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Question

How to create an entity with a composite primary key containing a generated value.

Answer 1

A:

You can use foreign key in embedded id as a separate read-only column:

@Entity 
public class Entity2 { 

    @EmbeddedId 
    private Entity2PK pk = new Entity2PK(); 

    @ManyToOne 
    @JoinColumn(name = "entity1_id")
    private Entity1 entity; 

    ... 
} 

@Embeddable 
public class Entity2PK implements Serializable { 

    @GeneratedValue 
    private Long id; 

    @Column(name = "entity1_id", insertable = false, updateable = false)
    private Long entity1Id;

}

axtavt 2010-06-07 11:36:54

I tried your solution but unfortunately can't make it work : Caused by: org.hibernate.MappingException: Repeated column in mapping for entity: test.Entity2 column: entity1_id (should be mapped with insert="false" update="false")

David 2010-06-09 10:03:24

@David: Note the `insertable = false, updateable = false` in `Entity2PK`.

axtavt 2010-06-09 10:48:37

Answer 2

A:

Do as follows whether you want this kind of behavior (You nedd to use property access instead of field one)

Parent.class (Notice a property of Type MutableInt and addChild as a way to set up both sides)

@Entity
public class Parent implements Serializable {

    private MutableInt id = new MutableInt();

    private List<Child> childList = new ArrayList();

    @OneToMany(mappedBy="parent")
    @JoinColumn(name="PARENT_ID", insertable=false, updatable=false)
    @Cascade(CascadeType.SAVE_UPDATE)
    public List<Child> getChildList() {
        return childList;
    }

    public void setChildList(List<Child> childList) {
        this.childList = childList;
    }

    @Id
    @GeneratedValue
    public Integer getId() {
        return id.intValue();
    }

    public void setId(Integer id) {
        this.id.setValue(id);
    }

    @Transient
    public MutableInt getIdAsMutableInt() {
        return id;
    }

    /**
     * Add convenience method 
     * 
     * A way to set up both sides (You have a bi-directional relationship, right ???)
     */
    public void addChild(Child child) {
        if(child.getChildId() == null)
            child.setChildId(new Child.ChildId());

        child.getChildId().setParentIdAsMutableInt(id);

        getChildList().add(child);

        child.setParent(this);
    }

}

Child.class (Notice static inner class )

@Entity
public class Child implements Serializable {

    private ChildId childId;

    private Parent parent;

    @EmbeddedId
    public ChildId getChildId() {
        return childId;
    }

    public void setChildId(ChildId childId) {
        this.childId = childId;
    }

    @ManyToOne
    @JoinColumn(name="PARENT_ID", insertable=false, updatable=false)
    public Parent getParent() {
        return parent;
    }

    public void setParent(Parent parent) {
        this.parent = parent;
    }

    /**
      * Composite primary key class MUST override equals and hashCode
      */
    @Embeddable
    public static class ChildId implements Serializable {

        private MutableInt parentId = new MutableInt();

        private Integer chId;

        public void setParentIdAsMutableInt(MutableInt parentId) {
            this.parentId = parentId;
        }

        @GeneratedValue
        public Integer getChId() {
            return chId;
        }

        public void setChId(Integer chId) {
            this.chId = chId;
        }

        @Column(name="PARENT_ID")
        public Integer getParentId() {
            return parentId.intValue();
        }

        public void setParentId(Integer parentId) {
            this.parentId.setValue(parentId);
        }

        @Override
        public boolean equals(Object o) {
            if(!(o instanceof ChildId))
                return false;

            final ChildId other = (ChildId) o;
            return new EqualsBuilder()
                       .append(getChId(), other.getChId())
                       .append(getParentId(), other.getParentId()).isEquals();
        }

        @Override
        public int hashCode() {
            int hash = 5;
            hash = 11 * hash + getParentId().hashCode();
            hash = 11 * hash + getChId().hashCode();
            return hash;
        }

    }

}

And to test

Session session = configuration.buildSessionFactory().openSession();
session.beginTransaction();

Parent parent = new Parent();
parent.addChild(new Child());

session.save(parent);

session.getTransaction().commit();

You need a MutableInt because of Integer is immutable instance. But your MutableInt field is encapsulated by a Integer property. See carefully

Arthur Ronald F D Garcia 2010-06-07 16:33:59

Thanks for your solution but I find it tedious. Why can't it be as simple as the code I've made ?

David 2010-06-09 09:52:17

@David If you really want this kind of behavior, you should do as shown. Keep in mind: if your @Entity needs a composite primary key, such as Child, you **should** provide a composite primary key class and **must** override equals and hashCode - See ChildId class. add convenience method - see Parent class - Takes care of setting up both sides of The bi-directional relationship.

Arthur Ronald F D Garcia 2010-06-09 12:18:49

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How to create an entity with a composite primary key containing a generated value.

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