Id Containing Relationship : Primary Key « JPA « Java Tutorial

1. Java Tutorial
2. JPA
3. Primary Key

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 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();


    


    em.getTransaction().commit();
    em.close();
    emf.close();

    Helper.checkData();
  }
}

File: Project.java

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Entity 
@IdClass(ProjectId.class)
public class Project {
    @Id
    @Column(name="Student_ID", insertable=false, updatable=false)
    private int studentId;
    @Id private String name;

    @ManyToOne
    @JoinColumn(name="Student_ID")
    private Student student;

    @Temporal(TemporalType.DATE)
    @Column(name="START_DATE")
    private Date startDate;
    @Temporal(TemporalType.DATE)
    @Column(name="END_DATE")
    private Date endDate;

    public Project() {}
    public Project(Student student) {
        this.student = student;
        this.studentId = student.getId();
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String projectName) {
        this.name = projectName;
    }
    
    public int getDeptId() {
        return studentId;
    }
    
    public Student getStudent() {
        return student;
    }
    
    public Date getEndDate() {
        return endDate;
    }
    
    public void setEndDate(Date endDate) {
        this.endDate = endDate;
    }
    
    public Date getStartDate() {
        return startDate;
    }
    
    public void setStartDate(Date startDate) {
        this.startDate = startDate;
    }
    
    public String toString() {
        return "Project name: " + getName();
    }
}

File: ProjectId.java

import java.io.Serializable;

public class ProjectId implements Serializable {
    private int studentId;
    private String name;

    public ProjectId() {}
    public ProjectId(int deptId, String name) {
        this.studentId = deptId;
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public int getId() {
        return studentId;
    }

    public boolean equals(Object o) {
        return ((o instanceof ProjectId) && 
                name.equals(((ProjectId) o).getName()) && 
                studentId == ((ProjectId) o).getId());

    }

    public int hashCode() {
        return name.hashCode() + studentId;
    }
}

File: Student.java

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

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Student {
    @Id
    private int id;
    private String name;
    @OneToMany(mappedBy="student")
    private Collection<Project> projects;

    public Student() {
        projects = new ArrayList<Project>();
    }
    
    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 Collection<Project> getProjects() {
        return projects;
    }

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

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>

22.19.Primary Key
	22.19.1.	Use UUID As Primary Key
	22.19.2.	Use Current Milisecond As ID
	22.19.3.	Set Primary Key Join Column For Entities In Hierarchy
	22.19.4.	Set ID By Yourself
	22.19.5.	Not Nullable ID
	22.19.6.	ID Entity With Hash Code And Equals
	22.19.7.	Id Containing Relationship
	22.19.8.	Embedded Compound Primary Key
	22.19.9.	Define Extra Class For Compound Key