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RealmProvider (@realm/react)

On this page

  • Props
  • Configure a Realm with RealmProvider
  • Configure More Than One Realm
  • RealmProvider Hooks
  • useRealm()
  • useObject()
  • useQuery()
  • Create Context with createRealmContext()
Type signature
RealmProvider(props, context?): null | ReactElement<any, any>

Components nested within RealmProvider can access the configured realm and use the RealmProvider hooks.

All properties of BaseConfiguration can be passed as props.

RealmProvider has more props that define its behavior:

  • fallback?: React.ComponentType<unknown> | React.ReactElement | null | undefined

    The fallback component to render while the Realm is opening.

  • closeOnUnmount?: boolean

    Default is true. If set to false, realm will not close when the component unmounts.

  • realmRef?: React.MutableRefObject<Realm | null>

    A ref to the realm instance. This is useful if you need to access the realm instance outside of the scope of the realm.

  • children: React.ReactNode

You can configure a RealmProvider in two ways:

  • Import RealmProvider directly from @realm/react

  • Use createRealmContext() to configure a RealmProvider and create hooks

This section details how to configure a RealmProvider imported directly from @realm/react. For information about using createRealmContext(), refer to Create Context with createRealmContext().

Object models are part of most realm configurations. To learn more about Realm and data models, refer to Define a Realm Object Model.

When you import RealmProvider from @realm/react, that Provider has a specific context and is associated with a single realm. If you need to configure more than one realm, use createRealmContext() to instantiate a new Provider for each realm.

If you import useRealm(), useQuery(), or useObject() directly from @realm/react, those hooks use the default realm context. To work with more than one realm, you need to destructure a new realm Provider and its associated hooks from the result of createRealmContext(). You should namespace providers to avoid confusion about which Provider and hooks you're working with.

For a detailed guide, refer to Expose More Than One Realm.

For details about createRealmContext(), refer to "Create Context with createRealmContext()" on this page.

Type signature
useRealm(): Realm

The useRealm() hook returns an opened realm instance. The realm instance gives you access to realm methods and properties. For example, you can call realm.write() to add a realm object to your realm.

To learn more about modifying Realm data, refer to Write Transactions.

const CreatePersonInput = () => {
const [name, setName] = useState('');
const realm = useRealm();
const handleAddPerson = () => {
realm.write(() => {
realm.create('Person', {_id: PERSON_ID, name: name, age: 25});
});
};
return (
<>
<TextInput value={name} onChangeText={setName} />
<Button
onPress={() => handleAddPerson()}
title='Add Person'
/>
</>
);
};

Returns

  • Realm Returns a realm instance. This is the realm created by the hook's parent, RealmProvider.

Type signature
useObject<T>(type, primaryKey): T & Realm.Object<T> | null

The useObject() hook returns a Realm object for a given primary key. You can pass an object class 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 rerender the component using the hook on any change to the object.

const TaskItem = ({_id}: {_id: number}) => {
const myTask = useObject(Task, _id);
return (
<View>
{myTask ? (
<Text>
{myTask.name} is a task with the priority of: {myTask.priority}
</Text>
) : null}
</View>
);
};

Parameters

  • type: string A string that matches your object model's class name or a reference to a class that extends Realm.Object.

  • primaryKey: T[keyof T] The primary key of the desired object.

Returns

  • Realm.Object | null A Realm Object or null if no object is found.

Type signature
useQuery<T>(type, query?, deps?): Realm.Results<T & Realm.Object<T>>

The useQuery() hook returns a collection of realm objects of a given type. These are the results of your query. A query can be an object class or the class name as a string.

The useQuery() method subscribes to updates to any objects in the collection and rerenders the component using it on any change to the results.

You can use .filtered() and .sorted() to filter and sort your query results. You should do this in the query argument of useQuery so that they only run when there are changes in the dependency array. For more examples, refer to the CRUD - Read docs.

const TaskList = () => {
const [priority, setPriority] = useState(4);
// filter for tasks with a high priority
const highPriorityTasks = useQuery(
Task,
tasks => {
return tasks.filtered('priority >= $0', priority);
},
[priority],
);
// filter for tasks that have just-started or short-running progress
const lowProgressTasks = useQuery(Task, tasks => {
return tasks.filtered(
'$0 <= progressMinutes && progressMinutes < $1',
1,
10,
);
});
return (
<>
<Text>Your high priority tasks:</Text>
{highPriorityTasks.map(taskItem => {
return <Text>{taskItem.name}</Text>;
})}
<Text>Your tasks without much progress:</Text>
{lowProgressTasks.map(taskItem => {
return <Text>{taskItem.name}</Text>;
})}
</>
);
};

Parameters

  • type: string A string that matches your object model's class name or a reference to a class that extends Realm.Object.

  • query?: QueryCallback<T> A query function that can filter and sort query results. Builds on useCallback to memoize the query function.

  • deps?: DependencyList A list of query function dependencies that's used to memoize the query function.

Returns

  • Realm.Results<T> A Realm Object or null if no object is found.

Type signature
createRealmContext(realmConfig?): RealmContext

Most of the time, you will only use createRealmContext() if you need to configure more than one realm. Otherwise, you should import RealmProvider and hooks directly from @realm/react.

The createRealmContext() method creates a React Context object for a realm with a given Configuration. The Context object contains the following:

  • A Context Provider (referred to as RealmProvider elsewhere) component that wraps around child components and provides them with access to hooks.

  • Various prebuilt Hooks that access the configured realm.

For a detailed guide, refer to Expose More Than One Realm.

Parameters

Returns

  • RealmContext An object containing a RealmProvider component, and the useRealm, useQuery and useObject hooks.

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