Hibernate fetch = join

1. TUser与TOrder 一对多关系

xml代码
<class name="TUser" table="t_user" catalog="test">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="native" />
</id>
<property name="userName" type="java.lang.String">
<column name="user_name" />
</property>

<set name="orders" inverse="true" cascade="all-delete-orphan" fetch="join" lazy="false">
<key column="USER_ID"></key>
<one-to-many class="TOrder"/>
</set>
</class>

<class name="TOrder" table="t_order" catalog="test">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="native" />
</id>
<property name="orderName" type="java.lang.String">
<column name="ORDER_NAME" length="20" />
</property>
<many-to-one name="user" class="TUser" >
<column name="USER_ID"></column>
</many-to-one>
</class>



2. 测试

(1) List list = session.createQuery("from TUser").list();

(2) List list = session.createQuery("from TUser where id=3 ").list();

(3) TUser u = (TUser)session.get(TUser.class, new Long(3));



3. 结论:

(1) fetch策略用于定义 get/load一个对象时，如何获取非lazy的对象/集合。

该定义在条件查询中无效。

(2) lazy=true 或false对join fetch没有任何影响, 均会使用左外连接。