MyBatis深入解读懒加载的实现

<settings>
    <!--指定哪些方法去触发延迟加载,hashCode,equals,clone,toString-->
    <setting name="lazyLoadTriggerMethods" value=""/>
</settings>

Employee selectOneEmployee(int id);

<!--定义resultMap-->
<resultMap id="employeeMap1" type="Employee">
   <id column="id" property="id"/>
   <result property="name" column="name"/>
   <result property="age" column="age"/>
   <!--fetchType为查询的类型,这里选择lazy  select为嵌套查询-->
   <association property="dept" javaType="Dept" fetchType="lazy"
         select="selectDept" column="deptId">
   <result column="name" property="name"/>
   </association>
</resultMap>
<select id="selectOneEmployee" resultMap="employeeMap1">
   select id,name,age,deptId from employee where id=#{id}
</select>
<!--通过上一级sql提供的deptId查询-->
<select id="selectDept" resultType="Dept">
   select name from dept where id=#{deptId}
</select>

public static void main(String[] args) {
   SqlSession sqlSession= MybatisUtil.getSqlSession();
   EmployeeDao mapper=sqlSession.getMapper(EmployeeDao.class);
   Employee employee = mapper.selectOneEmployee(3);
   System.out.println(employee);
   System.out.println(employee.getDept());
   sqlSession.commit();  //提交事务
   sqlSession.close();   //关闭

<resultMap id="deptMap1" type="Dept">
    <id column="id" property="id"/>
    <result column="name" property="name"/>
    <!--collection为一对多 , 这里一个部门包含多个员工-->
    <collection property="list" javaType="List" ofType="Employee"
          select="selectEmployee" fetchType="lazy" column="id">
    <result property="name" column="name"/>
    </collection>
</resultMap>
<select id="selectOneDept" resultMap="deptMap1">
    SELECT id,name FROM dept where id=#{id}
</select>
<select id="selectEmployee" resultType="Employee">
    select name from employee where deptId=#{id}
</select>