JavaPersistenceWithHibernate第二版笔记-第六章-Mapping inheritance-008Polymorphic many-to-one associations(@ManyToOne、@Inheritance、)

一、结构

二、代码

1.

 package org.jpwh.model.inheritance.associations.manytoone;

 import org.jpwh.model.Constants;

 import javax.persistence.*;
 import javax.validation.constraints.NotNull;

 // Can not be @MappedSuperclass when it's a target class in associations!
 @Entity
 @Inheritance(strategy = InheritanceType.JOINED)
 public abstract class BillingDetails {

     protected Long id;

     @NotNull
     protected String owner;

     protected BillingDetails() {
     }

     protected BillingDetails(String owner) {
         this.owner = owner;
     }

     // Use property instead of field access, so calling getId() doesn't initialize a proxy!
     @Id
     @GeneratedValue(generator = Constants.ID_GENERATOR)
     public Long getId() {
         return id;
     }

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

     public String getOwner() {
         return owner;
     }

     public void setOwner(String owner) {
         this.owner = owner;
     }

     public void pay(int amount) {
         // NOOP
     }
 }

2.

 package org.jpwh.model.inheritance.associations.manytoone;

 import javax.persistence.Entity;
 import javax.validation.constraints.NotNull;

 @Entity
 public class CreditCard extends BillingDetails {

     @NotNull
     protected String cardNumber;

     @NotNull
     protected String expMonth;

     @NotNull
     protected String expYear;

     public CreditCard() {
         super();
     }

     public CreditCard(String owner, String cardNumber, String expMonth, String expYear) {
         super(owner);
         this.cardNumber = cardNumber;
         this.expMonth = expMonth;
         this.expYear = expYear;
     }

     public String getCardNumber() {
         return cardNumber;
     }

     public void setCardNumber(String cardNumber) {
         this.cardNumber = cardNumber;
     }

     public String getExpMonth() {
         return expMonth;
     }

     public void setExpMonth(String expMonth) {
         this.expMonth = expMonth;
     }

     public String getExpYear() {
         return expYear;
     }

     public void setExpYear(String expYear) {
         this.expYear = expYear;
     }

 }

3.

 package org.jpwh.model.inheritance.associations.manytoone;

 import javax.persistence.Entity;
 import javax.validation.constraints.NotNull;

 @Entity
 public class BankAccount extends BillingDetails {

     @NotNull
     protected String account;

     @NotNull
     protected String bankname;

     @NotNull
     protected String swift;

     public BankAccount() {
         super();
     }

     public BankAccount(String owner, String account, String bankname, String swift) {
         super(owner);
         this.account = account;
         this.bankname = bankname;
         this.swift = swift;
     }

     public String getAccount() {
         return account;
     }

     public void setAccount(String account) {
         this.account = account;
     }

     public String getBankname() {
         return bankname;
     }

     public void setBankname(String bankname) {
         this.bankname = bankname;
     }

     public String getSwift() {
         return swift;
     }

     public void setSwift(String swift) {
         this.swift = swift;
     }
 }

4.

 package org.jpwh.model.inheritance.associations.manytoone;

 import org.jpwh.model.Constants;

 import javax.persistence.*;
 import javax.validation.constraints.NotNull;

 @Entity
 @Table(name = "USERS")
 public class User {

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

     @NotNull
     protected String username;

     @ManyToOne(fetch = FetchType.LAZY)
     protected BillingDetails defaultBilling;

     public User() {
     }

     public User(String username) {
         this.username = username;
     }

     public Long getId() {
         return id;
     }

     public String getUsername() {
         return username;
     }

     public void setUsername(String username) {
         this.username = username;
     }

     public BillingDetails getDefaultBilling() {
         return defaultBilling;
     }

     public void setDefaultBilling(BillingDetails defaultBilling) {
         this.defaultBilling = defaultBilling;
     }

     // ...
 }

5.测试

 package org.jpwh.test.inheritance;

 import org.jpwh.env.JPATest;
 import org.jpwh.model.inheritance.associations.manytoone.BillingDetails;
 import org.jpwh.model.inheritance.associations.manytoone.CreditCard;
 import org.jpwh.model.inheritance.associations.manytoone.User;
 import org.testng.annotations.BeforeClass;
 import org.testng.annotations.Test;

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

 import static org.testng.Assert.*;

 public class PolymorphicManyToOne extends JPATest {

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

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

             CreditCard cc = new CreditCard(
                 "John Doe", "1234123412341234", "06", "2015"
             );
             User johndoe = new User("johndoe");
             johndoe.setDefaultBilling(cc);

             em.persist(cc);
             em.persist(johndoe);

             tx.commit();
             em.close();

             Long USER_ID = johndoe.getId();

             tx.begin();
             em = JPA.createEntityManager();
             {
                 User user = em.find(User.class, USER_ID);

                 // Invoke the pay() method on a concrete subclass of BillingDetails
                 user.getDefaultBilling().pay(123);
                 assertEquals(user.getDefaultBilling().getOwner(), "John Doe");
             }

             tx.commit();
             em.close();

             tx.begin();
             em = JPA.createEntityManager();
             {
                 User user = em.find(User.class, USER_ID);

                 BillingDetails bd = user.getDefaultBilling();

                 assertFalse(bd instanceof CreditCard);

                 // Don't do this, ClassCastException!
                 // CreditCard creditCard = (CreditCard) bd;
             }
             {
                 User user = em.find(User.class, USER_ID);

                 //because the  defaultBilling property is
                 // mapped with  FetchType.LAZY , Hibernate will proxy the association target.
                 BillingDetails bd = user.getDefaultBilling();

                 CreditCard creditCard =
                     em.getReference(CreditCard.class, bd.getId()); // No SELECT!

                 assertTrue(bd != creditCard); // Careful!
             }
             tx.commit();
             em.close();

             tx.begin();
             em = JPA.createEntityManager();
             {
                 User user = (User) em.createQuery(
                     "select u from User u " +
                         "left join fetch u.defaultBilling " +
                         "where u.id = :id")
                     .setParameter("id", USER_ID)
                     .getSingleResult();

                 // No proxy has been used, the BillingDetails instance has been fetched eagerly
                 CreditCard creditCard = (CreditCard) user.getDefaultBilling();
             }
             tx.commit();
             em.close();

         } finally {
             TM.rollback();
         }
     }

 }