JavaPersistenceWithHibernate第二版笔记-第七章-003Mapping an identifier bag(@OrderColumn、@ElementCollection、@CollectionTable、、)

一、结构

二、代码

1.

 package org.jpwh.model.collections.listofstrings;

 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 javax.persistence.OrderColumn;
 import java.util.ArrayList;
 import java.util.List;

 @Entity
 public class Item {

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

     @ElementCollection
     @CollectionTable(name = "IMAGE")
     @OrderColumn // Enables persistent order, Defaults to IMAGES_ORDER
     @Column(name = "FILENAME")
     protected List<String> images = new ArrayList<String>();

     public Long getId() {
         return id;
     }

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

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

     // ...
 }

2.

 package org.jpwh.test.collections;

 import org.jpwh.env.JPATest;
 import org.jpwh.model.collections.listofstrings.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 ListOfStrings extends JPATest {

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

     @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);
             assertEquals(item.getImages().get(0), "foo.jpg");
             assertEquals(item.getImages().get(1), "bar.jpg");
             assertEquals(item.getImages().get(2), "baz.jpg");
             assertEquals(item.getImages().get(3), "baz.jpg");
             tx.commit();
             em.close();
         } finally {
             TM.rollback();
         }
     }

 }

3.

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

不足之处，无论插入还是删除元素，Hibernate都需要update其他元素的位置