Hibernate

Uni-Directional One to Many Relationship using user managed join table

@Entity
@Table(name = "FOO")
public class Foo {
private UUID fooId;

@OneToMany
@JoinTable(
name = "FOO_BAR",
joinColumns = @JoinColumn(name = "fooId"),
inverseJoinColumns = @JoinColumn(name = "barId", unique = true))
private List<Bar> bars;
}

@Entity
@Table(name = "BAR")
public class Bar {
private UUID barId;
// No Mapping specified here.
}

@Entity
@Table(name = "FOO_BAR")
public class FooBar {
private UUID fooBarId;

@ManyToOne
@JoinColumn(name = "fooId")
private Foo foo;

@ManyToOne
@JoinColumn(name = "barId", unique = true)
private Bar bar;
// You can store other objects/fields on this table here.
}

Specifies a one-way relationship between one Foo object to many Bar objects using an intermediate join table that the user manages.

This is similar to a ManyToMany relationship, but if you add a unique constraint to the target foreign key you can enforce that it is OneToMany.

The Foo objects are stored as rows in a table called FOO. The Bar objects are stored as rows in a table called BAR. The relationships between Foo and Bar objects are stored in a table called FOO_BAR. There is a FooBar object as part of the application. 

 Notice that there is no mapping of Bar objects back to Foo objects. Bar objects can be manipulated freely without affecting Foo objects.

 Very commonly used with Spring Security when setting up a User object who has a list of Role's that they can perform. You can add and remove roles to a user without having to worry about cascades deleting Role's.