20160510--hibernate懒加载问题

懒加载

通过asm和cglib二个包实现；Domain是非final的。

1.session.load懒加载。

2.one-to-one(元素)懒加载：

必需同时满足下面三个条件时才能实现懒加载

(主表不能有constrained=true,所以主表没有懒加载)

lazy!=false 2)constrained=true 3)fetch=select

3.one-to-many (元素)懒加载：1)lazy!=false 2)fetch=select

4.many-to-one (元素) ：1)lazy!=false 2)fetch=select

5.many-to-many (元素) ：1)lazy!=false 2)fetch=select

6.能够懒加载的对象都是被改写过的代理对象，当相关联的session没有关闭时，访问这些懒加载对象（代理对象）的属性（getId和getClass除外）hibernate会初始化这些代理，或用Hibernate.initialize(proxy)来初始化代理对象；当相关联的session关闭后，再访问懒加载的对象将出现异常。

 一对一懒加载（对系统影响不算太大）

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.dzq.domain">

    <class name="IDCard" table="id_card">
        <id name="id" column="id">
            <generator class="foreign">
                <param name="property">person</param>
            </generator>
        <!--     <generator class="native"/> -->
        </id>
        <property name="name" column="name" />
        <one-to-one name="person" constrained="true" lazy="proxy" fetch="join"/>
    <!-- <many-to-one name="person" column="person_id" unique="true"/> -->
    </class>

</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.dzq.domain">

    <class name="Person" table="person">
        <id name="id" column="id">
            <generator class="native" />
        </id>
        <property name="name" column="name" />
         <one-to-one name="idcard"/>
        <!--  <one-to-one name="idcard" property-ref="person"/> -->
    </class>

</hibernate-mapping>

 多对一懒加载（影响性能，最好不禁用懒加载，使用hibernate初始化代理，解决）

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.dzq.domain">

    <class name="Department" table="department">
        <id name="id" column="id">
            <generator class="native" />
        </id>
        <property name="name" column="name" />
         <!-- <set name="empls" cascade="save-update">
            <key column="depart_id"/>
            <one-to-many class="Employee"/>
        </set> -->
        <set name="empls" inverse="true">
            <key column="depart_id"/>
            <one-to-many class="Employee"/>
        </set>
        <!-- <list name="empls">
            <key column="depart_id"/>
            <list-index column="order_col"/>
            <one-to-many class="Employee"/>
        </list> -->

        <!-- <bag name="empls">
            <key column="depart_id"/>
            <one-to-many class="Employee"/>
        </bag>
         -->

    </class>

</hibernate-mapping>

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.dzq.domain">

    <class name="Employee" table="employee" discriminator-value="0">
        <id name="id" column="id">
            <generator class="hilo" />
        </id>
        <!--  <discriminator column="type"/> -->
        <property name="name" column="name" />
        <many-to-one name="depart" column="depart_id" />
        <!-- <subclass name="Skiller" discriminator-value="1">
            <property name="skiller"/>
        </subclass>
        <subclass name="Sales" discriminator-value="2">
            <property name="sell"/>
        </subclass> -->
    <!--     <joined-subclass name="Skiller" table="skiller">
            <key column="emp_id"/>
            <property name="skiller"/>
        </joined-subclass>
        <joined-subclass name="Sales" table="sales">
            <key column="emp_id"/>
            <property name="sell"/>
        </joined-subclass> -->
        <!-- <subclass name="Skiller" discriminator-value="1">
            <property name="skiller"/>
        </subclass>
        <subclass name="Sales" discriminator-value="2">
            <join table="sales">
                <key column="emp_id"/>
                <property name="sell"/>
            </join>

        </subclass> -->
        <union-subclass name="Skiller">
            <property name="skiller"/>
        </union-subclass>
        <union-subclass name="Sales">
            <property name="sell"/>
        </union-subclass>
    </class>

</hibernate-mapping>

public static Department queryDepart(int id){
        Session s=null;
        try{
            s=HibernateUntils.getSession();
            Department depart=(Department) s.get(Department.class, id);
            Hibernate.initialize(depart.getEmpls());//hibernate初始化代理
            System.out.println(depart.getEmpls().getClass());
            return depart;
        }finally{
            if(s!=null){
                s.close();
            }
        }
    }

多对多懒加载（（更加影响性能，最好不禁用懒加载，使用hibernate初始化代理，解决））