How to use @BasicMap for a HashMap whose key values are entities

How should I use EclipseLink's @BasicMap annotation for a map whose key value is an entity and the value is an Integer?

@Entity
class A {

   // This doesn't work, as the key is an entity
   @BasicMap
   private Map<B, Integer> myMap = new HashMap<B, Integer>();

}

@Entity
class B {
 ...
}

From stackoverflow

• I found out that this is not possible, as BasicMap only works for primary datatypes.