Realm React

A better way to use Realm with React Native applications.

Introduction

Setting up Realm in a React Native application has historically been complex. Re-rendering of components when objects in the database change requires manually adding and removing listeners, which produce a lot of boilerplate code and is error-prone (if listeners properly removed on unmount). This library alleviates that by providing React hooks which return Realm data that is state aware. As a consequence, any change to the Realm data will cause components using the hook to re-render.

Installation

This library requires react-native >= 0.59 and realm >= 10.0.0

npm:

npm install @realm.io/react

yarn:

yarn add @realm.io/react

Usage

Setup the RealmContext and Provider

Create a Realm context object with createRealmContext. It takes a Realm configuration and returns a RealmProvider and contextual hooks.

// realm.ts
import {createRealmContext} from '@realm.io/react';

class Task extends Realm.Object {
  _id!: Realm.BSON.ObjectId;
  description!: string;
  isComplete!: boolean;

  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'
    },
  };
}

export default createRealmContext({schema: [Task]});

Wrap the component needing access to Realm (possibly your entire application) with the RealmProvider componenet. The RealmProvider also accepts Realm configuration properties.

import RealmContext from './realm';

const {RealmProvider} = RealmContext

function AppWrapper() {
  return (
    <RealmProvider>
      <App />
    </RealmProvider>
  );
};

Implement Hooks in Child Components

The hooks created by createRealmContext can now be used by any child component.

import RealmContext from './realm';

const {useRealm, useQuery, useObject} = RealmContext

function MyComponent({someId}){
  const realm = useRealm();
  const tasks = useQuery(Task);
  const someObject = useObject<SomeObject>('Objects', someId);

  // sort collection with useMemo
  const sortedTasks = useMemo( () => tasks.sorted("createdAt"), [tasks])

  // make sure the data is there
  if(!sortedTasks || !someObject){
    return null
  }

  return ...
}

Dynamically Updating a Realm Configuration

It is possible to update the realm configuration by setting props on the RealmProvider. The RealmProvider takes props for all possible realm configuration properties.

For example, one could setup the sync configuration based on a user state:

const [user, setUser] = useState()

//... some logic to get user state

<RealmProvider sync={user, parition}>