When you try to automatically generate classes from database tables, if there is
a join table involved, Netbeans always creates a @ManytoMany annotation which is
not always the desired behaviour.

To reproduce:

1) Create database schema (ie in Oracle)

  create table A (a1 integer, a2 date, primary key (a1));
  create table B (b1 integer, b2 date, primary key (b1));
  create table A_B (a1 integer not null, b1 integer not null);
  alter table A_B add constraint uniqueB unique(b1);
  alter table A_B add constraint ab foreign key (a1) references A(a1);
  alter table A_B add constraint ba foreign key (b1) references B(b1);

2) Select New->Entity classes from Database
3) Look at the inferred code. The unique constraint that specifies a @OnetoMany
relationship between A and B couldn't be correctly processed.