Single Step Retrieval¶

Important

Single 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 .

This approach allows retrieval of a partial set of the related objects along with the parent object in a single findor findById request. Each relationship property (column) must be uniquely identified by name using the API documented below.

Retrieving a specific object with relations¶

Using Java MapCustom Class

Non-blocking call:

Backendless.Data.of( "TABLE-NAME" ).findById( 
                  String objectId, 
                  List<String> relations,
                  AsyncCallback<Map<String, Object>> responder )

Blocking call:

Map<String, Object> result = Backendless.Data.of( "TABLE-NAME" ).findById( 
                  String objectId, 
                  List<String> relations )

Non-blocking call:

Backendless.Data.of( T.class ).findById( 
                  String objectId, 
                  List<String> relations,
                  AsyncCallback<T> responder )

Blocking call:

T result = Backendless.Data.of( T.class ).findById( 
                  String objectId, 
                  List<String> relations )

Retrieving a collection of objects with relations¶

DataQueryBuilder queryBuilder = DataQueryBuilder.create();
queryBuilder.addRelated( "RELATED-PROPERTY-NAME" )
queryBuilder.addRelated( "RELATED-PROPERTY-NAME.RELATION-OF-RELATION-PROP-NAME" );

// alternatively, you can use the addRelated method, which 
// accepts a collection of related column names:
List<String> relations = new ArrayList<String>();
relations.add( "RELATED-PROPERTY-NAME" );
relations.add( "RELATED-PROPERTY-NAME.RELATION-OF-RELATION-PROP-NAME" );
queryBuilder.addRelated( relations );

Then load data using the constructed queryBuilder object with:

Using Java MapCustom Class

Synchronous call:

List<Map> collection = Backendless.Data.of( "TABLE-NAME" ).find( queryBuilder );

Asynchronous call:

Backendless.Data.of( "TABLE-NAME" ).find( queryBuilder, AsyncCallback<List<Map>> callback );

Synchronous call:

List<T> collection = Backendless.Data.of( T.class ).find( queryBuilder );

Asynchronous call:

Backendless.Data.of( T.class ).find( queryBuilder, AsyncCallback<List<T>> callback );

where

Argument	Description
`RELATED-PROPERTY-NAME`	name of a related property to load. For example, if table `Person` has a relation "`homeAddress`" pointing to an object in the `Address` table, the value would be "`homeAddress`". The syntax allows to add relations of relations. For example, if the same `Address` table has a relation "`country`" pointing to the `Country` table, then "`homeAddress.country`" would instruct the related `Country` object to be loaded as well.
`queryBuilder`	an instance of the `com.backendless.persistence.DataQueryBuilder` class. The class is used to identify related properties for relation retrieval, paging, sorting and search with whereClause.
`TABLE-NAME`	Name of the table where the data should be retrieved from.
`T.class`	Reference to a class which identifies the table from which the data should be loaded from.