Q:

JPA mapping for inserting a relationship

I am using JPA to persist my entities. Suppose I have a ManyToMany relationship between the entity A and B. So, in the class A it will be a List<B> and in B a List<A>. 
My question is about the efficiency of adding a new relationship. 
In the easy way I can make a add(new B()) in the list in class A. Will this List of B objects in the class A will all be loaded from the database when I call the add method in runtime? Is this efficient? 
If I have 200 relationships, it will load all of them, to simply add a new object B? It will be better to create a native query to insert a new row the ManyToMany table.

A:

The behavior of add() on a List is dependent on the JPA provider.
For EclipseLink, for a LAZY List relationship add() will not cause the list to be fetched by default.

