CODEWITHSUNDEEP
javahibernatejpa
ohyun
ohyun

Reputation: 41

JPA with Hibernate 4.x, @ElementCollection, Primary Key

I am using JPA with Hibernate 4.x., and postgresql 9.x, but I wonder some problem.

When using @ElementCollection annotation, and I configured Set type embedded field, I expect to generate Primary key of embeddable Collection Table, but it's not working. I can find just one foreign key against owner of relationship. i wonder why do not it generate primary key. This is my test code. A.java

@Entity
public class A {
    @Id
    private Long id;
    @Column(name = "\"as\"")
    private String as;
    public String getAs() {
        return as;
    }

    public void setAs(String as) {
        this.as = as;
    }

    @ElementCollection
    private Set<B> bs = new HashSet<>();

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Set<B> getBs() {
        return bs;
    }

    public void setBs(Set<B> bs) {
        this.bs = bs;
    }
}

B.java

@Embeddable
public class B {
    private String col1;
    private String col2;

    public String getCol1() {
        return col1;
    }

    public void setCol1(String col1) {
        this.col1 = col1;
    }

    public String getCol2() {
        return col2;
    }

    public void setCol2(String col2) {
        this.col2 = col2;
    }
}

the result is

Hibernate: 
    create table A (
        id int8 not null,
        "as" varchar(255),
        primary key (id)
    )
Hibernate: 
    create table A_bs (
        A_id int8 not null,
        col1 varchar(255),
        col2 varchar(255)
    )
Hibernate: 
    alter table A_bs 
        add constraint FK_rcecll1ao3brmwwnsep3iqq3p 
        foreign key (A_id) 
        references A

Let me know why it did not generate primary key? Thanks in advance~

Upvotes: 2

Views: 3758

Answers (2)

o_nvk
o_nvk

Reputation: 56

To generate a primary key for an embeddable collection like Set need to mark all columns of embeddable class with annotation @Column(nullable = false), due to requirement that nullable fields could not be a part of composite primary key

Upvotes: 0

Predrag Maric
Predrag Maric

Reputation: 24423

Because @ElementCollection is used for mapping collections of simple elements, which is not the same as entities. The only thing they need is a reference to owning entity which is properly generated by Hibernate (column A_id and foreign key (A_id) references A). Take a look at this post for more information.

If you really need a primary key in the embeddable object, consider making it a proper entity.

Upvotes: 1

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