Mybatis中的延迟加载,以及原理分析

<!-- 延迟加载设置-->
<setting name="lazyLoadingEnabled" value="true"/>
<setting name="aggressiveLazyLoading" value="false"/>

Role findRoleById(int roleId); //RoleDao中添加
<!--    延迟加载（懒加载）-->
<resultMap id="lazyMap" type="com.demo.entity.User">
    <id column="id" property="id"/>
    <result column="username" property="username"/>
    <result column="password" property="password"/>
    <association property="role" column="role_id" select="com.demo.dao.RoleDao.findRoleById"> 需要在RoleDao里面添加findRoleById方法
    </association>
</resultMap>

<select id="findList" resultMap="lazyMap" >
    select id,
           username,
           password,
           role_id 对应association.column 
    from tb_users
</select>

<resultMap id="roleMap2" type="com.demo.entity.Role">
    <id column="id" property="id"/>
    <result column="role_name" property="roleName"/>
    <result column="role_state" property="roleState"/>
</resultMap>

<select id="findRoleById" resultMap="roleMap2">
    select id, role_name, role_state
    from tb_role
    where id = #{role_id}
</select>

List<User> list = mapper.findList();
for (User user : list) {
    System.out.println(user.getId() + ", " + user.getUsername() + ", " + user.getPassword() );
    System.out.println(user.getRole().getId() + ", "+ user.getRole().getRoleName());
}