Extra columns in table used in @JoinTable annotation

Question

I'm creating a REST API using Spring Boot and Hibernate.

I have two tables, let's call them table Foo and table Bar. They have an 1-N association that is mapped through a third table, let's call it FooBarAssociation. I created this association between them using the @JoinTable annotation.

Here is a minimum example of what I have now.

public class Foo {
    @Id
    @Column(name = "foo_id");
    Long fooId;
}

public class Bar{

    @Id
    @Column(name = "bar_id");
    Long barId;

    @ManyToOne
    @JoinTable(name = "Foo ", joinColumns = @JoinColumn(name = "bar_id"), inverseJoinColumns = @JoinColumn(name = "foo_id"))
    Foo foo;

}

The thing is, the table FooBarAssociation also has a third column that should contain the date that the relation was created. So there are three columns: foo_id, bar_id and date. When hibernate tries to insert a new entry to FooBarAssociation it generates as exception, as the column date does not allow null values. Is there a way I can tell hibernate how to fill this extra column?

insert into FooBarAssociation (foo_id, bar_id) values (?, ?)

Cannot insert the value NULL into column 'date', table 'FooBarAssociation'; column does not allow nulls. INSERT fails.

Answer 1

Well since this relation is manadatory the only way I see to modify middle layer, is to obtain control over it explicitly. This will help.

@Getter
@Setter
@Entity
@NoArgsConstructor
public class Bar {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "bar_id")
    FooBarRelation relation;

    public void setFoo(Foo foo) {
        relation = new FooBarRelation(this, foo);
    }
}

@Getter
@Setter
@Entity
@NoArgsConstructor
@EntityListeners(AuditingEntityListener.class)
public class FooBarRelation {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "foo_id")
    Foo foo;

    @OneToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "bar_id")
    Bar bar;

    @LastModifiedDate
    LocalDateTime dateTime;

    public FooBarRelation(Bar bar, Foo foo) {
        this.bar = bar;
        this.foo = foo;
    }
}


@Getter
@Setter
@Entity
@NoArgsConstructor
public class Foo {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    Long id;
}

Test:

  @Autowired
    public BarRepo barRepo;

    @Test
    public void testBar(){
        Bar bar = new Bar();
        bar.setFoo(new Foo());
        barRepo.save(bar);
        List<Bar> all = barRepo.findAll();
        FooBarRelation relation = all.get(0).getRelation();
        assertNotNull(relation.getBar());
        assertNotNull(relation.getFoo());
        assertNotNull(relation.getDateTime());
    }

Cascade types and other minor details on you ;)