初学Hibernate,让人抓狂

Hibernate是个强大,开发效率高的开源框架—这已是行业所公认的事实.

对于初接触Hibernate的我来说,却因为他强大的封装能力,出现问题时,完成不知从何处下手.

信手写了个Person类:

package com.wls.domain;

 

import java.util.Date;

 

public class Person {

    private Integer personId;

    private String name;

    private Date birthday;

    private Address address;

   

    public Person(){

       

    }

 

    public Integer getPersonId() {

        return personId;

    }

 

    public void setPersonId(Integer personId) {

        this.personId = personId;

    }

 

    public String getName() {

        return name;

    }

 

    public void setName(String name) {

        this.name = name;

    }

 

    public Date getBirthday() {

        return birthday;

    }

 

    public void setBirthday(Date birthday) {

        this.birthday = birthday;

    }

 

    public Address getAddress() {

        return address;

    }

 

    public void setAddress(Address address) {

        this.address = address;

    }

 

    @Override

    public String toString() {

        return "Person [personId=" + personId + ", name=" + name

                + ", birthday=" + birthday + ", address=" + address + "]";

    }

   

   

}

再写一个Address类:

package com.wls.domain;

 

import java.util.Date;

 

public class Address {

    private Integer addressId;

    private String addressDetail;

   

    private Person person;

   

   

    public Address(){

       

    }

   

    public Address(String addressDetail){

        this.addressDetail=addressDetail;

    }

 

    public Integer getAddressId() {

        return addressId;

    }

 

    public void setAddressId(Integer addressId) {

        this.addressId = addressId;

    }

 

    public String getAddressDetail() {

        return addressDetail;

    }

 

    public void setAddressDetail(String addressDetail) {

        this.addressDetail = addressDetail;

    }

 

    public Person getPerson() {

        return person;

    }

 

    public void setPerson(Person person) {

        this.person = person;

    }

 

    @Override

    public String toString() {

        return "Address [addressId=" + addressId + ", addressDetail="

                + addressDetail +"]";

    }

}

这个两Pojo对应的映射文件为:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE hibernate-mapping PUBLIC

        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"

        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">

 

<hibernate-mapping package="com.wls.domain">

    <class name="Person">

        <id name="personId" type="java.lang.Integer">

            <generator class="native"></generator>

        </id>

        <property name="name" type="java.lang.String"></property>

        <property name="birthday" type="java.util.Date"></property>

        <one-to-one name="address" class="Address" property-ref="addressId" cascade="save-update" >

        </one-to-one>

    </class>

   

    <class name="Address">

        <id name="addressId" type="java.lang.Integer">

            <generator class="native"></generator>

        </id>

        <property name="addressDetail" type="java.lang.String"></property>

        <many-to-one name="person" class="Person"  unique="true" not-null="true"></many-to-one>

    </class>

</hibernate-mapping>

前奏写好了,之后写了个DAO--UserManagerDao:

package com.wls.dao;

 

import java.util.ArrayList;

import java.util.List;

 

import org.hibernate.Query;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.Transaction;

 

import com.wls.domain.Address;

import com.wls.domain.Person;

 

public class UserManagerDao {

    private SessionFactory sessionFactory;

    private Session session;

   

   

    public void setSessionFactory(SessionFactory sessionFactory) {

        this.sessionFactory = sessionFactory;

    }

    public Session getSession() {

       

        if(session==null){

            session=sessionFactory.openSession();

        }

        return session;

    }

   

    public Integer addAddress(Address address){

        Transaction tx=getSession().beginTransaction();

        Integer AddressId=(Integer)getSession().save(address);

        tx.commit();

        return AddressId;

    }

   

    public Integer addPerson(Person person){

        Transaction tx=getSession().beginTransaction();

        Integer personId=(Integer)getSession().save(person);

        tx.commit();

        return personId;

    }

   

    public Person getPerson(Integer personId){

        Transaction tx=getSession().beginTransaction();

        Person person=(Person) getSession().get(Person.class, personId);

        tx.commit();

        return person;

    }

   

    public List<Person> getAllPerons(){

        Transaction tx=getSession().beginTransaction();

        Query query=getSession().createQuery("select person from Person person");

        if(query==null){

            System.out.println("query is null");

            return new ArrayList<Person>();

        }else{

            System.out.println("query is not null");

        }

        List<Person> persons=query.list();

        tx.commit();

        return persons;

    }

   

    public List<Address> getAllAddresses(){

        Transaction tx=getSession().beginTransaction();

        Query query=getSession().createQuery("select person from Address person");

        if(query==null){

            System.out.println("query is null");

            return new ArrayList<Address>();

        }else{

            System.out.println("query is not null");

        }

        List<Address> addresses=query.list();

        tx.commit();

        return addresses;

    }

   

   

}

 

最后,就只差用于测试的类了—MainTest:

package com.wls.test;

 

import java.util.Date;

import java.util.List;

 

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

 

import com.wls.dao.UserManagerDao;

import com.wls.domain.Address;

import com.wls.domain.Person;

 

public class MainTest {

    public static void main(String[] args){

        System.out.println("Main Method!");

       

        ApplicationContext context=new ClassPathXmlApplicationContext("SpringConfig.xml");

        UserManagerDao userManagerDao=context.getBean("userManagerDao", UserManagerDao.class);

       

        Address address=new Address("广东广州");

       

        Person person=new Person();

       

        person.setBirthday(new Date());

        person.setName("佢顺");

       

        address.setPerson(person);

       

        userManagerDao.addAddress(address);

        System.out.println("Main Mehtod End!");

    }

}

随手点了下运行按钮,却出现了如下错误:

