JavaPersistenceWithHibernate第二版笔记-第七章-002Mapping an identifier bag(@CollectionId、@ElementCollection、@CollectionTable、@Type)

一、结构

A bag is an unordered collection that allows duplicate elements, like the java.util.Collection interface. Curiously, the Java Collections framework doesn’t include a bag implementation. You initialize the property with an ArrayList , and
Hibernate ignores the index of elements when storing and loading elements.

二、代码

1.

 package org.jpwh.model.collections.bagofstrings;

 import org.jpwh.model.Constants;

 import javax.persistence.CollectionTable;
 import javax.persistence.Column;
 import javax.persistence.ElementCollection;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import java.util.ArrayList;
 import java.util.Collection;

 @Entity
 public class Item {

     @Id
     @GeneratedValue(generator = Constants.ID_GENERATOR)
     protected Long id;

     @ElementCollection
     @CollectionTable(name = "IMAGE")
     @Column(name = "FILENAME")
     @org.hibernate.annotations.CollectionId( // Surrogate PK allows duplicates!
             columns = @Column(name = "IMAGE_ID"),
             type = @org.hibernate.annotations.Type(type = "long"),
             generator = Constants.ID_GENERATOR)
     protected Collection<String> images = new ArrayList<String>(); // No BagImpl in JDK!

     public Long getId() {
         return id;
     }

     public Collection<String> getImages() {
         return images;
     }

     public void setImages(Collection<String> images) {
         this.images = images;
     }

     // ...
 }

2.

 package org.jpwh.test.collections;

 import org.jpwh.env.JPATest;
 import org.jpwh.model.collections.bagofstrings.Item;
 import org.testng.annotations.BeforeClass;
 import org.testng.annotations.Test;

 import javax.persistence.EntityManager;
 import javax.transaction.UserTransaction;

 import static org.testng.Assert.assertEquals;

 public class BagOfStrings extends JPATest {

     @Override
     public void configurePersistenceUnit() throws Exception {
         configurePersistenceUnit("BagOfStringsPU");
     }

     @Test
     public void storeLoadCollection() throws Exception {
         UserTransaction tx = TM.getUserTransaction();
         try {
             tx.begin();
             EntityManager em = JPA.createEntityManager();
             Item someItem = new Item();

             someItem.getImages().add("foo.jpg");
             someItem.getImages().add("bar.jpg");
             someItem.getImages().add("baz.jpg");
             someItem.getImages().add("baz.jpg");

             em.persist(someItem);
             tx.commit();
             em.close();
             Long ITEM_ID = someItem.getId();

             tx.begin();
             em = JPA.createEntityManager();
             Item item = em.find(Item.class, ITEM_ID);
             assertEquals(item.getImages().size(), 4);
             tx.commit();
             em.close();
         } finally {
             TM.rollback();
         }
     }

 }

3.

 <persistence-unit name="BagOfStringsPU">
         <jta-data-source>myDS</jta-data-source>
         <class>org.jpwh.model</class>
         <class>org.jpwh.model.collections.bagofstrings.Item</class>
         <exclude-unlisted-classes>true</exclude-unlisted-classes>
     </persistence-unit>

4.

 package org.jpwh.test.collections;

 import org.jpwh.env.JPATest;
 import org.jpwh.model.collections.bagofstrings.Item;
 import org.testng.annotations.BeforeClass;
 import org.testng.annotations.Test;

 import javax.persistence.EntityManager;
 import javax.transaction.UserTransaction;

 import static org.testng.Assert.assertEquals;

 public class BagOfStrings extends JPATest {

     @Override
     public void configurePersistenceUnit() throws Exception {
         configurePersistenceUnit("BagOfStringsPU");
     }

     @Test
     public void storeLoadCollection() throws Exception {
         UserTransaction tx = TM.getUserTransaction();
         try {
             tx.begin();
             EntityManager em = JPA.createEntityManager();
             Item someItem = new Item();

             someItem.getImages().add("foo.jpg");
             someItem.getImages().add("bar.jpg");
             someItem.getImages().add("baz.jpg");
             someItem.getImages().add("baz.jpg");

             em.persist(someItem);
             tx.commit();
             em.close();
             Long ITEM_ID = someItem.getId();

             tx.begin();
             em = JPA.createEntityManager();
             Item item = em.find(Item.class, ITEM_ID);
             assertEquals(item.getImages().size(), 4);
             tx.commit();
             em.close();
         } finally {
             TM.rollback();
         }
     }

 }