Unconditional Delivery Listeners

The where clause argument in the addUpdateListener method is optional. When it is not provided, the real-time database will deliver any object  which is being updated in the database's table:

Using Untyped ObjectsCustom Class/Function

const orderEventHandler = Backendless.Data.of('Order').rt();

const onObjectUpdate = object => 
                       console.log( 'an Order object has been updated. Object ID - ', object.objectId );

const onError = error => 
                console.log( 'An error has occurred -', error );

orderEventHandler.addUpdateListener( onObjectUpdate, onError );

function Order() {
  this.objectId = undefined;
  this.orderAmount = 0;
}

const orderEventHandler = Backendless.Data.of( Order ).rt();

const onObjectUpdate = object => 
                       console.log( 'an Order object has been updated. Object ID - ', object.objectId );

const onError = error => 
                console.log( 'An error has occurred -', error );

orderEventHandler.addUpdateListener( onObjectUpdate, onError );

Codeless Reference

where:

Argument	Description
id	Unique identifier of the new event listener.
table name	The name of the data table where a conditional event listener must be registered.
where clause	Optional parameter. Sets the condition for an event listener which gets triggered every time the condition is met when the update operation is invoked for a specific data table. For more information about the where clause syntax, see the Condition Syntax section of the guide.
object	When a listener gets triggered, the Backendless delivers a callback object containing the updated object to the listener.

The example below registers a new event listener for the "Person" data table with the id``"1EFD-3GEF2-FF4C-AC21". The listener is triggered when an existing object is updated in the data table.

Assume an object in the data table is updated, and the Codeless logic below executes a custom block of code; First the following sentence is printed: "Update operation has triggered the listener.", then the value of the property objectId is retrieved from the object variable and also gets printed.