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Set/Add Relation with objects

API request must identify the child objects to set/add to the relation explicitly by referencing their IDs.

Methods

Set relation - POST

Add relation - PUT

URL

https://api.backendless.com/<application-id>/<REST-api-key>/data/<table-name>/<parentObjectId>/<relationName> 

where:

Argument                Description
<application-id> the ID of your application generated upon its creation. You can obtain the value in the Manage > App Settings section of the Backendless Console.
<REST-api-key> REST API key of your application. You can obtain the value in the Manage > App Settings section of the Backendless Console.
<table-name> name of the table where which contains the parent object as identified by <parentObjectId>.
<parentObjectId> id of the object for which the relation will be created/set.
<relationName> name of the column which identifies the relation within the parent table (identified as <table-name>). 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.

Request Headers

user-token: value-of-the-user-token-header-from-login  
Content-Type:application/json

where:

Argument                Description
user-token Optional header. Contains a value returned by Backendless in a preceding user Login API call. If user-token is set in the request, the operation will be executed with the security policy associated with the currently logged in user. This means all permissions associated with the user and the roles assigned to the user will be enforced by Backendless.
Content-Type Must be set to application/json. This header is mandatory.

Request Body

Must be an array of child object IDs as string values.

[  
  "childObjectId1", "childObjectId2"  
]

Return Value

Error or number of objects the operation sets for 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 URL - notice the relation column is address. If it were specified as address:Address:1, then the column would be created automatically.
relation-column

curl request:

curl \  
-H Content-Type:application/json \  
-X POST  
-d "{ \"XXXXX-XXXXX-XXXXX-XXXXX\" }" \  
https://api.backendless.com/application-id/REST-api-key/data/Person/parentObjectId/address


The following example sets a relation for a one-to-many column named friends which will be created if missing in the Person table. The column points to the Users table:

curl \  
-H Content-Type:application/json \  
-X POST  
-d "{ \"XXXXX-XXXXX-XXXXX-XXXXX\" }" \  
https://api.backendless.com/application-id/REST-api-key/data/Person/parentObjectId/friends:Users:n

Since the path includes the name of the child table (see the part of the path which included friends:Users:n), Backendless will create the column if it does not exist. Once created, you can see the column in Backendless console:
friends-column-created