CODEWITHSUNDEEP
javahibernatejpa
mollwitz
mollwitz

Reputation: 223

Mapping a weak entity with JPA

My database contains a companies and employees. I have modeled Employee as a weak entity of Company.

My JPA annotations look like:

@Entity
public class Company extends Model {

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

    @OneToMany(mappedBy = "company", cascade = CascadeType.ALL)
    private List<Employee> employees;

}

Employee.java:

@Entity
public class Employee extends Model {

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

    @ManyToOne(optional = false)
    @JoinColumn(name="company_id", insertable=false, updatable=false)
    private Company company;
}

The following SQL code is created:

create table employee (
  id                            bigint auto_increment not null,
  company_id                    bigint not null,
  constraint pk_employee primary key (id)
);

alter table employee add constraint fk_employee_company_id foreign key (company_id) references company (id) on delete restrict on update restrict;

What I want is (constraint pk_employee primary key (id, company_id):

create table employee (
  id                            bigint auto_increment not null,
  company_id                    bigint not null,
  constraint pk_employee primary key (id, company_id)
);

alter table employee add constraint fk_employee_company_id foreign key (company_id) references company (id) on delete restrict on update restrict;

Is there a way to create such SQL script?

EDIT: Letting Employee implement Serializable does not do the trick.

Caused by: javax.persistence.PersistenceException: Could not find BeanDescriptor for class models.Company. Perhaps the EmbeddedId class is not registered?
    at io.ebeaninternal.server.deploy.BeanEmbeddedMetaFactory.create(BeanEmbeddedMetaFactory.java:26)
    at io.ebeaninternal.server.deploy.BeanPropertyAssocOne.<init>(BeanPropertyAssocOne.java:79)
    at io.ebeaninternal.server.deploy.BeanPropertyAssocOne.<init>(BeanPropertyAssocOne.java:62)
    at io.ebeaninternal.server.deploy.meta.DeployBeanTable.createProperty(DeployBeanTable.java:68)
    at io.ebeaninternal.server.deploy.meta.DeployBeanTable.createIdProperties(DeployBeanTable.java:59)
    at io.ebeaninternal.server.deploy.BeanTable.<init>(BeanTable.java:42)

Upvotes: 3

Views: 4936

Answers (2)

magdi amer
magdi amer

Reputation: 66

Thanks to @Alan Hay for giving us the link https://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Composite_Primary_Keys

Here is how you create a weak entity Address that takes it's Id (user_id) from the table pmo_user 

pmo_user{id, ....}
test_address{user_id, address}

============================

@Entity
@Table(name="test_address")
public class Address 
{
    @Id
    @Column(name="user_id")
    protected int userId;

    @OneToOne
    @PrimaryKeyJoinColumn(name="user_id", referencedColumnName="id")
    protected PmoUser owner;

    @Column(name="address")
    protected String address;


    public void setOwner(PmoUser owner) 
    {
        this.owner = owner;
        this.userId = owner.getId();
    }


    @Override
    public String toString() {
        return "Address [userId=" + userId + ", owner=" + owner + ", address=" + address + "]";
    }    

}

Upvotes: 2

Angga
Angga

Reputation: 2323

Just add @Id annotation under your @JoinColumn annotation. But Employee class must implements Serializable to use this solution.

Upvotes: 0

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