Hibernate: select hibernate_sequence.nextval from dual

Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.wls.domain.Person

    at org.hibernate.engine.ForeignKeys.getEntityIdentifierIfNotUnsaved(ForeignKeys.java:243)

    at org.hibernate.type.EntityType.getIdentifier(EntityType.java:456)

    at org.hibernate.type.ManyToOneType.isDirty(ManyToOneType.java:265)

    at org.hibernate.type.ManyToOneType.isDirty(ManyToOneType.java:275)

    at org.hibernate.type.TypeHelper.findDirty(TypeHelper.java:295)

    at org.hibernate.persister.entity.AbstractEntityPersister.findDirty(AbstractEntityPersister.java:3403)

    at org.hibernate.event.def.DefaultFlushEntityEventListener.dirtyCheck(DefaultFlushEntityEventListener.java:520)

    at org.hibernate.event.def.DefaultFlushEntityEventListener.isUpdateNecessary(DefaultFlushEntityEventListener.java:230)

    at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:154)

    at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:219)

    at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)

    at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)

    at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1216)

    at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:383)

    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:133)

    at com.wls.dao.UserManagerDao.addAddress(UserManagerDao.java:33)

    at com.wls.test.MainTest.main(MainTest.java:33)

 

再次确认映射文件,我已经写了cascade=save-update为什么会出现如此问题?

思考了半个小时,头疼,放弃了.

然后改了一下MainTest:

package com.wls.test;

 

import java.util.Date;

import java.util.List;

 

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

 

import com.wls.dao.UserManagerDao;

import com.wls.domain.Address;

import com.wls.domain.Person;

 

public class MainTest {

    public static void main(String[] args){

        System.out.println("Main Method!");

       

        ApplicationContext context=new ClassPathXmlApplicationContext("SpringConfig.xml");

        UserManagerDao userManagerDao=context.getBean("userManagerDao", UserManagerDao.class);

        Address address=new Address("广东广州");

        Person person=new Person();

        person.setBirthday(new Date());

        person.setName("佢顺");

        Integer personId=userManagerDao.addPerson(person);

        address.setPerson(person);

        userManagerDao.addAddress(address);

        List<Address> addresses=userManagerDao.getAllAddresses();

       

        for(Address a:addresses){

            System.out.println(a);

        }

       

        System.out.println("Main Mehtod End!");

    }

}

运行结果如春风吹过,舒畅的感觉:

Hibernate: select hibernate_sequence.nextval from dual

Hibernate: insert into Person (name, birthday, personId) values (?, ?, ?)

Hibernate: select hibernate_sequence.nextval from dual

Hibernate: insert into Address (addressDetail, person, addressId) values (?, ?, ?)

query is not null

Hibernate: select address0_.addressId as addressId1_, address0_.addressDetail as addressD2_1_, address0_.person as person1_ from Address address0_

Address [addressId=42, addressDetail=广东广州]

Address [addressId=44, addressDetail=广东广州]

Address [addressId=46, addressDetail=广东广州]

Address [addressId=48, addressDetail=广东广州]

Address [addressId=50, addressDetail=广东广州]

Address [addressId=52, addressDetail=广东广州]

Address [addressId=55, addressDetail=广东广州]

Main Mehtod End!

 

 

再改MainTest:

package com.wls.test;

 

import java.util.Date;

import java.util.List;

 

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

 

import com.wls.dao.UserManagerDao;

import com.wls.domain.Address;

import com.wls.domain.Person;

 

public class MainTest {

    public static void main(String[] args){

        System.out.println("Main Method!");

       

        ApplicationContext context=new ClassPathXmlApplicationContext("SpringConfig.xml");

        UserManagerDao userManagerDao=context.getBean("userManagerDao", UserManagerDao.class);

       

        Address address=new Address("广东广州");

       

        Person person=new Person();

       

        person.setBirthday(new Date());

        person.setName("佢顺");

       

        Integer personId=userManagerDao.addPerson(person);

        address.setPerson(person);

       

        userManagerDao.addAddress(address);

   

        List<Person> persons=userManagerDao.getAllPerons();

       

        for(Person p:persons){

            System.out.println(p);

        }

       

        System.out.println("Main Mehtod End!");

    }

}

 

想不到冬天来得这么快:

Exception in thread "main" java.lang.NullPointerException

    at org.hibernate.persister.entity.AbstractEntityPersister.loadByUniqueKey(AbstractEntityPersister.java:1791)

    at org.hibernate.type.EntityType.loadByUniqueKey(EntityType.java:681)

    at org.hibernate.type.EntityType.resolve(EntityType.java:441)

    at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:139)

    at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:982)

    at org.hibernate.loader.Loader.doQuery(Loader.java:857)

    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)

    at org.hibernate.loader.Loader.doList(Loader.java:2533)

    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)

    at org.hibernate.loader.Loader.list(Loader.java:2271)

    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:452)

    at org.hibernate.hql.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:363)

    at org.hibernate.engine.query.HQLQueryPlan.performList(HQLQueryPlan.java:196)

    at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1268)

    at org.hibernate.impl.QueryImpl.list(QueryImpl.java:102)

    at com.wls.dao.UserManagerDao.getAllPerons(UserManagerDao.java:60)

    at com.wls.test.MainTest.main(MainTest.java:35)

想了半天,还是不明白为什么是java.lang.NullPointerException想经过测试, com.wls.dao.UserManagerDao.getAllPerons(UserManagerDao.java:60)中的query并不是null.看来问题是出在Peson对象上面了.

那是不是说我不用Address的话永远就取不了Peson了.

解决方案在哪里,又是仰望星空半天.

嗯,解决方案不在今天.