Hibernate Bi-Directional One to One mapping using Annotations

It took me more than few minutes to find how to do one to one mapping using Hibernate Annotations, so I though I will share it.

I think Hibernate Annotations is best explained by example. Actually, I am not sure I have ever read anything about Hibernate Annotation mappings beside looking at examples…

This example is built from 2 classes: Person and PersonDetails, corresponding to 2 database tables: person and person_details. The 2 classes will demonstrate the usage of one to one mapping from both directions.

I am not sure this example is so close to the real world, but I believe it is enough to get the idea.

The person table contains the following columns:

• person_id – used as primary key with auto increment
• first_name
• last_name
• birth_date

The person_details table contains the following columns:

• person_id – used as primary key and foreign key to person table (person_id column)
• weight
• height
• hair_color
• eyes_color

Note that there may be persons with no person details. That means that having a row in person table, but no row in person_details table is a trivial case. Of course that there may be at the most one person details row for each person.

This is how the Person class looks like using Hibernate Annotations:

package com.bashan.hibernate;
import org.hibernate.validator.Length;
import org.hibernate.validator.NotNull;
import javax.persistence.*;
import java.io.Serializable;
import java.util.Date;
@Entity
@Table(name="person")
public class Person implements Serializable {
  @Id
  @GeneratedValue(strategy= GenerationType.AUTO)
  @Column(name="person_id")
  private Integer personId;
  @Column(name="first_name")
  @NotNull
  @Length(max = 50)
  private String firstName;
  @Column(name="last_name")
  @NotNull
  @Length(max = 50)
  private String lastName;
  @Column(name="birth_date")
  private Date birthDate;
  @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "person")
  @JoinColumn(name="person_id")
  private PersonDetails personDetails;
  public Integer getPersonId() {
    return personId;
  }
  public void setPersonId(Integer personId) {
    this.personId = personId;
  }
  public String getFirstName() {
    return firstName;
  }
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  public String getLastName() {
    return lastName;
  }
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  public Date getBirthDate() {
    return birthDate;
  }
  public void setBirthDate(Date birthDate) {
    this.birthDate = birthDate;
  }
  public PersonDetails getPersonDetails() {
    return personDetails;
  }
  public void setPersonDetails(PersonDetails personDetails) {
    this.personDetails = personDetails;
  }
}

And the PersonDetails class:

package com.bashan.hibernate;
import org.hibernate.annotations.Cascade;
import org.hibernate.annotations.GenericGenerator;
import org.hibernate.annotations.Parameter;
import javax.persistence.*;
@Entity
@Table(name="person_details")
public class PersonDetails {
  @Id
  @GeneratedValue(generator="foreign")
    @GenericGenerator(name="foreign", strategy = "foreign", parameters={
      @Parameter(name="property", value="person")
    })
  @Column(name="person_id")
  private Integer personId;
  @OneToOne(fetch = FetchType.LAZY, optional=true)
  @Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})
  @PrimaryKeyJoinColumn
  private Person person;
  @Column(name="weight")
  private Integer weight;
  @Column(name="height")
  private Integer height;
  @Column(name="hair_color")
  private Integer hardColor;
  @Column(name="eyes_color")
  private Integer eyesColor;
  public Integer getPersonId() {
    return personId;
  }
  public void setPersonId(Integer personId) {
    this.personId = personId;
  }
  public Person getPerson() {
    return person;
  }
  public void setPerson(Person person) {
    this.person = person;
  }
  public Integer getWeight() {
    return weight;
  }
  public void setWeight(Integer weight) {
    this.weight = weight;
  }
  public Integer getHeight() {
    return height;
  }
  public void setHeight(Integer height) {
    this.height = height;
  }
  public Integer getHardColor() {
    return hardColor;
  }
  public void setHardColor(Integer hardColor) {
    this.hardColor = hardColor;
  }
  public Integer getEyesColor() {
    return eyesColor;
  }
  public void setEyesColor(Integer eyesColor) {
    this.eyesColor = eyesColor;
  }
}

That’s pretty much it… I hope it will save you time…