Tags: Hibernate , one-to-one

We all understand one-to-one relation in database but when it comes to Hibernate I always stuck at which annotation to use and where should I place it?

We are going to understand the hibernate one-to-one relationship on following table structure.
- country table holds the one-to-one relationship with languages table. Where relationship id resides in country table.
- country table holds the one-to-one relationship with capital table. Where relationship id resides in capital table.


Before we see the complete code, lets first understand how to define relationship in code.

Country.java (country - languages)


Capital.java (country - capital)


Source code (Country.java)

import java.io.Serializable;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

/**
 * @author javaQuery
 * @date 11th April, 2017
 * @Github: https://github.com/javaquery/Examples
 */
@Entity
@Table(name = "country")
public class Country implements Serializable {

    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;

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

    @OneToOne(cascade = CascadeType.ALL, mappedBy = "country")
    private Capital capital;

    @OneToOne
    @JoinColumn(name = "primary_language_id", referencedColumnName = "id")
    private Language language;
 
    //getter-setter
}

Source code (Language.java)

import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 * @author javaQuery
 * @date 1th April, 2017
 * @Github: https://github.com/javaquery/Examples
 */
@Entity
@Table(name = "languages")
public class Language implements Serializable{
    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    
    @Column(name = "language")
    private String language;
 
    //getter-setter
}

Source code (Capital.java)

import java.io.Serializable;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;
import javax.persistence.Table;

/**
 * @author javaQuery
 * @date 11th April, 2017
 * @Github: https://github.com/javaquery/Examples
 */
@Entity
@Table(name = "capital")
public class Capital implements Serializable{
    
    @Id
    @GeneratedValue
    @Column(name = "id")
    private Long id;
    
    @Column(name = "name")
    private String name;

    
    @OneToOne
    @JoinColumn(referencedColumnName = "id", name = "country_id")
    private Country country;
 
    //getter-setter
}

Source code (OneToOneMappingExample.java)

import com.javaquery.bean.Country;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

/**
 * @author javaQuery
 * @date 11th April, 2017
 * @Github: https://github.com/javaquery/Examples
 */
public class OneToOneMappingExample {

    public static void main(String[] args) {
        try {
            /* Create hibernate configuration. */
            Configuration configuration = new Configuration();
            configuration.configure("com\\javaquery\\database\\hibernate\\hibernate.cfg.xml");

            /* Open session and begin database transaction for database operation. */
            SessionFactory sessionFactory = configuration.buildSessionFactory();
            Session session = sessionFactory.openSession();
            
            Country country = session.load(Country.class, 1L);
            System.out.println(country);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Output

Hibernate: 
    select
        country0_.id as id1_1_0_,
        country0_.primary_language_id as primary_3_1_0_,
        country0_.name as name2_1_0_,
        language1_.id as id1_2_1_,
        language1_.language as language2_2_1_,
        capital2_.id as id1_0_2_,
        capital2_.country_id as country_3_0_2_,
        capital2_.name as name2_0_2_ 
    from
        country country0_ 
    left outer join
        languages language1_ 
            on country0_.primary_language_id=language1_.id 
    left outer join
        capital capital2_ 
            on country0_.id=capital2_.country_id 
    where
        country0_.id=?

Country{id=1, name=India, capital=Capital{id=2, name=Delhi}, language=Language{id=2, language=Hindi}}

Tags: Hibernate , one-to-one