react-native-firebase/docs/database/usage/index.md

---
title: Realtime Database
description: Installation and getting started with Realtime Database.
icon: //static.invertase.io/assets/firebase/realtime-database.svg
next: /database/offline-support
previous: /crashlytics/crash-reports
---

# Installation

This module requires that the `@react-native-firebase/app` module is already setup and installed. To install the "app" module, view the
[Getting Started](/) documentation.

```bash
# Install & setup the app module
yarn add @react-native-firebase/app

# Install the database module
yarn add @react-native-firebase/database

# If you're developing your app using iOS, run this command
cd ios/ && pod install && cd ..
```

If you're using an older version of React Native without autolinking support, or wish to integrate into an existing project,
you can follow the manual installation steps for [iOS](/database/usage/installation/ios) and [Android](/database/usage/installation/android).

# What does it do

The Realtime Database is a cloud-hosted database. Data is stored as JSON and synchronized in realtime to every connected
client. React Native Firebase provides native integration with the Android & iOS Firebase SDKs, supporting both realtime
data sync and offline capabilities.

<Youtube id="U5aeM5dvUpA" />

To learn more, view the [Firebase Realtime Database documentation](https://firebase.google.com/docs/database?utm_source=invertase&utm_medium=react-native-firebase&utm_campaign=database).

# Usage

## References

A core concept to understanding Realtime Database are references - a reference to a specific node within your database. A node
can be a specific property or sub-nodes.

To create a [`Reference`](/reference/database/reference), call the `ref` method:

```js
import database from '@react-native-firebase/database';

const reference = database().ref('/users/123');
```

## Reading data

The Realtime Data provides the ability to read the value of a reference as a one-time read, or realtime changes to the node.
When a value is read from the database, the API returns a [`DataSnapshot`](/reference/database/datasnapshot).

The snapshot includes information such as whether the reference node exists, it's value or any children the node has and more.

### One-time read

To read the value once, call the `once` method on a reference:

```js
import database from '@react-native-firebase/database';

database()
  .ref('/users/123')
  .once('value')
  .then(snapshot => {
    console.log('User data: ', snapshot.val());
  });
```

### Realtime changes

To setup an active listener to react to any changes to the node and it's children, call the `on` method with an event handler:

```js
import database from '@react-native-firebase/database';

database()
  .ref('/users/123')
  .on('value', snapshot => {
    console.log('User data: ', snapshot.val());
  });
```

The event handler will be called straight away with the snapshot data, and further called when any changes to the node
occur.

The event handler also returns a function, allowing you to unsubscribe from events. This can be used within any `useEffect`
hooks to automatically unsubscribe when the hook needs to unsubscribe itself:

```jsx
import React, { useEffect } from 'react';
import database from '@react-native-firebase/database';

function User({ userId }) {
  useEffect(() => {
    const subscriber = database();
    ref(`/users/${userId}`).on('value', snapshot => {
      console.log('User data: ', snapshot.val());
    });

    // Stop listening for updates when no longer required
    return () => subscriber();
  }, [userId]);
}
```

#### Additional events

The above example demonstrates how to subscribe to events whenever a value within the node changes. In some cases, you
may need to only subscribe to events whenever a child node is added/changed/moved/removed. This can be achieved by passing
a different [`EventType`](/reference/database/eventtype) to the `on` method.

If you are listening to a node with many children, only listening to data you care about helps reduce network bandwidth
and speeds up your application.

```jsx
import React, { useEffect } from 'react';
import database from '@react-native-firebase/database';

function User({ userId }) {
  useEffect(() => {
    const subscriber = database();
    ref('/users').on('child_added', snapshot => {
      console.log('A new node has been added', snapshot.val());
    });

    // Stop listening for updates when no longer required
    return () => subscriber();
  }, [userId]);
}
```

### Querying

Realtime Database provides support for basic querying of your data. When a reference node contains children, you can both
order & limit the returned results.

If your application requires more advanced query capabilities, it is recommended you use [Cloud Firestore](/firestore).

#### Ordering

By default, results are ordered based on the node [keys](#database-keys). If however you are using custom keys you can use
one of the `orederByX` methods to order your data.

For example, if all of the nodes children are scalar values (string, number or boolean) you can use the `orderByValue` method,
and Firebase will automatically order the results. The example below would return the `def` node before the `abc` node:

```js
/*
 * {
 *   'scores': {
 *     'abc: 30,
 *     'def': 50,
 *   }
 * }
 */

const scores = database()
  .ref('scores')
  .orderByValue()
  .once('value');
```

Please note that the ordering will not be respected if you do not use the `forEach` method provided on the `DataSnapshot`.

#### Limiting

You can limit the number of results returned from a query by using one of the `limitToX` methods. For example, to limit to the
first 10 results:

```js
const users = database()
  .ref('users')
  .limitToFirst(10)
  .once('value');
```

Firebase also provides the ability to return the last set of results in a query via the `limitToLast` method.

