Quick Start with Sync - Java SDK

Initialize Realm

Before you can use Realm in your app, you must initialize the Realm library. Your application should initialize Realm just once each time the application runs.

To initialize the Realm library, provide an Android context to the Realm.init() static function. You can provide an Activity, Fragment, or Application context for initialization with no difference in behavior. You can initialize the Realm library in the onCreate() method of an application subclass to ensure that you only initialize Realm once each time the application runs.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="com.mongodb.example">
   <application
      android:name=".MyApplicationSubclass"
      ...
   />
</manifest>

Initialize the App

To use MongoDB Realm features such as authentication and sync, you must access your Realm app using your Realm app ID. You can find your Realm app ID in the Realm UI.

Define Your Object Model

Your application's data model defines the structure of data stored within Realm Database and synchronized to and from MongoDB Realm. You can define your application's data model in two ways:

• Via schemas in MongoDB Realm.
• Via Kotlin or Java classes in your application code with Realm Object Models.

This quick start uses the latter approach, which defines your schema using classes in your mobile application code. To define your Realm app's object model in this way, you need to enable Development Mode.

Once you've enabled Development Mode, add the following class definitions to your application code:

Authenticate a User

When you have enabled anonymous authentication in the Realm UI, users can immediately log into your app without providing any identifying information:

Realm provides many additional ways to authenticate, register, and link users.

Open a Realm

Once you have enabled Realm Sync and authenticated a user, you can open a synced realm. Use the SyncConfiguration to control the specifics of how your application synchronizes data with MongoDB Realm, including the partition, how long to wait before a request times out, whether to allow synchronous reads or writes to a realm on the UI thread, and more.

Create, Read, Update, and Delete Objects

Once you have opened a realm, you can modify the objects within that realm in a write transaction block.

To create a new Task, instantiate an instance of the Task class and add it to the realm in a write block:

You can retrieve a live collection of all items in the realm:

You can also filter that collection using a filter:

To modify a task, update its properties in a write transaction block:

Finally, you can delete a task by calling the deleteFromRealm() method in a write transaction block:

Watch for Changes

You can watch a realm, collection, or object for changes by attaching a custom OrderedRealmCollectionChangeListener with the addChangeListener() method:

Log Out

Once logged in, you can log out:

Complete Example

Run the complete example by replacing the appId with your realm app ID. If you're running this project in a fresh Android Studio project, you can copy and paste this file into your application's MainActivity -- just remember to:

• change the package declaration so it matches your project
• replace the App ID placeholder with your Realm app's App ID
• update the import statements for Task and TaskStatus if you're using java

Output

Running the above code should produce output resembling the following:

Successfully authenticated anonymously.
Updated range: 0 to 1
Deleted range: 0 to 1
Successfully logged out.