Hibernate写实体映射方法

ゝ一世哀愁。 2022-06-14 06:21 220阅读 0赞

**Hibernate写实体映射方法**

## 前言： ##

在用SSH的框架时，有了实体，可以通过写Hibernate的映射完成自动的建立数据表，今天小编就来总结一下怎么建立hbm.xml的映射表的技巧：

## 画UML图，根据UML写实体 ##

实体设计和映射：

![Center][]

其实上面的所有实体和实体关系都可以用 Rose 或EA自动生成的：

根据EA图看出实体之间关系，在Hibernate中怎么设计呢？ Role，User，Department

**步骤：第一步写注释，第二步代码模板，第三步填充代码**

模板如下：

![Center 1][]

注意：多对一是，外键在多的一方

<many-to-one name="parent" class="Department" column="parentId"></many-to-one>

** **

**外键总结：**

外键引用的那个列在主表中必须是主键列或者唯一列。  
   1：n的肯定把外键建立在n的那张表上。  
   1：1，一般要看谁是主表，谁是附属表，外键当然建立在附属表中。  
   n：m的情况，需要建立一个关系表，两个原表和其关系分别是1：n，1：m

![Center 2][]

## 写 映 射 ##

## 表与表关系总结： ##

下面是关系的模板:**什么的属性，本类与？的怎样的关系**

说明：（1）什么，都是与本类关系的表或关系而非自己；

（2）？都是指其他类

（3）name=”什么” class=”？” column=”什么+Id”

### （1）什么的属性，本类与？的一对多 ###

注意，关系为一对多是，这里的column值是一即本类的主键；如果是多对一，这column的值是什么+Id.

<one-to-many class=”？”/>

</set>

例如：

<set name="topics"> <key column="forumId"></key> <one-to-many class="Topic"/> </set>

### （2）什么的属性，本类与？的多对一 ###

<many-to-one name=”什么” column=”什么\+Id” class=”?”>

</many-to-one>这里的column值就是什么\+Id,column也即是外键值。

例如：

<many-to-one name="forum" class="Forum"column="forumId"></many-to-one>

### （3）什么的属性，本类与？的多对多 ###

<many-to-manyclass=”？” colum=”？\+Id”/>

</set>

例如：

<setname="users" table="itcast_user_role"> <keycolumn="roleId"></key> <many-to-many class="User"column="userId"></many-to-many> </set>

<setname="privileges" table="itcast_role_privilege"lazy="false"> <keycolumn="roleId"></key> <many-to-manyclass="Privilege" column="privilegeId"></many-to-many> </set>

### （4）什么的属性，本类与？的一对一，采用基于外键的一对一映射方式，本方有外键。 ###

**<many-to-one name=”什么”   column=”什么\+Id”   class=”?”   unique=”true”></many-to-one>**

例如：

<many-to-onename="lastTopic" class="Topic"column="lastTopicId" unique="true"></many-to-one>

<many-to-onename="lastReply" class="Reply"column="lastReplyId" unique="true"></many-to-one>

## 注意： ##

（1），一对一的关系，比如只要在一个实体中说明就行了，下面三个个实体，只在Forum和Topic中写一对一的关系，具体的在上面两个例子。

![Center 3][]

（2）关于继承的，例如下面Topic和Reply 都继承Article，Article不用谢实体表，但是和User的关系都是多对一，在Topic和Reply中都要注明这个关系。

![Center 4][]

<many-to-one name="forum"class="Forum" column="forumId"></many-to-one>

## 将映射放到hibernate.cfg.xml中 ##

![Center 5][]

建表测试报错：

org.springframework.beans.factory.BeanCreationException:Error creating bean with name 'departmentDaoImpl': Injection of resource fieldsfailed; nested exception is org.springframework.beans.factory.BeanCreationException:Error creating bean with name 'sessionFactory' defined in class path resource\[applicationContext.xml\]: Invocation of init method failed; nested exception isorg.hibernate.HibernateException: Unable to instantiate default tuplizer\[org.hibernate.tuple.entity.PojoEntityTuplizer\]

atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessAfterInstantiation(CommonAnnotationBeanPostProcessor.java:292)

at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:959)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)

atjava.security.AccessController.doPrivileged(Native Method)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)

atorg.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)

atorg.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)

at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)

atorg.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)

atorg.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429)

atorg.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)

atorg.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380)

atorg.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)

atorg.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)

atcn.itcast.oa.test.SpringTest.<init>(SpringTest.java:10)

