Quick Start - Flutter SDK

Create Data Model

To define your application's data model, add a Realm model class definition to your application code.

Some considerations when defining your Realm model class:

• Import package at the top of your class definition file.

• In your file, give your class a private name (starting with _), such as a file car.dart with a class _Car. You generate the public RealmObject class using the command in the following Generate RealmObject Class section. This command outputs a public class, such as Car.

• Make sure to include the generated file name, such as part car.realm.dart, before the code defining your model. This is required to generate the RealmObject class.

import 'package:realm/realm.dart';
part 'car.realm.dart';
@RealmModel()
class _Car {
  @PrimaryKey()
  late ObjectId id;
  late String make;
  late String? model;
  late int? miles;
}

import 'package:realm_dart/realm.dart';
part 'car.realm.dart';
@RealmModel()
class _Car {
  @PrimaryKey()
  late ObjectId id;
  late String make;
  late String? model;
  late int? miles;
}

Generate RealmObject Class

Now generate a RealmObject class Car from the data model class Car:

dart run realm generate

dart run realm_dart generate

Running this creates a Car class in a car.realm.dart file located in the directory where you defined the model class per the preceding Create Data Model section. This Car class is public and part of the same library as the _Car data model class. The generated Car class is what's used throughout your application.

If you'd like to watch your data model class to generate a new Car class whenever there's a change to _Car, run:

dart run realm generate --watch

dart run realm_dart generate --watch

Create Objects

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

final car = Car(ObjectId(), 'Tesla', model: 'Model S', miles: 42);
realm.write(() {
  realm.add(car);
});

Update Objects

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

realm.write(() {
  car.miles = 99;
});

Query for Objects

Retrieve a collection of all objects of a data model in the realm with the Realm.all() method:

final cars = realm.all<Car>();
final myCar = cars[0];
print('My car is ${myCar.make} ${myCar.model}');

Filter a collection to retrieve a specific segment of objects with the Realm.query() method. In the query() method's argument, use Realm Query Language operators to perform filtering.

final cars = realm.query<Car>('make == "Tesla"');

Delete Objects

Delete a car by calling the Realm.delete() method in a write transaction block:

realm.write(() {
  realm.delete(car);
});

React to Changes

Listen and respond to changes to a query, a single object, or a list within an object. The change listener is a Stream that invokes a callback function with an containing changes since last invocation as its argument.

To listen to a query, use RealmResults.changes.listen().

// Listen for changes on whole collection
final characters = realm.all<Character>();
final subscription = characters.changes.listen((changes) {
  changes.inserted; // Indexes of inserted objects.
  changes.modified; // Indexes of modified objects.
  changes.deleted; // Indexes of deleted objects.
  changes.newModified; // Indexes of modified objects after accounting for deletions & insertions.
  changes.moved; // Indexes of moved objects.
  changes.results; // The full List of objects.
  changes.isCleared; // `true` after call to characters.clear(); otherwise, `false`.
});
// Listen for changes on RealmResults.
final hobbits = fellowshipOfTheRing.members.query('species == "Hobbit"');
final hobbitsSubscription = hobbits.changes.listen((changes) {
  // ... all the same data as above
});

You can pause and resume subscriptions as well.

subscription.pause();
// The changes.listen() method won't fire until subscription is resumed.
subscription.resume();

Once you've finished listening to changes, close the change listener to prevent memory leaks.

await subscription.cancel();

For more information, refer to React to Changes.

Prerequisites

Before you can use Device Sync with Realm in your client app, you must configure Device Sync using Atlas App Services:

1. Create an App Services App

2. Enable Anonymous Authentication

3. Enable Flexible Sync. Set owner_id as a queryable field.

4. Define the rules that determine which permissions users have when using Device Sync. For this example, we assign a default role, which applies to any collection that does not have a collection-specific role. In this example, a user can read and write data where the user.id of the logged-in user matches the owner_id of the object:

   {
     "roles": [
       {
         "name": "owner-read-write",
         "apply_when": {},
         "document_filters": {
           "write": {
             "owner_id": "%%user.id"
           },
           "read": {
             "owner_id": "%%user.id"
           }
         },
         "read": true,
         "write": true,
         "insert": true,
         "delete": true,
         "search": true
       }
     ]
   }

Now, deploy your application updates.

Initialize App Services

To use App Services features such as authentication and sync, access your App Services App using your App ID. You can find your App ID in the App Services UI.

final app = App(AppConfiguration(APP_ID));

For more information, refer to Connect to App Services.

Authenticate a User

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

final loggedInUser = await app.logIn(Credentials.anonymous());

For more information, refer to Authenticate a User.

Open a Synced Realm

Once you have enabled Device Sync and authenticated a user, open a synced realm with Configuration.flexibleSync(). Then, pass the configuration to Realm() to open an instance of the realm. The synced realm must have a different Configuration.path from other opened local-only realms.

final config = Configuration.flexibleSync(loggedInUser, [Todo.schema]);
final realm = Realm(
  config,
);

For more information, refer to Open a Synced Realm.

Add a Sync Subscription

Now create a subscription to synchronize data with Atlas using Device Sync. Add the subscription within the SubscriptionSet.update() callback function.

The update block callback function, includes a MutableSubscriptionSet() object as an argument. Use MutableSubscriptionSet.add() to add a new subscription.

// Check if the subscription already exists before adding
final userTodoSub = realm.subscriptions.findByName('getUserTodos');
if (userTodoSub == null) {
  realm.subscriptions.update((mutableSubscriptions) {
    // server-side rules ensure user only downloads their own Todos
    mutableSubscriptions.add(realm.all<Todo>(), name: 'getUserTodos');
  });
}

For more information, refer to Manage Sync Subscriptions.