Hibernate学习之单向多对一映射

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一个customer对应多个order。在order中有一个customer的引用。

Customer类的java代码

package com.mamh.hibernate.demo.entities;public class Customer {    private Integer customerId;    private String customerName;    public Customer() {    }    public Customer(String name) {        this.customerName = name;    }    public Integer getCustomerId() {        return customerId;    }    public void setCustomerId(Integer customerId) {        this.customerId = customerId;    }    public String getCustomerName() {        return customerName;    }    public void setCustomerName(String customerName) {        this.customerName = customerName;    }}

Order类的java代码

package com.mamh.hibernate.demo.entities;public class Order {    private Integer orderId;    private String orderName;    private Customer customer;    public Integer getOrderId() {        return orderId;    }    public void setOrderId(Integer orderId) {        this.orderId = orderId;    }    public String getOrderName() {        return orderName;    }    public void setOrderName(String orderName) {        this.orderName = orderName;    }    public Customer getCustomer() {        return customer;    }    public void setCustomer(Customer customer) {        this.customer = customer;    }}

Order类的映射文件，

<hibernate-mapping package="com.mamh.hibernate.demo.entities">    <class name="Order" table="hb_order" schema="mage">        <id name="orderId">            <column name="hb_order_id" sql-type="int(11)"/>            <generator class="native"/>        </id>        <property name="orderName" type="string">            <column name="hb_order_name"/>        </property>        <!-- 映射多对一的关联关系 property不再试用这个多对一的关系了               name是多这一端关联的那个一那一端属性名称               class的类全名               column是多的一端这边数据表的一个列名，一般是外键        -->        <many-to-one name="customer" class="Customer" column="customer_id"/>    </class></hibernate-mapping>

Customer类的映射文件

<hibernate-mapping>    <class name="com.mamh.hibernate.demo.entities.Customer" table="hb_customer" schema="mage">        <id name="customerId">            <column name="hb_customer_id" sql-type="int(11)"/>            <generator class="native"/>        </id>        <property name="customerName" type="string">            <column name="hb_customer_name"/>        </property>    </class></hibernate-mapping>

1.测试保存order和customer的方法

先保存customer，然后保存order。

    @Test    public void testManyToOneSave(){        Customer customer = new Customer("aa");        Order order1 = new Order();        order1.setOrderName("order 1");        Order order2 = new Order();        order2.setOrderName("order 2");        order1.setCustomer(customer);        order2.setCustomer(customer);        //执行save操作        //先保存customer，然后保存order。        session.save(customer);        session.save(order1);        session.save(order2);    }

先保存customer，然后保存order，这个会出现3条插入sql语句。这个是建议这样的顺序的。

Hibernate:     insert     into        mage.hb_customer        (hb_customer_name)     values        (?)Hibernate:     insert     into        mage.hb_order        (hb_order_name, customer_id)     values        (?, ?)Hibernate:     insert     into        mage.hb_order        (hb_order_name, customer_id)     values        (?, ?)

如果是先保存order，然后再保存customer，情况由如何呢？

//执行save操作//先保存order，然后保存customer。session.save(order1);session.save(order2);session.save(customer);

如果是先保存order，然后再保存customer，能成功的。会出现3条insert语句，最后还有2条update语句。
这中情况就多了2条update语句。因为order表需要一个外键，先保存oder的是还不知道这个外键
customer是多少。后来保存好了customer，就知道customer ID了。最后会更新一些oder中的外键。
这样就多了2条update更新语句。这样多了2条语句效率就会低一些。

Hibernate:     insert     into        mage.hb_order        (hb_order_name, customer_id)     values        (?, ?)Hibernate:     insert     into        mage.hb_order        (hb_order_name, customer_id)     values        (?, ?)Hibernate:     insert     into        mage.hb_customer        (hb_customer_name)     values        (?)=destroy=Hibernate:     update        mage.hb_order     set        hb_order_name=?,        customer_id=?     where        hb_order_id=?Hibernate:     update        mage.hb_order     set        hb_order_name=?,        customer_id=?     where        hb_order_id=?

