Description Alex Mortimer 2016-06-07 16:41:31 EDT

When one entity defines two separate ManyToMany relationships of the same entity type, a join table is created containing three columns. 

Here is an example:

public class EntityA {

@ManyToMany
private List<EntityB> list1;

@ManyToMany
private List<EntityB> list2;

}

This results in EclipseLink creating the following join table:

CREATE TABLE ENTITYA_ENTITYB (EntityA_ID INTEGER NOT NULL, list1_ID INTEGER NOT NULL, list2_ID INTEGER NOT NULL, PRIMARY KEY (EntityA_ID, list1_ID, list2_ID))

The issue is that EclipseLink is creating the join table's columns with a NOTNULL constraint. Then, when EclipseLink inserts values into the table, it will only insert values for two of the columns at a time and will leave the third value as null.  This causes an SQLException since the table columns are created with a NOTNULL constraint.