Use Realm React

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 a Task insertion object that automatically sets computed values, such as _id and createdAt. This insertion can be forwarded to realm.create to perform an insertion

• A 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);

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>
  );
}

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.

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>
  );
}

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);
  };
  // ...
}

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>
  );
};