Compound Primary key : Column « JPA

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Java Tutorial » JPA » Column

22.21.9.Compound Primary keyPrevious/Next

File: Student.java

import java.io.Serializable;



import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.IdClass;



@Entity

@IdClass(StudentId.class)

public class Student {

    @Id private String country;

    @Id

    @Column(name="EMP_ID")

    private int id;

    private String name;





    public int getId() {

        return id;

    }

    

    public void setId(int id) {

        this.id = id;

    }

    

    public String getCountry() {

        return country;

    }



    public void setCountry(String country) {

        this.country = country;

    }



    public String getName() {

        return name;

    }

    

    public void setName(String name) {

        this.name = name;

    }

    public String toString() {

        return "Student id: " + getId() + " name: " + getName() +

               " country: " + getCountry();

    }

}

class StudentId implements Serializable {

    private String country; 

    private int id; 



    public StudentId() {}

    public StudentId(String country, int id) {

      this.country = country;

      this.id = id;

    }



    public String getCountry() { return country; }

    public int getId() { return id; }



    public boolean equals(Object o) { 

        return ((o instanceof StudentId) && 

                country.equals(((StudentId)o).getCountry()) &&

                id == ((StudentId) o).getId());



    }



    public int hashCode() { 

        return country.hashCode() + id; 

    }

}

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();



    Student emp = new Student();

    emp.setCountry("country");

    emp.setId(1);

    emp.setName("Jack");

    em.persist(emp);

    

    

    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>

Download: JPA-CompoundPrimarykey.zip( 5,288 k)

22.21.Column
	22.21.1.	Unique, Not Nullable Column
	22.21.2.	Specify Column Definition To Field
	22.21.3.	Set Precision And Scale
	22.21.4.	Set Column Length
	22.21.5.	Java String Mapped To Varchar
	22.21.6.	Java Long Mapped To Big Int
	22.21.7.	Java Int Mapped To Integer
	22.21.8.	Use Varchar Type As Column Type
	22.21.9.	Compound Primary key
	22.21.10.	Change Default Column Name

Compound Primary key : Column « JPA « Java Tutorial