hibernate学习4-关联映射-多对一

关联映射分类

一对一，一对多（多对一），多对多

单向关联和双向关联

单向关联多对一

客户和订单

数据表：

customer(id,name,email)

order(id,name,orderNumber,customerId(外键))

类

Customer(Integerid,Stringname,Stringemail)

Order(Integerid,Stringname,StringorderNumber,Customercustomer)//不是customerId

映射文件customer.hbm.xml

<?xmlversion="1.0"encoding="UTF-8"?>

<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<classname="com.limf.bean.Customer"table="Customer">

<idname="id"column="id">

<generatorclass="native"></generator>

</id>

<propertyname="name"column="name"></property>

<propertyname="emai"column="email"></property>

</class>

</hibernate-mapping>

映射文件order.hbm.xml

<?xmlversion="1.0"encoding="UTF-8"?>

<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<classname="com.limf.bean.Order"table="Order">

<idname="id"column="id">

<generatorclass="native"></generator>

</id>

<propertyname="name"column="name"></property>

<propertyname="orderNumber"column="orderNumber"></property>

<many-to-onename="customer"class="com.limf.bean.Customer">

<columnname="customerId"></column>

</many-to-one>

</class>

</hibernate-mapping>

保存订单时需要先从数据库加载一个customer，调用order.setCustomer(Customerc)

当加载一个订单时，session.get(Order.class,orderId),得到order

再取得customer,order.getCustomer(),会报错

需要对Customer设置延迟加载false

修改customer.hbm.xml

<classname="com.limf.bean.Customer"table="Customer"lazy="false">

双向关联多对一

Customer类中增多一个属性Setorders=newHashSet()

映射文件customer.hbm.xml

<?xmlversion="1.0"encoding="UTF-8"?>

<!DOCTYPEhibernate-mappingPUBLIC"-//Hibernate/HibernateMappingDTD3.0//EN""http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

<classname="com.limf.bean.Customer"table="Customer">

<idname="id"column="id">

<generatorclass="native"></generator>

</id>

<propertyname="name"column="name"></property>

<propertyname="emai"column="email"></property>

<setname="orders"lazy="false"><!--不要延迟加载-->

<keycolumn="CustomerId"/><!--集合外键-->

<one-to-manyclass="com.limf.bean.Order"/>

</set>

</class>

</hibernate-mapping>