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ObjectBox Examples

If you want to dive straight into the code:

Data model

In the following file, e.g. models.dart, we import ObjectBox to access annotations. Then, we define a single "Entity" that should be persisted by ObjectBox. You can have multiple entities in the same file, or you can have them spread across multiple files in your package's lib directory.

import 'package:objectbox/objectbox.dart';

@Entity()
class Note {
    // Each "Entity" needs a unique integer ID property.
    // Add `@Id()` annotation if its name isn't "id" (case insensitive).
    int id;

    String text;

    int date;

    @Transient() // Make this field ignored, not stored in the database.
    int notPersisted;

    // An empty default constructor is needed but you can use optional args.
    Note({this.text});

    // Note: just for logs in the examples below(), not needed by ObjectBox.
    toString() => 'Note{id: $id, text: $text}';
}

To generate ObjectBox binding code for your entities, run pub run build_runner build. ObjectBox generator will look for all @Entity annotations in your lib folder and create a single database definition lib/objectbox-model.json and supporting code in lib/objectbox.g.dart. You should commit objectbox-model.json into your source control (e.g. git) and add objectbox.g.dart to the ignore list (e.g. .gitignore), otherwise the build_runner will complain about it being changed each time you pull a change.

The generator will process lib and test folders separately and create a separate database in each one, if it finds annotations there. This is useful if you need a separate test DB. If you're just writing tests for your own code, you won't have any annotations in the test folder so no DB will be created there.

Creating a store

Store is your entrypoint to ObjectBox - see below how to open it, based on the SDK you're using.

Flutter apps

On mobile devices, you should store data in your app documents directory - it stays there even when you close the app.

Use getApplicationDocumentsDirectory() from the path_provider package to retrieve this directory.

import 'package:path_provider/path_provider.dart';

import 'objectbox.g.dart'; // created by `flutter pub run build_runner build`

class _MyHomePageState extends State<MyHomePage> {
  Store _store;

  @override
  void initState() {
    super.initState();

    getApplicationDocumentsDirectory().then((Directory dir) {
      // Note: getObjectBoxModel() is generated for you in objectbox.g.dart
      _store = Store(getObjectBoxModel(), directory: dir.path + '/objectbox');
    });
  }

  @override
  void dispose() {
    _store?.close();  // don't forget to close the store
    super.dispose();
  }
}

See Flutter: read & write files for more info. If you didn't specify this path to ObjectBox, it would try to use a default directory "objectbox" in the current working directory, but it doesn't have permissions to write there: failed to create store: 10199 Dir does not exist: objectbox (30).

Dart CLI apps

In standard apps (not on mobile), ObjectBox can write anywhere the current user can. The following minimal example omits the argument to Store(directory: ), thus using the default - 'objectbox' in the current working directory.

import 'objectbox.g.dart'; // created by `dart pub run build_runner build`

void main() {
  var store = Store(getObjectBoxModel()); // Note: getObjectBoxModel() is generated for you in objectbox.g.dart

  // your app code ...

  store.close(); // don't forget to close the store
}

Box

Box<Entity> is your main interface for storing and retrieving data. Objects are stored using box.put() which checks the ID and:

  • assigns a new object a unique non-zero ID - new objects are those that have a zero or null ID,
  • or if the object already has an ID, overwrites an object with that ID.
import 'objectbox.g.dart';

final box = store.box<Note>();

final note = Note(text: 'Hello'); // note: node.id is null
final id = box.put(note);         // note: sets note.id and also returns it
print('new note got id=${id}, which is the same as note.id=${note.id}');
print('refetched note: ${box.get(id)}');

Queries

The generated objectbox.g.dart contains a "meta-information" class for your entity, called Note_ in our example. This class contains all fields in your entity, with the information necessary to create queries in a type-safe manner.

box.putMany([Note(), Note(), Note(), Note(text: 'Hello world!')]);

final queryNullText = box.query(Note_.text.isNull()).build();

assert(queryNullText.count() == 3);             // executes the query, returns int
final notesWithNullText = queryNullText.find(); // executes the query, returns List<Note>

queryNullText.close(); // close the query to free resources

More complex queries can be constructed using and/or operators. Also there is basic operator overloading support for greaterThan, lessThan, and and or, respectively >, <, &, |.

box.query(Note_.text.isNull().or(Note_.date.greaterThan())).build();

// equivalent to

box.query(Note_.text.isNull() | Note_.date > 0).build();