Instead of limiting to a specific number of documents, you can also start from, or end at a specific reference node value:

```js
await database()
  .ref('users')
  .orderByChild('age')
  .startAt(21)
  .once('value');
```

## Writing data

The [Firebase documentation](https://firebase.google.com/docs/database/web/structure-data) provides great examples on best
practices on how to structure your data. We highly recommend reading the guide before building out your database.

### Setting data

The `set` method on a [`Reference`](/reference/database/reference) overwrites all of the existing data at that reference node.
The value can be anything; a string, number, object etc:

```js
import database from '@react-native-firebase/database';

database()
  .ref('/users/123')
  .set({
    name: 'Ada Lovelace',
    age: 31,
  })
  .then(() => console.log('Data set.'));
```

If you set the value to `null`, Firebase will automatically class the node as removed, and delete it from the database.

### Updating data

Rather than overwriting all existing data, the `update` method provides the ability to update any existing data on the reference node.
Firebase will automatically merge the data depending on what currently exists.

```js
import database from '@react-native-firebase/database';

database()
  .ref('/users/123')
  .update({
    age: 32,
  })
  .then(() => console.log('Data updated.'));
```

### Pushing data

Currently the examples have only demonstrated working with known reference node keys (e.g. `/users/123`). In some cases,
you may not have a suitable id or may want Firebase to automatically create a node with a generated key. The `push` method
returns a [`ThenableReference`](/reference/database/thenablereference), allowing you to observe a node before it is
sent to remote Firebase database.

The `push` method will automatically generate a new key if one is not provided:

```js
const newReference = database()
  .ref('/users')
  .push();

console.log('Auto generated key: ', newReference.key);

newReference
  .set({
    age: 32,
  })
  .then(() => console.log('Data updated.'));
```

The keys generated are ordered to the current time, so the list of items returned from Firebase will be chronologically
sorted by default.

## Removing data

To remove data, you can call the `remove` method on a reference:

```js
await database()
  .ref('/users/123')
  .remove();
```

Optionally, you can also set the value of a reference node to `null` to remove it from the database:

```js
await database()
  .ref('/users/123')
  .set(null);
```

## Transactions

Transactions are a way to always ensure a write occurs with the latest information available on the server. Transactions never
partially apply writes & all writes execute at the end of a successful transaction.

Imagine a scenario whereby an app has the ability to "Like" user posts. Whenever a user presses the "Like" button,
the `/likes/:postId` value (number of likes) on the database increments. Without transactions, we'd first need to
read the existing value and then increment that value in two separate operations.

On a high traffic application, the value on the server could already have changed by the time the operation sets a new value,
causing the actual number to not be consistent.

Transactions remove this issue by atomically updating the value on the server. If the value changes whilst the transaction
is executing, it will retry. This always ensures the value on the server is used rather than the client value.

To execute a new transaction, call the `transaction` method on a reference:

```js
import database from '@react-native-firebase/database';

function onPostLike(postId) {
  const reference = database().ref(`/likes/${postId}`);

  // Execute transaction
  return reference.transaction(currentLikes => {
    if (currentLikes === null) return 1;
    return currentLikes + 1;
  });
}

// When post "567" is liked
onPostLike('567').then(transaction => {
  console.log('New post like count: ', transaction.snapshot.val());
});
```

Once the transaction is successful, a promise is resolved with a value containing whether the operation committed on the remote
database and the new [`DataSnapshot`](/reference/database/datasnapshot) containing the new value.

# Securing data

It is important that you understand how to write rules in your Firebase console to ensure that your data is secure.
Please follow the Firebase Realtime Database documentation on [security](https://firebase.google.com/docs/database/security)

# Using a secondary database

If the default installed Firebase instance needs to address a different database within the same project, call the database method on the default app with passing the database URL.
For example:

```js
import { firebase } from '@react-native-firebase/database';

const database = firebase.app().database('https://path-to-database.firebaseio.com');

database.ref();
```

## Connect to a database of a secondary app

If you want to address a database from a different Firebase project, you will need to create a secondary app first
(Read more on creating a secondary app here: https://rnfirebase.io/app/usage).
For example:

```js
import database, { firebase } from '@react-native-firebase/database';

// create a secondary app
const secondaryApp = await firebase.initalizeApp(credentials, config);

// pass the secondary app instance to the database module
const secondaryDatabase = database(secondaryApp);

secondaryDatabase.ref();
```

# firebase.json

## Disabling persistence

By default the Realtime Database persists data on the user application, and is used by the SDKs for offline usage
and caching. To disable this functionality, update the `database_persistence_enabled` key in the `firebase.json` file:

```json
// <project-root>/firebase.json
{
  "react-native": {
    "database_persistence_enabled": false
  }
}
```

To enable persistence, view the [Offline Support](/database/offline-support) documentation.