JPA 2 - Foreign key that only includes one field from a composite primary key?

Question

I'm having trouble getting a composite primary key and foreign keys working in JPA 2/Hibernate. I'm trying to create a simple scenario with countries and provinces:

Country Entity:

@Entity
@Table(name = "country")
public class Country extends DomainObjectBase implements Serializable {

    @Id
    @Basic(optional = false)
    @Column(name = "code")
    private String code;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "country")
    private List<Province> provinces;
}

Province Primary Key:

@Embeddable
public class ProvincePK implements Serializable {

    @Basic(optional = false)
    @Column(name = "code")
    private String code;

    @Basic(optional = false)
    @Column(name = "country_code")
    private String countryCode;
}

Province Entity:

@Entity
@Table(name = "province")
public class Province extends DomainObjectBase implements Serializable {

    @EmbeddedId
    protected ProvincePK provincePK;

    @MapsId("country_code")
    @JoinColumn(name = "country_code", referencedColumnName = "code", insertable = false, updatable = false)
    @ManyToOne(optional = false)
    private Country country;
}

This create the correct tables for me with one exception:

Country Table:

1. code PK
2. ...

Province Table

1. code PK FK - This is where the problem is its creating a foreign key reference to the country table's code column
2. country_code FK This is the only foreign key reference I want
3. ...

How do I map my entities/composite key for hibernate to generate the schema I want? Right now I can't insert any data into province because its expecting that country contains the province code!

Thanks for any help.

Answer 1

Try this. I've found that it works for me when I work with data models like this.

@Entity
@Table(name = "province")
@IdClass(ProvincePK.class)
public class Province extends DomainObjectBase implements Serializable {
        
    @Id
    @Basic(optional = false)
    @Column(name = "code")
    private String code;
    
    @Id
    @Basic(optional = false, insertable = false, updatable = false)
    @Column(name = "country_code")
    private String countryCode;
            
    @JoinColumn(name = "country_code", referencedColumnName = "code")
    @ManyToOne
    private Country country;
}

Answer 2

@MapsID argument must match to the name of attribute in ProvincePK class. @JoinColumn should be marked insertable=true,updatable=true, then it works. Here is the code -

@Entity
@Table(name = "province")
public class Province  implements Serializable {

    @EmbeddedId
    protected ProvincePK provincePK;

    @MapsId(value = "country_code")
    @JoinColumn(name = "country_code", referencedColumnName = "code")
    @ManyToOne(optional = false)
    private Country country;
}

@Embeddable
public class ProvincePK implements Serializable {

    @Basic(optional = false)
    @Column(name = "code")
    private String code;

    @Basic(optional = false)
    @Column(name = "country_code")
    private String country_code;
}

@Entity
@Table(name = "country")
public class Country  implements Serializable {

    @Id
    @Basic(optional = false)
    @Column(name = "code")
    private String code;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "country")
    private List<Province> provinces;
}

Hope it helps.