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Retrieval with Relation Depth

The Data Service API supports a mechanism for loading related objects without identifying each by its name. Instead, the API includes a parameter which specifies the "depth" of the relations to include into the response. Consider the following diagram:

relation-depth

The diagram shows a hierarchy for class structure - the Order class has two relations: with OrderItem and Customer classes. Each in turn has a relation to the Manufacturer and Address classes. When an instance or a collection of Order objects is retrieved from Backendless, the API may include a parameter specifying the depth of relations to include into the response. If the relation depth is 1, then all related instances of OrderItem and Customer will be included into each Order object. If the relation depth is 2, then not only OrderItem and Customer instances will be included, but the corresponding Manufacturer and Address objects as well.

Important

Loading relations with relation depth retrieves only a partial set of the related objects (default size of the retrieved related collection is 10). To load additional related objects, use the Relation Paging API.

API methods supporting relations depth

Future<List<Map>> Backendless.data.of("TABLE-NAME").find([DataQueryBuilder queryBuilder]);

Future<Map> Backendless.data.of("TABLE-NAME").findFirst({List<String> relations, int relationsDepth});

Future<Map> Backendless.data.of("TABLE-NAME").findLast({List<String> relations, int relationsDepth});

Future<Map> Backendless.data.of("TABLE-NAME").findById(
      String id,
     {List<String> relations,
      int relationsDepth,
      DataQueryBuilder queryBuilder});
Future<List<E>> Backendless.data.withClass<E>().find([DataQueryBuilder queryBuilder]);

Future<E> Backendless.data.withClass<E>().findFirst({List<String> relations, int relationsDepth});

Future<E> Backendless.data.withClass<E>().findLast({List<String> relations, int relationsDepth});

Future<E> Backendless.data.withClass<E>().findById(String id,
    {List<String> relations,
    int relationsDepth,
    DataQueryBuilder queryBuilder});

Example

DataQueryBuilder queryBuilder = DataQueryBuilder()
  ..relationsDepth = 2;
Backendless.data.of("Foo").find(queryBuilder).then((response) {
  print("Found objects: $response");
});
DataQueryBuilder queryBuilder = DataQueryBuilder()
  ..relationsDepth = 2;
Backendless.data.withClass<Foo>().find(queryBuilder).then((response) {
  print("Found objects: $response");
});