Ordering query results

The results from a query can be ordered using the order method, e.g.

final q = box.query(Note_.date > 0)
  .order(Note_.date)
  .build();

// ...

final qt = box.query(Note_.text.notNull())
  .order(Note_.text, flags: Order.descending | Order.caseSensitive)
  .build();

Property Queries

Use "Property Queries" If you're interested only in a single property from an Entity. You can access a list of property values across matching objects, or an aggregation.

final query = box.query(Note_.date > 0).build()

// Use distinct or caseSensitive to refine results.
final textQuery = query.stringProperty(Note_.text)
    ..distinct = true
    ..caseSensitive = true;
final texts = textQuery.find();
textQuery.close();

// Get aggregates, like min, max, avg, sum and count.
final dateQuery = query.integerProperty(Note_.date);
final min = dateQuery.min();
dateQuery.close();

// You can also change how stored `null` values are handled, use [replaceNullWith].
final dateQuery = query.integerProperty(Note_.score);
final dates = scoreQuery.find(replaceNullWith: 0);
dateQuery.close();

query.close();

Query streams

Streams can be created from queries. Note: Dart Streams can be extended with rxdart.

final query = box.query(condition).build();
final queryStream = query.stream;
final sub1 = queryStream.listen((query) {
  print(query.count());
});

// box.put() creates some data ...

sub1.cancel();

final stream = query.findStream(limit:5);
final sub2 = stream.listen((list) {
  // ...
});

// clean up
sub2.cancel();

Relations

Objects may reference other objects, for example using a simple reference or a list of objects. In database terms, we call those references relations. The object defining the relation we call the source object, the referenced object we call target object. So the relation has a direction.

If there is one target object, we call the relation to-one. And if there can be multiple target objects, we call it to-many. Relations are lazily initialized: the actual target objects are fetched from the database when they are first accessed. Once the target objects are fetched, they are cached for further accesses.

You define a to-one relation using the ToOne class, a smart proxy to the target object. It gets and caches the target object transparently. For example, an order is typically made by one customer. Thus, we could model the Order class to have a to-one relation to the Customer.

Similarly, you can define a to-many relation using the ToMany class, which you can use as an ordinary list in your code and it takes care of loading/storing the relational data for you.

Have a look at the following example how a shop database could look like.

@Entity()
class Customer {
  int id;
  String name;
}

@Entity()
class Order {
  int id;

  final customer = ToOne<Customer>();
  final items = ToMany<Item>();
}

@Entity()
class Item {
  int id;
}

Now, let’s say a new customer has just confirmed an order through the UI. We need to create the Customer and the Order in the database, attaching a list of purchased items. We assume those items are already stored in the DB, customer must heve selected them somehow, right?

List<Item> purchasedItems = [...]; // loaded from the shopping basket

// create a new order with a new customer
final order = Order();
order.customer.target = Customer()..name="John Doe"; // add a new Customer object
order.items.addAll(purchasedItems); // add a list of existing items

// create the order and the customer in the database with a single call
store.box<Order>().put(order);

Backlink to a ToOne relation

For every ToOne relation that you have, you can define a backlink. Backlinks are using the same relation information, but in the reverse direction. Thus, a backlink of a ToOne will result in a list of potentially multiple objects: all objects pointing to the same target.

Example: Two Order objects point to the same Customer using a ToOne. The backlink is a ToMany from the Customer referencing its two Order objects. The updated schema from the previous example could look like this:

@Entity()
class Customer {
  int id;
  String name;
  
  @Backlink()
  final orders = ToMany<Order>();
}

@Entity()
class Order {
  int id;

  final customer = ToOne<Customer>();
  final items = ToMany<Item>();
}

@Entity()
class Item {
  int id;
}

Note: if you change the customer.orders list, you're actually changing order.customer.targetId on each target.

Backlink to a ToMany relation

Similarly to "backlinking" a ToOne relation, you can add a backlink against another ToMany relation, creating a view of its data for an easy access from the target object. Again, let's update the previous example schema, adding a such a backlink to Item, so that we can access all Orders where this Item was sold.

@Entity()
class Customer {
  int id;
  String name;
}

@Entity()
class Order {
  int id;

  final customer = ToOne<Customer>();
  final items = ToMany<Item>();
}

@Entity()
class Item {
  int id;
  
  @Backlink()
  final orders = ToMany<Order>();
}