One To Many List Collection : One To Many Mapping « JPA « Java Tutorial

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

File: Student.java

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

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

    
    @ManyToOne
    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 "Student id: " + getId() + " name: " + getName() + 
               " with " + getDepartment();
    }
}

File: Department.java

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;

@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    @OneToMany(mappedBy="department")
    @OrderBy("name ASC")
    private List<Student> students;

    public Department() {
        students = new ArrayList<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 void addStudent(Student student) {
        if (!getStudents().contains(student)) {
            getStudents().add(student);
            if (student.getDepartment() != null) {
                student.getDepartment().getStudents().remove(student);
            }
            student.setDepartment(this);
        }
    }
    
    public Collection<Student> getStudents() {
        return students;
    }

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

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.addStudent(student);
    em.persist(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>

22.8.One To Many Mapping
	22.8.1.	Use Collection In One To Many Mapping
	22.8.2.	Set target Entity For One To Many Mapping
	22.8.3.	One To Many With Order By Setting
	22.8.4.	One To Many With Mapped By To remove Mapping Table
	22.8.5.	One To Many Map Collection
	22.8.6.	One To Many List Collection
	22.8.7.	One To Many Join Table Setup
	22.8.8.	One To Many Cascade.All
	22.8.9.	One To Many Bidirectional