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();
        }
    }

}