How to join fields of two tables using Hibernate?

Question

I have two tables and related Java mapping.

CREATE TABLE country (
    code VARCHAR(3) PRIMARY KEY NOT NULL,
    name VARCHAR(100) NOT NULL
);


CREATE TABLE user (
    id INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
    name VARCHAR(100) NOT NULL,
    country_code VARCHAR(3),
    FOREIGN KEY ( country_code ) REFERENCES country ( code )
);

Here is my Java entities. Country POJO:

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

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

    @Column (name = "name")
    private String name;

And User POJO:

@Entity
@Table(name = "user")
public class User implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "name")
    private String name;

    @Column(name = "country_code")
    private String countryCode;

Question is how can I join Contry.code to User.countryCode in Hibernate using annotation? When I create User object with Hibernate I need to bind these two fields (code and countryCode) automatically.

Rohit Jain · Accepted Answer · 2014-03-11 19:30:54Z

2

You need @OneToMany mapping from Country to User entity and corresponding @ManyToOne mapping from User to Country:

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

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

    @Column (name = "name")
    private String name;

    @OneToMany(mappedBy = "country")
    private Set<User> users;
}

@Entity
@Table(name = "user")
public class User implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @Column(name = "name")
    private String name;

    @ManyToOne
    @JoinColumn(name = "country_code")
    private Country country;
}

answered Mar 11, 2014 at 19:30

Rohit Jain

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3 Comments

user3279337 Over a year ago

But I need just a countryCode not Country object.

Rohit Jain Over a year ago

@user3279337 This is how you create mapping between entities in hibernate. You can get countryCode from the country reference.

Rohit Jain Over a year ago

@user3279337 BTW, this is just a very basic mapping. There are many more options you can give. You might want to go through hibernate documentation for more information on this.

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