2.测试查询order和customer的方法

查询多的一端的一个对象，默认情况下，只查询了多的一端的对象，而没有查询关联的那一端的对象。
就是说查询Order对象，只得到了Order对象，而没有得到Customer对象。

    @Test    public void testManyToOneGet(){        Order order = (Order) session.get(Order.class, 1);        System.out.println(order.getOrderName() + ":  "+order.getOrderId());        //这里值用到了order对象的属性，没有用的customer的属性，所以不会发送取查询customer相关的sql语句的。    }

Hibernate: //通过这个hibernate的sql输出我们看到没有去查询customer相关的。    select        order0_.hb_order_id as hb1_3_0_,        order0_.hb_order_name as hb2_3_0_,        order0_.customer_id as customer3_3_0_     from        mage.hb_order order0_     where        order0_.hb_order_id=?order 1:  1

如果我们用到了customer的相关属性，例如获取order中的customer对象，
或者直接打印order对象都是会发送查询customer表的sql语句的。

    @Test    public void testManyToOneGet(){        Order order = (Order) session.get(Order.class, 1);        System.out.println(order);        Customer customer = order.getCustomer();        System.out.println(customer);    }

Hibernate:     select        order0_.hb_order_id as hb1_3_0_,        order0_.hb_order_name as hb2_3_0_,        order0_.customer_id as customer3_3_0_     from        mage.hb_order order0_     where        order0_.hb_order_id=?Hibernate:     select        customer0_.hb_customer_id as hb1_2_0_,        customer0_.hb_customer_name as hb2_2_0_     from        mage.hb_customer customer0_     where        customer0_.hb_customer_id=?System.out.println(order);的输出结果：      Order{    orderId=1,     orderName='order 1',     customer=Customer{        customerId=1,         customerName='aa'        }}System.out.println(customer);的输出结果：Customer{    customerId=1,     customerName='aa'}

如果在查询customer对象的时候，有多的一端导航到一的一端时，若此时session被关闭，则
会发生一个LazyInitializationException异常

    @Test    public void testManyToOneGet(){        Order order = (Order) session.get(Order.class, 1);        System.out.println(order.getOrderName() + ":  "+order.getOrderId());        session.close();        Customer customer = order.getCustomer();        System.out.println(customer);    }

Hibernate:     select        order0_.hb_order_id as hb1_3_0_,        order0_.hb_order_name as hb2_3_0_,        order0_.customer_id as customer3_3_0_     from        mage.hb_order order0_     where        order0_.hb_order_id=?order 1:  1=destroy=org.hibernate.LazyInitializationException: could not initialize proxy - no Session    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:149)    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:195)    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)    at com.mamh.hibernate.demo.entities.Customer_$$_javassist_1.toString(Customer_$$_javassist_1.java)    at java.lang.String.valueOf(String.java:2994)    at java.io.PrintStream.println(PrintStream.java:821)    at com.mamh.hibernate.demo.HibernateTest.testManyToOneGet(HibernateTest.java:61)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

获取order对象时，默认情况下，其关联的customer对象是一个代理对象！

3.测试更新order，customer对象

    @Test    public void testManyToOneUpdate() {        Order order = (Order) session.get(Order.class, 1);        order.getCustomer().setCustomerName("new customer name");    }

Hibernate:     select        order0_.hb_order_id as hb1_3_0_,        order0_.hb_order_name as hb2_3_0_,        order0_.customer_id as customer3_3_0_     from        mage.hb_order order0_     where        order0_.hb_order_id=?Hibernate:     select        customer0_.hb_customer_id as hb1_2_0_,        customer0_.hb_customer_name as hb2_2_0_     from        mage.hb_customer customer0_     where        customer0_.hb_customer_id=?=destroy=Hibernate:     update        mage.hb_customer     set        hb_customer_name=?     where        hb_customer_id=?

