<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<entity-mappings xmlns="http://java.sun.com/xml/ns/persistence/orm" version="1.0">
    <persistence-unit-metadata>
    </persistence-unit-metadata>
    <entity name="ClassA" class="hibernatetestapp.ClassA">
        <table name="class_a"/>
        <attributes>
            <id name="classAId">
                <column name="ClassA_Id"/>
                <generated-value strategy="IDENTITY"/>
            </id>
            <basic name="classAValue">
                <column name="ClassA_Value"/>
            </basic>
            <one-to-many name="classBCollection" fetch="EAGER">
                <join-column name="ClassA_Ref" referenced-column-name="ClassA_Id"/>
                <cascade>
                    <cascade-all/>
                </cascade>
            </one-to-many>
        </attributes>
    </entity>
    <entity name="ClassB" class="hibernatetestapp.ClassB" metadata-complete="true">
        <table name="class_b"/>
        <attributes>
            <id name="classBId">
                <column name="ClassB_Id"/>
                <generated-value strategy="IDENTITY"/>
            </id>
            <basic name="classBValue" optional="false">
                <column name="ClassB_Value"/>
            </basic>
        </attributes>
    </entity>
</entity-mappings>

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" 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_1_0.xsd">
  <persistence-unit name="HibernateTestAppPU" transaction-type="RESOURCE_LOCAL">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
    <mapping-file>META-INF/orm.xml</mapping-file>
    <class>hibernatetestapp.ClassA</class>
    <class>hibernatetestapp.ClassB</class>
    <properties>
      <property name="hibernate.connection.username" value="root"/>
      <property name="hibernate.connection.driver_class" value="com.mysql.jdbc.Driver"/>
      <property name="hibernate.connection.password" value="admin"/>
      <property name="hibernate.connection.url" value="jdbc:mysql://localhost:3306/HibernateTest"/>
      <property name="hibernate.cache.provider_class" value="org.hibernate.cache.NoCacheProvider"/>
    </properties>
  </persistence-unit>
</persistence>

--
-- Table structure for table `class_a`
--

DROP TABLE IF EXISTS `class_a`;
CREATE TABLE `class_a` (
  `ClassA_Id` int(10) unsigned NOT NULL auto_increment,
  `ClassA_Value` varchar(45) NOT NULL,
  PRIMARY KEY  (`ClassA_Id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `class_a`
--


/*!40000 ALTER TABLE `class_a` DISABLE KEYS */;
LOCK TABLES `class_a` WRITE;
UNLOCK TABLES;
/*!40000 ALTER TABLE `class_a` ENABLE KEYS */;

--
-- Table structure for table `class_b`
--

DROP TABLE IF EXISTS `class_b`;
CREATE TABLE `class_b` (
  `ClassB_Id` int(10) unsigned NOT NULL auto_increment,
  `ClassB_Value` varchar(45) default NULL,
  `ClassA_Ref` int(10) unsigned default NULL,
  PRIMARY KEY  (`ClassB_Id`),
  KEY `FK_Class_B_1` (`ClassA_Ref`),
  CONSTRAINT `FK_Class_B_1` FOREIGN KEY (`ClassA_Ref`) REFERENCES `class_a` (`ClassA_Id`) ON DELETE NO ACTION ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

--
-- Dumping data for table `class_b`
--

SET FOREIGN_KEY_CHECKS=1;

package hibernatetestapp;

import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.Id;

/**
*
* @author kiril.kalchev
*/
public class ClassA implements Serializable {
    private static final long serialVersionUID = 1L;
    //@Id
    private Integer classAId;
    private String classAValue;
    private Set<ClassB> classBCollection;

    public ClassA() {
        this(null, null);
    }

    public ClassA(Integer classAId) {
        this(classAId, null);
    }

    public ClassA(Integer classAId, String classAValue) {
        this.classAId = classAId;
        this.classAValue = classAValue;
        classBCollection = new HashSet<ClassB>();
    }

    public Integer getClassAId() {
        return classAId;
    }

    public void setClassAId(Integer classAId) {
        this.classAId = classAId;
    }

    public String getClassAValue() {
        return classAValue;
    }

    public void setClassAValue(String classAValue) {
        this.classAValue = classAValue;
    }

    public Set<ClassB> getClassBCollection() {
        return classBCollection;
    }

    public void setClassBCollection(Set<ClassB> classBCollection) {
        this.classBCollection = new HashSet<ClassB>(classBCollection);
    }

    @Override
    public String toString() {
        return "hibernatetestapp.ClassA[classAId=" + classAId + "]";
    }

}

package hibernatetestapp;

import java.io.Serializable;

/**
*
* @author kiril.kalchev
*/

public class ClassB implements Serializable {
    private static final long serialVersionUID = 1L;

    private Integer classBId;

    private String classBValue;

    public ClassB() {
    }

    public ClassB(Integer classBId) {
        this.classBId = classBId;
    }

    public ClassB(Integer classBId, String classBValue) {
        this.classBId = classBId;
        this.classBValue = classBValue;
    }

    public Integer getClassBId() {
        return classBId;
    }

    public void setClassBId(Integer classBId) {
        this.classBId = classBId;
    }

    public String getClassBValue() {
        return classBValue;
    }

    public void setClassBValue(String classBValue) {
        this.classBValue = classBValue;
    }

    @Override
    public String toString() {
        return "hibernatetestapp.ClassB[classBId=" + classBId + "]";
    }

}

package hibernatetestapp;

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

/**
*
* @author kiril.kalchev
*/
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        ClassB b1 = new ClassB(null, "B1");
        ClassB b2 = new ClassB(null, "B2");
        ClassA a1 = new ClassA(null, "A1");
        a1.getClassBCollection().add(b2);
        a1.getClassBCollection().add(b1);
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("HibernateTestAppPU");
        ClassA attached = persistObject(emf, a1);
        ClassA getted = getClassAObject(emf, attached);
        System.out.println(getted.getClassBCollection());
    }

    private static ClassA getClassAObject(EntityManagerFactory emf, ClassA attached) {
        EntityManager em = emf.createEntityManager();
        ClassA getted = em.find(ClassA.class, attached.getClassAId());
        em.close();
        return getted;
    }

    private static ClassA persistObject(EntityManagerFactory emf, ClassA a1) {
        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();
        em.persist(a1);
        em.getTransaction().commit();
        em.close();
        return a1;
    }

}