Hibernate中与同一类的多个一对多/一对一关系

Question

Say I have a Person, Building, and Address class. A person can have many addresses and a building can have one address. In the DB, all three have their own separate table. The way the Address table is linked is by using a fk_id column and a type column. An address for a person is stored by storing the person_id as the fk_id and setting type to "person", whereas for a building you store the building_id as fk_id and set the type to "building". Is there any way to map these relationships or would I need to either convert the DB to use a linking table and do a many-to-many or just use HQL to retrieve that data?

Answer 1

You can map your entities like this.

<class name="Address">
    <id name="addressId" column="addressId">
       <generator class="native"/>
    </id>
</class>

<class name="Person">
    <id name="personId" column="personId">
       <generator class="native"/>
    </id>
   <set name="addresses" table="PersonAddress">
       <key column="personId"/>
       <many-to-many column="addressId"
         unique="true"
         class="Address"/>
   </set>
</class>

<class name="Building">
    <id name="id" column="buildingId">
       <generator class="native"/>
    </id>
   <many-to-one name="address" 
      column="addressId" 
      unique="true"
      not-null="true"/>
</class>

U just need an extra table PersonAddress.

Answer 2

You could map this as so:

@Entity
public class Address {
  @ManyToOne @JoinColumn(name="person_id")
  private Person person;

  @OneToOne @JoinColumn(name="building_id")
  private Building building;
}

@Entity
public class Person {
  @OneToMany(mappedBy="person", targetEntity=Address.class)
  private Set<Address> addresses;
}

@Entity
public class Building {
  @OneToOne(mappedBy="building")
  private Address address;
}

In this example, address could have either a Person or a Building (it should not have both). Also, Address is considered the owner of the relationship, and Person or Building is the "inverse" side of that relationship.

That being said, to create the object graph, you could still use cascading saves (the "cascade" attribute on the annotations) so that you could create all the objects in memory, and simply save the Person or Building, and it should automagically save the Address objects along with it.

Answer 3

找到答案后，所需要做的就是在集合上添加一个“ where”条件。