atsun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

atsun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)

atsun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

atjava.lang.reflect.Constructor.newInstance(Constructor.java:525)

atorg.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:195)

atorg.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:244)

atorg.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)

atorg.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:241)

atorg.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)

atorg.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)

atorg.junit.runners.ParentRunner$3.run(ParentRunner.java:238)

atorg.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)

atorg.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)

atorg.junit.runners.ParentRunner.access$000(ParentRunner.java:53)

atorg.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)

atorg.junit.runners.ParentRunner.run(ParentRunner.java:309)

atorg.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)

atorg.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)

atorg.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)

atorg.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)

atorg.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)

atorg.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Causedby: org.springframework.beans.factory.BeanCreationException: Error creatingbean with name 'sessionFactory' defined in class path resource\[applicationContext.xml\]: Invocation of init method failed; nested exception isorg.hibernate.HibernateException: Unable to instantiate default tuplizer\[org.hibernate.tuple.entity.PojoEntityTuplizer\]

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1338)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:473)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)

atjava.security.AccessController.doPrivileged(Native Method)

at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)

atorg.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)

at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)

atorg.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)

at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)

atorg.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:168)

atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:435)

atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:409)

atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:537)

atorg.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:180)

atorg.springframework.beans.factory.annotation.InjectionMetadata.injectFields(InjectionMetadata.java:105)

atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessAfterInstantiation(CommonAnnotationBeanPostProcessor.java:289)

... 38 more

Causedby: org.hibernate.HibernateException: Unable to instantiate default tuplizer\[org.hibernate.tuple.entity.PojoEntityTuplizer\]

atorg.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:108)

atorg.hibernate.tuple.entity.EntityTuplizerFactory.constructDefaultTuplizer(EntityTuplizerFactory.java:133)

atorg.hibernate.tuple.entity.EntityEntityModeToTuplizerMapping.<init>(EntityEntityModeToTuplizerMapping.java:80)

atorg.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:322)

atorg.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:473)

atorg.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:133)

atorg.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:84)

atorg.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:284)

atorg.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1842)

atorg.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory(LocalSessionFactoryBean.java:814)

atorg.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:732)

atorg.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:211)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1369)

atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1335)

... 53 more

Causedby: java.lang.reflect.InvocationTargetException

atsun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

atsun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)

atsun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)

atjava.lang.reflect.Constructor.newInstance(Constructor.java:525)

at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:105)

... 66 more

Causedby: org.hibernate.PropertyNotFoundException: Could not find a getter forlastUpdate in class cn.itcast.oa.domain.Topic

atorg.hibernate.property.BasicPropertyAccessor.createGetter(BasicPropertyAccessor.java:326)

atorg.hibernate.property.BasicPropertyAccessor.getGetter(BasicPropertyAccessor.java:320)

atorg.hibernate.mapping.Property.getGetter(Property.java:304)

atorg.hibernate.tuple.entity.PojoEntityTuplizer.buildPropertyGetter(PojoEntityTuplizer.java:297)

atorg.hibernate.tuple.entity.AbstractEntityTuplizer.<init>(AbstractEntityTuplizer.java:155)

atorg.hibernate.tuple.entity.PojoEntityTuplizer.<init>(PojoEntityTuplizer.java:77)

... 71 more

调错结果：其实就是一个字段没有写对：lastUpdateTime写成lastUpdatetime

## 小结： ##

学习了，实践了，今天对这个进行一个比较全面的总结。

表与表之间的关系就是那么几种，一对多，一对一，多对一，多对多。画好UML图，更加UML图自动生成实体之后在写hbm.xml映射时，按照模板一步一步照着填空就行了：

下面是关系的模板:**什么的属性，本类与？的怎样的关系**

说明：（1）什么，都是与本类关系的表或关系而非自己；

（2）？都是指其他类

（3）name=”什么” class=”？” column=”什么+Id”

[Center]: /images/20220614/c91d2e0ce7234738b646e203b14372ee.png
[Center 1]: /images/20220614/82ce9f55862849acba460611b34cb201.png
[Center 2]: /images/20220614/a57d1a8bb8534ec38529cc293a4a39b0.png
[Center 3]: /images/20220614/7506495297e44ea695c8e0525ea4547c.png
[Center 4]: /images/20220614/9b74813a561d45e49d0b5cdc0e11e73c.png
[Center 5]: /images/20220614/1177fa4d3278445eb0ee003e473d4a1f.png