One To One Mapping Primary Key As Join Column : One To One Mapping « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. One To One Mapping

File: Department.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.PrimaryKeyJoinColumn;

@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;

    @OneToOne
    @PrimaryKeyJoinColumn//a primary key column that is used as a foreign key to join to another table
    private Student student;
    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String deptName) {
        this.name = deptName;
    }

    public Student getStudent() {
      return student;
    }

    public void setStudent(Student student) {
      this.student = student;
    }

    public String toString() {
        return "Department id: " + getId() + 
               ", name: " + getName();
    }
}

File: Student.java

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToOne;

@Entity
public class Student {
  @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
  private int id;
  private String name;

  @OneToOne (cascade=CascadeType.ALL, mappedBy="student")
  private Department department;

  public int getId() {
    return id;
  }

  public void setId(int id) {
    this.id = id;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }



  public Department getDepartment() {
    return department;
  }

  public void setDepartment(Department department) {
    this.department = department;
  }

  public String toString() {
    return "\n\nID:" + id + "\nName:" + name + "\n\n" + department;
  }
}

File: Helper.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

public class Helper {
  public static void checkData() throws Exception {
    Class.forName("org.hsqldb.jdbcDriver");
    Connection conn = DriverManager.getConnection("jdbc:hsqldb:data/tutorial", "sa", "");
    Statement st = conn.createStatement();

    ResultSet mrs = conn.getMetaData().getTables(null, null, null, new String[] { "TABLE" });
    while (mrs.next()) {
      String tableName = mrs.getString(3);
      System.out.println("\n\n\n\nTable Name: "+ tableName);

      ResultSet rs = st.executeQuery("select * from " + tableName);
      ResultSetMetaData metadata = rs.getMetaData();
      while (rs.next()) {
        System.out.println(" Row:");
        for (int i = 0; i < metadata.getColumnCount(); i++) {
          System.out.println("    Column Name: "+ metadata.getColumnLabel(i + 1)+ ",  ");
          System.out.println("    Column Type: "+ metadata.getColumnTypeName(i + 1)+ ":  ");
          Object value = rs.getObject(i + 1);
          System.out.println("    Column Value: "+value+"\n");
        }
      }
    }
  }
}

File: Main.java

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class Main {
  static EntityManagerFactory emf = Persistence.createEntityManagerFactory("JPAService");
  static EntityManager em = emf.createEntityManager();

  public static void main(String[] a) throws Exception {
    em.getTransaction().begin();
    
    
    Student student = new Student();
    student.setName("Joe");
    em.persist(student);
    
    
    Department dept = new Department();
    dept.setName("dept name");
    student.setDepartment(dept);
    
    
    em.flush();
    


    
    
    
    Query query = em.createQuery("SELECT e FROM Student e");
    List<Student> list = (List<Student>) query.getResultList();
    System.out.println(list);
    
    query = em.createQuery("SELECT d FROM Department d");
    List<Department> dList = (List<Department>) query.getResultList();
    System.out.println(dList);
    
    em.getTransaction().commit();
    em.close();
    emf.close();
    
    Helper.checkData();
  }
}

File: persistence.xml

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence" version="1.0">
  <persistence-unit name="JPAService" transaction-type="RESOURCE_LOCAL">
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.HSQLDialect"/>
      <property name="hibernate.hbm2ddl.auto" value="update"/>
      <property name="hibernate.connection.driver_class" value="org.hsqldb.jdbcDriver"/>
      <property name="hibernate.connection.username" value="sa"/>
      <property name="hibernate.connection.password" value=""/>
      <property name="hibernate.connection.url" value="jdbc:hsqldb:data/tutorial"/>
    </properties>
  </persistence-unit>
</persistence>

22.9.One To One Mapping
	22.9.1.	Retrieve One To One Mapped Entity
	22.9.2.	One To One Unidirectional
	22.9.3.	One To One Mapping With Fetch Type Lazy
	22.9.4.	One To One Mapping With Cascading.All
	22.9.5.	One To One Mapping Primary Key As Join Column
	22.9.6.	One To One Mapping Mapped By Field
	22.9.7.	One To One Mapping Bidirectional
	22.9.8.	One To One Mapping Based On Table Based ID
	22.9.9.	Bidirectional One To One Mapping