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¶

Using Java MapCustom Class

Synchronous methods:

public Map Backendless.Data.of( "TABLE-NAME" ).findFirst( int relationsDepth );
public Map Backendless.Data.of( "TABLE-NAME" ).findLast( int relationsDepth );
public Map Backendless.Data.of( "TABLE-NAME" ).findById( String objectId, int relationsDepth );
public List<Map> Backendless.Data.of( "TABLE-NAME" ).find( DataQueryBuilder queryBuilder );

Asynchronous methods:

public void Backendless.Data.of( "TABLE-NAME" ).findFirst( int relationsDepth,
                                                      AsyncCallback<Map> responder  );
public void Backendless.Data.of( "TABLE-NAME" ).findLast( int relationsDepth, 
                                                      AsyncCallback<Map> responder  );
public void Backendless.Data.of( "TABLE-NAME" ).findById( String objectId, int relationsDepth, 
                                                      AsyncCallback<Map> responder  );
public void Backendless.Data.of( "TABLE-NAME" ).find( DataQueryBuilder dataQuery, 
                                                      AsyncCallback<List<Map>> responder );

Synchronous methods:

public T Backendless.Data.of( T.class ).findFirst( int relationsDepth );
public T Backendless.Data.of( T.class ).findLast( int relationsDepth );
public T Backendless.Data.of( T.class ).findById( String objectId, int relationsDepth );
public List<T> Backendless.Data.of( T.class ).find( DataQueryBuilder queryBuilder );

Asynchronous methods:

public void Backendless.Data.of( T.class ).findFirst( int relationsDepth,
                                                      AsyncCallback<E> responder  );
public void Backendless.Data.of( T.class ).findLast( int relationsDepth, 
                                                      AsyncCallback<E> responder  );
public void Backendless.Data.of( T.class ).findById( String objectId, int relationsDepth, 
                                                      AsyncCallback<E> responder  );
public void Backendless.Data.of( T.class ).find( DataQueryBuilder queryBuilder, 
                                                      AsyncCallback<List<T>> responder );

Example¶

Using Java MapCustom Class

DataQueryBuilder queryBuilder = DataQueryBuilder.create();
queryBuilder.setRelationsDepth( 2 );

// synchronous call
List<Map> collection = Backendless.Data.of( "Foo" ).find( queryBuilder );

// asynchronous call
Backendless.Data.of( "Foo" ).find( queryBuilder, 
                            new AsyncCallback<List<Map>>()
    {
      @Override
      public void handleResponse( List<Map> response )
      {

      }

      @Override
      public void handleFault( BackendlessFault fault )
      {

      }
    });

DataQueryBuilder queryBuilder = DataQueryBuilder.create();
queryBuilder.setRelationsDepth( 2 );

// synchronous call
List<Foo> collection = Backendless.Data.of( Foo.class ).find( queryBuilder );

// asynchronous call
Backendless.Data.of( Foo.class ).find( queryBuilder, 
                   new AsyncCallback<List<Foo>>()
{
  @Override
  public void handleResponse( List<Foo> response )
  {

  }

  @Override
  public void handleFault( BackendlessFault fault )
  {

  }
});