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 Map

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

Custom Class

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

Retrieving a collection of objects with relations¶

DataQueryBuilder queryBuilder = DataQueryBuilder();
queryBuilder.related = ["RELATED-PROPERTY-NAME", 
                        "RELATED-PROPERTY-NAME.RELATION-OF-RELATION-PROP-NAME"];

Then load data using the constructed queryBuilder object with:

Using Map

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

Custom Class

Future<List<E>> Backendless.data.withClass<E>().find([DataQueryBuilder queryBuilder]);

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.
`E`	Reference to a class which identifies the table from which the data should be loaded from.

Important

There are some limitations for the related object retrieval. Since Dart cannot reflect the type of the list in the runtime, there are two ways to declare the collection of related objects inside the custom parent class:

@reflector
class ParentTable {
  List<dynamic> children;  
}

or

@reflector
class ParentTable {
  List<ChildTable> _children;  
  set children(List value) => _children = value.cast<ChildTable>();  
  get children => _children;
}