Conditional Delivery of New Objects

Consider the following data table. The table name is Order and it contains the orderAmount column which will be used in the example:

The code below adds a listener for the create event for the Order table.

Using DictionaryCustom Class

var orderEventHandler = Backendless.Data.Of( "Order" ).RT();

orderEventHandler.AddCreateListener( "orderAmount > 1000", createdOrder =>
{
    Console.WriteLine( $"new Order object has been created. Object ID - {createdOrder["objectId"]}");
} );

Assume the following class represents objects from the Order table:

public class Order
{
  public string ObjectId{ get; set; }
  public string OrderName{ get; set; }
  public double OrderAmount{ get; set; }
}

Then the following code will create an event listener for any new orders where OrderAmount is greater than 1000:

var orderEventHandler = Backendless.Data.Of<Order>().RT();

orderEventHandler.AddCreateListener( "OrderAmount > 1000", createdOrder =>
{
    Console.WriteLine( $"new Order object has been created. Object ID - {createdOrder.ObjectId}");
} );

The event listener will receive only the Order objects where the amount of order is greater than 1000. This is achieved with the first argument in the AddCreateListener method. The argument is a where clause condition, which references the orderAmount column and requests that the real-time database sends only the matching objects. The second argument is a callback object which will receive any new object which matches the where clause condition. Notice the argument of the delegate function method is the actual object saved in the database.

For more information about the whereClause syntax, see the Condition Syntax section of the guide.