休眠中的COMPOSITE-ID

Question

from

https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/mapping.html

i don't get how to use "composite-id" tag without "class" parameter, and those few example that i manage to Google making things even more messy.

so my example

<class name="mainPack.Point" table="POINT">
    <composite-id>
        <key-property name="x" type="int">
            <column name="X" />
        </key-property>
        <key-property name="y" type="int">
            <column name="Y" />
        </key-property>
    </composite-id>
    <property name="str" type="java.lang.String">
        <column name="STR" />
    </property>
</class>

Will it work?

Will columns

 <column name="X" />
 <column name="Y" /> 

be present in the table?

And will there be created another mapping table containing new "id class", with two parameter "X", "Y"?

Answer 1

1. Will it work?

Yes. I used hibernate-update to create a table, here is result:

CREATE TABLE point
(
  x integer NOT NULL,
  y integer NOT NULL,
  str character varying(255),
  CONSTRAINT point_pkey PRIMARY KEY (x, y)
)

2. Will columns be present in the table?

Yes. You can see it above.

3. And will there be created another mapping table containing new "id class", with two parameter "X", "Y"?

No.

---

Here is java class:

 public class Point implements Serializable { private int x; private int y; private String str; public int getX() { return this.x; } public void setX(int x) { this.x = x; } public int getY() { return this.y; } public void setY(int y) { this.y = y; } public String getStr() { return this.str; } public void setStr(String str) { this.str = str; } @Override public int hashCode() { return new HashCodeBuilder().append(this.x).append(this.y).toHashCode(); } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (!(obj instanceof Point)) { return false; } Point other = (Point) obj; return (this.getX() == other.getX()) && (this.getY() == other.getY()); } 

}

Answer 2

// Composite primary key bean

import java.io.Serializable;

public class CoursePk implements Serializable {

private static final long serialVersionUID = 1L;
private String title;
private String tutor;

public CoursePk(){

}
public String getTitle() {
    return title;
}
public void setTitle(String title) {
    this.title = title;
}
public String getTutor() {
    return tutor;
}
public void setTutor(String tutor) {
    this.tutor = tutor;
}
}


// Course class for composite primary key
@Entity
@Table(name="course")
public class Course implements Serializable {
private static final long serialVersionUID = 1L;

@EmbeddedId                    // composite key
private CoursePk id=null;

private int totalStudents;

public int getTotalStudents() {
    return totalStudents;
}

public void setTotalStudents(int totalStudents) {
    this.totalStudents = totalStudents;
}

public CoursePk getId() {
    return id;
}
public void setId(CoursePk id) {
    this.id = id;
}
}


 // Hibernate Util to get Session factory
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
public class HibernateUtil {
private HibernateUtil(){

}
 private static SessionFactory sessionFactory ;
 static {
    Configuration configuration = new Configuration();

    configuration.addAnnotatedClass (Course.class);
    configuration.setProperty("connection.driver_class","com.mysql.jdbc.Driver");
    configuration.setProperty("hibernate.connection.url", "jdbc:mysql://localhost:3306/hibernate");                                
    configuration.setProperty("hibernate.connection.username", "root");     
    configuration.setProperty("hibernate.connection.password", "root");
    configuration.setProperty("dialect", "org.hibernate.dialect.MySQLDialect");
    configuration.setProperty("hibernate.hbm2ddl.auto", "update");
    configuration.setProperty("hibernate.show_sql", "true");
    configuration.setProperty(" hibernate.connection.pool_size", "10");

    StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties());
    sessionFactory = configuration.buildSessionFactory(builder.build());
 }
public  SessionFactory getSessionFactory() {
    return sessionFactory;
}

public static HibernateUtil getInstance(){
    return new HibernateUtil();
}
} 

// Main Class for testing composite primary key
public class CompositePrimaryKeyTest {
public static void main(String[] args) {
    CoursePk pk=new CoursePk();
    pk.setTitle("Java Book");
    pk.setTutor("Deepak");

    Course course=new Course();
    course.setTotalStudents(100);
    course.setId(pk);
    Session   session=HibernateUtil.getInstance().getSessionFactory().openSession();
    session.beginTransaction();

    session.save(course);

    session.getTransaction().commit();
}
}