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.

Method¶

Using Map

Future<int> Backendless.data.of("TABLE-NAME").setRelation(
                 String parentObjectId, 
                 String relationColumnName, 
                {List<String> childrenObjectIds, 
                 String whereClause});

Custom Class

Future<int> Backendless.data.withClass<E>().setRelation(
                  String parentObjectId, 
                  String relationColumnName, 
                 {List<String> childrenObjectIds, 
                  String whereClause});

where:

Argument	Description
`TABLE-NAME`	name of the table where the parent object is stored.
`E`	Dart class of the parent object. The class name identifies the table where the parent object is stored.
`parentObjectId`	the ID of an object which will be assigned related children for `relatedColumnName`. When this argument is an instance of `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
`childrenObjectIds`	a collection of child object IDs to set into the relation identified by `relatedColumnName.` For the one-to-one relations the collection must contain one element.

Return Value¶

Number of child objects set into the relation.

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 Map

Map parentObject = // parentObject retrieval is out of scope in this example
Map childObject = // childObject retrieval is out of scope in this example

Backendless.data.of("Person").setRelation(parentObject['objectId'], "address", 
  children: [childObject['objectId']]).then((response) {
    // relation has been set
});

Custom Class

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

Backendless.data.withClass<Person>().setRelation(personObject.objectId, "address", 
  children: [addressObject.objectId]).then((response) {
    // relation has been set
});