JSON POST to create class with many to many set to second class

I have two classes A and B, class A has a Many to Many (field set) to class B. When I generate the web mvc web interface this allows a multiple select from existing objects of type B to get added on the create of class A.

When I use JSON each create of A, causes creates for type B for whichever are included is there additionally a way to have JSON behave like the web interface and refer to existing objects of type B?

This exists in the pizzashop example for toppings (type B) to pizzas (type A)