The many-to-many unidirectional relationship differs from the many-to-many bidirectional relationship by the missing field of type java.util.Set on one of the sides.
The relational model is the same as the relational model for many-to-many bidirectional relationships.
The mapping metadata for the remaining field of type java.util.Set is the same as the mapping in the many-to-many bidirectional case, except that the property update in the relationship field must not be set to false.
See also:
Many-to-Many Bidirectional Relationships