4.测试删除order和customer

在不设定级联关系的情况下，且1这一端对象有n的对象在引用，不能直接删除。
也就是说customer 的id有在order中作为外键就不能删除这个customer。
要删除也是先把order中的删除完，然后在删除customer中的。

    @Test    public void testManyToOneDelete() {        Customer customer = (Customer) session.get(Customer.class, 1);        session.delete(customer);    }

Hibernate:     select        customer0_.hb_customer_id as hb1_2_0_,        customer0_.hb_customer_name as hb2_2_0_     from        mage.hb_customer customer0_     where        customer0_.hb_customer_id=?=destroy=Nov 17, 2017 2:51:23 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptionsWARN: SQL Error: 1451, SQLState: 23000Hibernate:     delete     from        mage.hb_customer     where        hb_customer_id=?Nov 17, 2017 2:51:23 PM org.hibernate.engine.jdbc.spi.SqlExceptionHelper logExceptionsERROR: Cannot delete or update a parent row: a foreign key constraint fails (`mage`.`hb_order`, CONSTRAINT `FK1C0AD3C966B2F7AA` FOREIGN KEY (`customer_id`) REFERENCES `hb_customer` (`hb_customer_id`))Nov 17, 2017 2:51:23 PM org.hibernate.engine.jdbc.batch.internal.BatchingBatch performExecutionERROR: HHH000315: Exception executing batch [Cannot delete or update a parent row: a foreign key constraint fails (`mage`.`hb_order`, CONSTRAINT `FK1C0AD3C966B2F7AA` FOREIGN KEY (`customer_id`) REFERENCES `hb_customer` (`hb_customer_id`))]org.hibernate.exception.ConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`mage`.`hb_order`, CONSTRAINT `FK1C0AD3C966B2F7AA` FOREIGN KEY (`customer_id`) REFERENCES `hb_customer` (`hb_customer_id`))    at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:128)    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)    at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:129)    at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81)    at com.sun.proxy.$Proxy9.executeBatch(Unknown Source)    at org.hibernate.engine.jdbc.batch.internal.BatchingBatch.performExecution(BatchingBatch.java:110)    at org.hibernate.engine.jdbc.batch.internal.BatchingBatch.doExecuteBatch(BatchingBatch.java:101)    at org.hibernate.engine.jdbc.batch.internal.AbstractBatchImpl.execute(AbstractBatchImpl.java:161)    at org.hibernate.engine.jdbc.internal.JdbcCoordinatorImpl.executeBatch(JdbcCoordinatorImpl.java:162)    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:357)    at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:280)    at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:326)    at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:52)    at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1127)    at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:325)    at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)    at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)    at com.mamh.hibernate.demo.HibernateTest.destroy(HibernateTest.java:315)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:33)    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)    at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)Caused by: java.sql.BatchUpdateException: Cannot delete or update a parent row: a foreign key constraint fails (`mage`.`hb_order`, CONSTRAINT `FK1C0AD3C966B2F7AA` FOREIGN KEY (`customer_id`) REFERENCES `hb_customer` (`hb_customer_id`))    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)    at com.mysql.cj.core.util.Util.handleNewInstance(Util.java:185)    at com.mysql.cj.core.util.Util.getInstance(Util.java:168)    at com.mysql.cj.core.util.Util.getInstance(Util.java:175)    at com.mysql.cj.jdbc.exceptions.SQLError.createBatchUpdateException(SQLError.java:636)    at com.mysql.cj.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1734)    at com.mysql.cj.jdbc.PreparedStatement.executeBatchInternal(PreparedStatement.java:1217)    at com.mysql.cj.jdbc.StatementImpl.executeBatch(StatementImpl.java:1009)    at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeBatch(NewProxyPreparedStatement.java:1723)    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    at java.lang.reflect.Method.invoke(Method.java:498)    at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:122)    ... 37 moreCaused by: java.sql.SQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails (`mage`.`hb_order`, CONSTRAINT `FK1C0AD3C966B2F7AA` FOREIGN KEY (`customer_id`) REFERENCES `hb_customer` (`hb_customer_id`))    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:533)    at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:513)    at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:115)    at com.mysql.cj.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:1983)    at com.mysql.cj.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1826)    at com.mysql.cj.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2034)    at com.mysql.cj.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1712)    ... 45 moreProcess finished with exit code 255

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