package test.collection;

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

@Entity
public class Child {

   private Long id;
   private String childName;

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public Long getId() {
      return id;
   }

   public void setId(Long id) {
      this.id = id;
   }

   public String getChildName() {
      return childName;
   }

   public void setChildName(String childName) {
      this.childName = childName;
   }
}

package test.collection;

import java.util.Map;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.MapKey;
import javax.persistence.OneToMany;

@Entity
public class Parent {

   private Long id;
   private String name;
   private Map<String, Child> children;

   @Id @GeneratedValue(strategy=GenerationType.AUTO)
   public Long getId() {
      return id;
   }

   public void setId(Long id) {
      this.id = id;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }

   @OneToMany(cascade=CascadeType.ALL)
   @MapKey(name="childName")
   public Map<String, Child> getChildren() {
      return children;
   }

   public void setChildren(Map<String, Child> children) {
      this.children = children;
   }
   
}

package test.collection;

import java.util.HashMap;
import java.util.Map;

import junit.framework.TestCase;

import org.hibernate.LazyInitializationException;
import org.hibernate.Session;

public class TestIt extends TestCase {

   public void testIt() {
      Long id = createData();
      
      Session session = HibernateUtil.getSession();
      Parent parent = (Parent)session.load(Parent.class, id);
      session.close();
      
      // parent should be a proxy so its fields aren't accessible outside session
      try {
         parent.getName();
         fail("Lazy initialzation exception expected");
      } catch (LazyInitializationException e) {
      }

      try {
         parent.getChildren().size();
         fail("Lazy initialzation exception expected");
      } catch (LazyInitializationException e) {
      }

      // ---------------------
      
      session = HibernateUtil.getSession();
      parent = (Parent)session.load(Parent.class, id);
      
      // Access to the first _basic_ field will cause a load from
      // the parent table but won't load lazy collections like children.
      System.out.println("parent name: "+parent.getName());
      session.close();

      // This should still fail because we didn't access the
      // lazy collection during the session
      try {
         parent.getChildren().size();
         fail("Lazy initialzation exception expected");
      } catch (LazyInitializationException e) {
      }

      // ---------------------
      
      session = HibernateUtil.getSession();
      parent = (Parent)session.load(Parent.class, id);
      
      // Accessing the children will generate SQL to
      // lazily fetch from the child table.
      System.out.println("number of children: "+parent.getChildren().size());
      session.close();

   }

   private Long createData() {
      Session session = HibernateUtil.getSession();
      session.beginTransaction();
      
      Map<String, Child> children = new HashMap<String, Child>();
      Child c1 = new Child();
      c1.setChildName("c1");
      children.put("c1", c1);
      Child c2 = new Child();
      c2.setChildName("c2");
      children.put("c2", c2);
      Child c3 = new Child();
      c3.setChildName("c3");
      children.put("c3", c3);

      Parent parent = new Parent();
      parent.setName("parent name");
      parent.setChildren(children);
      
      Long id = (Long)session.save(parent);
      
      session.getTransaction().commit();
      session.close();
      
      return id;
   }
}