Set Relation with objects¶

API request replaces related objects with the ones identified in the API call. Child objects must be explicitly defined by referencing their IDs.

Blocking API¶

Using Java Map

Integer result = Backendless.Persistence.of( "TABLE-NAME" ).setRelation( 
                                                   Map parentObject,
                                                   String relationColumnName,
                                                   Collection<Map> children );

Custom Class

Integer result = Backendless.Persistence.of( E ).setRelation( 
                                                   E parentObject,
                                                   String relationColumnName,
                                                   Collection<T> children );

Non-Blocking API¶

Using Java Map

Backendless.Persistence.of( "TABLE-NAME" ).setRelation( 
                                             Map parentObject,
                                             String relationColumnName,
                                             Collection<Map> children,
                                             AsyncCallback<Integer> callback );

Custom Class

Backendless.Persistence.of( E ).setRelation( 
                                   E parentObject,
                                   String relationColumnName,
                                   Collection<T> children,
                                   AsyncCallback;<Integer> callback );

where:

Argument	Description
`TABLE-NAME`	name of the table where the parent object is stored.
`E`	Java class of the parent object. The class name identifies the table where the parent object is stored.
`parentObject`	the object which will be assigned related children for `relatedColumnName`. When this argument is an instance of `java.util.Map` (for the map-based approach), it must contain the `"objectId"` property.
`relationColumnName`	name of the column identifying the relation. Objects from the `children` collection will be set as related for the column in `parentObject`. The column name may optionally include table name separated by the colon character as well as cardinality which determines the type of relationship (one to one or one to many) (see the note below):

Important

If the column does not exist in the parent table at the time when the API is called, the value of the "relationColumnName" argument must include the name of the child table separated by colon and the cardinality notation. The cardinality is expressed as ":1" for one-to-one relations and ":n" for one-to-many relations. For example, the value of "myOrder:Order:1" will create a one-to-one relation column "myOrder" in the parent table. The column will point to the Order child table. Likewise, the value of "myOrder:Order:n" will create a one-to-many relation column "myOrder" pointing to the Order table.

Argument	Description
`children`	a collection of child objects to set into the relation identified by `relatedColumnName.` For the one-to-one relations the collection must contain one element.
`callback`	a responder object which will receive a callback when the relation has been set or if an error occurs. Applies to the asynchronous method only.

Return Value¶

Number of child objects set into the relation. The asynchronous call receives the return value through a callback executed on the AsyncCallback object.

Example¶

The example below sets a relation for a one-to-one column named address declared in the Person table. The column must be declared in the table prior to the execution of the request shown below. This necessity is explained by missing table name qualifier in the relationColumnName argument - notice the relation column is "address". If the argument value were "address:Address:1", then the column would be created automatically.
relation-column

Using Java Map

HashMap<String, Object> parentObject = new HashMap<String, Object>();
parentObject.put( "objectId", "41230622-DC4D-204F-FF5A-F893A0324800" );

HashMap<String, Object> childObject = new HashMap<String, Object>();
childObject.put( "objectId", "3464C734-F5B8-09F1-FFD3-18647D12E700" );

ArrayList<Map> children = new ArrayList<Map>();
children.add( childObject );

Backendless.Data.of( "Person" ).setRelation( parentObject, "address", children, 
                                             new AsyncCallback<Integer>()
{
  @Override
  public void handleResponse( Integer response )
  {
    Log.i( "MYAPP", "relation has been set" );
  }

  @Override
  public void handleFault( BackendlessFault fault )
  {
    Log.e( "MYAPP", "server reported an error - " + fault.getMessage() );
  }
} );

Custom Class

Person personObject = // personObject retrieval is out of scope in this example
Address addressObject = // addressObject retrieval is out of scope in this example

ArrayList<Address> addressCollection = new ArrayList<Address>();
addressCollection.add( addressObject );

Backendless.Data.of( Person.class ).setRelation( personObject, "address", addressCollection,
        new AsyncCallback<Integer>()
        {
          @Override
          public void handleResponse( Integer response )
          {
            Log.i( "MYAPP", "relation has been set");
          }

          @Override
          public void handleFault( BackendlessFault fault )
          {
            Log.e( "MYAPP", "server reported an error - " + fault.getMessage() );
          }
        } );