一、结构
二、代码
1.
package org.jpwh.model.collections.setofstrings; 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.JoinColumn;
import java.util.HashSet;
import java.util.Set; @Entity
public class Item { @Id
@GeneratedValue(generator = Constants.ID_GENERATOR)
protected Long id; @ElementCollection
@CollectionTable(
name = "IMAGE", // Defaults to ITEM_IMAGES
joinColumns = @JoinColumn(name = "ITEM_ID")) // Default, actually
@Column(name = "FILENAME") // Defaults to IMAGES
protected Set<String> images = new HashSet<String>(); // Initialize field here public Long getId() {
return id;
} public Set<String> getImages() {
return images;
} public void setImages(Set<String> images) {
this.images = images;
} // ...
}
2.
package org.jpwh.test.collections; import org.jpwh.env.JPATest;
import org.jpwh.model.collections.setofstrings.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 SetOfStrings extends JPATest { @Override
public void configurePersistenceUnit() throws Exception {
configurePersistenceUnit("SetOfStringsPU");
} @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"); // Duplicate, filtered at Java level by HashSet! 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(), 3);
tx.commit();
em.close();
} finally {
TM.rollback();
}
} }
It doesn’t seem likely that you’d allow the user to attach the same image more than once to the same item,
