collection of realm objects of a given type.
Like useObject
, it is either invoked with the Object Schema class or the model
name as a string. The useQuery()
method subscribes to updates to any
objects in the collection and re-renders the component using it on any change to the query results.
In the following example, of a TaskList
component, The Task
class is passed to the useQuery()
and the tasks are set as a data
prop
of a FlatList component.
function TaskList({onToggleTaskStatus, onDeleteTask}) { const tasks = useQuery(Task); return ( <View style={styles.listContainer}> <FlatList data={tasks} keyExtractor={task => task._id.toString()} renderItem={({item}) => ( <TaskItem description={item.description} isComplete={item.isComplete} onToggleStatus={() => onToggleTaskStatus(item)} onDelete={() => onDeleteTask(item)} /> )} /> </View> ); }
Tip
To learn how to render a filtered or sorted list of tasks, read the CRUD - Read docs.
Using the App Provider
To use Realm features such as authentication and sync, use the
AppProvider
to initiate a new Realm.App. Wrap the
AppProvider
outside of the RealmProvider
and any components which need
access to the useApp hook.
import { AppProvider } from '@realm/react' function AppWrapper() { return ( <AppProvider id={appId}> <RealmProvider> <App /> </RealmProvider> </AppProvider> ); }
useApp
The useApp()
hook provides access to the Realm.App
instance.
In the following example, we call useApp()
within a LoginComponent
, and
then use the app instance to log in with email/password authentication.
import {useApp} from '@realm/react'; function LoginComponent({}) { const [email, setEmail] = useState(''); const [password, setPassword] = useState(''); const app = useApp(); const signIn = async () => { const credentials = Realm.Credentials.emailPassword(email, password); await app.logIn(credentials); }; // ... }
Using the User Provider
The UserProvider
provides a Realm user for its
child components to access.
The UserProvider
:
contains an optional
fallback
property that renders a Login component when the user has not authenticated.renders its child components only if the user is logged in or has no fallback property.
In the following example, we pass a Login component to the fallback property of
UserProvider
. Once the user has logged in, the Login component disappears
from the view, and the App
is rendered. We wrap the App
in a
RealmProvider
with a sync configuration to give the App
access to a
synced realm. If the user logs out, the application falls back to
the Login component.
import { AppProvider, UserProvider } from '@realm/react' const AppWrapper = () => { return ( <AppProvider id={appId}> <UserProvider fallback={LoginComponent}> {/* After login, user will be automatically populated in realm configuration */} <RealmProvider sync={{partitionValue: 'SamplePartition'}}> <App /> </RealmProvider> </UserProvider> </AppProvider> ); };
Note
The User is Automatically Set for the Sync Configuration
When the UserProvider
wraps the RealmProvider
, the RealmProvider
automatically sets the logged-in user for your sync configuration. This means
you do not need to specify your user in your sync configuration object.
useUser
The useUser()
hook provides access to the logged-in user.
In the following example, we call useApp()
within a SampleTask
component and display the logged-in user's _id
.
import {useUser} from '@realm/react'; const SampleTask = ({_id}) => { // Access the logged in user using the useUser hook const user = useUser(); const myTask = useObject(Task, _id); return ( <View> <Text> The task {myTask?.description} was created by user id: {user?.id} </Text> </View> ); };
Summary
You can set up Realm React on an existing application by installing it through npm or on a new application through the Realm Expo template.
A Realm
Context
opens a realm and contains aRealmProvider
and a set of pre-built hooks.A
RealmProvider
provides access to the configured realm using hooks to display and modify data.The pre-built
RealmProvider
hooks provide functionality, including interacting with a realm and finding realm object(s).The
AppProvider
instantiates a new App and provides its child components access to the App instance.You can use the
useApp()
hook to access the instantiated App within child components.The
UserProvider
renders it's child components if the user has logged in and renders a fallback component if the user has not logged in.You can use the
useUser()
hook to gain access to the logged-in user within any child components of theUserProvider
.