Two Steps Retrieval¶
Important
Two Step Retrieval loads 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.
With this approach a collection of related objects for a specific relation property in a parent object is retrieved from the server. The client application must know parent object's objectId
. The API loads a collection of related children for one property at a time. Child objects retrieved in paged sets, see the Relation Paging API sectionfor additional details.
Suppose the Person
table has a one-to-many relationship column friends
pointing to the Users
table. The code below retrieves related BackendlessUser
objects for a specific Person
object:
¶
Prepare LoadRelationsQueryBuilder:
LoadRelationsQueryBuilder<Map> loadRelationsQueryBuilder; loadRelationsQueryBuilder = LoadRelationsQueryBuilder.ofMap("friends");
String parentObjectId = // removed for brevity Backendless.data.of("Person").loadRelations(parentObjectId, loadRelationsQueryBuilder).then((friends) { for (Map friend in friends) { print(friend['email']); } });
Prepare LoadRelationsQueryBuilder:
LoadRelationsQueryBuilder<Person> loadRelationsQueryBuilder; loadRelationsQueryBuilder = LoadRelationsQueryBuilder.of<Person>("friends");
String parentObjectId = // removed for brevity Backendless.data.withClass<Person>().loadRelations(parentObjectId, loadRelationsQueryBuilder).then((friends) { for (Person friend in friends) { print(friend.email); } });