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();
        }
    }

}