如何制作外键？

Question

How can I specify a foreign key in hibernate ?

I have a table A that has id as a column which also forms its primary key. Now the second table B also has id as the column but it should be the foreign key that references the id column of table A .

How can I specify this relation ?

Answer 1

This example is a one to one relation using shared primary key. You can use @PrimaryKeyJoinColumn to achieve this.

In Class A

@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn(name = "ID")
public B getB() {
    return b;
}

In Class B,

@Id
@GenericGenerator(name = "gen", strategy = "foreign", parameters = { @Parameter(name = "property", value = "a") })
@GeneratedValue(generator = "gen")
public Long getId() {
    return id;
}


@OneToOne(mappedBy = "a", cascade = CascadeType.ALL)
public B getB() {
    return b;
}

Answer 2

If you're using annotations you must add the relation and the join column with annotations like these:

@ManyToOne
@JoinColumn(name="id", nullable=false)
public A getA() {
//...
}

if you're using a mapping xml file it's something like this:

<set name="objects" lazy="true" inverse="true" cascade="all-delete-orphan">
    <key column="ID" />
    <one-to-many class="com.objectx.A" />
</set>