Mybatis-resultMap的一些用法（映射，关联查询）

通过resultMap来解决冲突

<select id="selll" resultMap="userMap">       
 select id u_id,name u_name,age u_age from users
    </select>
    <resultMap type="com.zhiyou100.xf.bean.Users" id="userMap">
        <id column="u_id" property="id"/><!--作为唯一标识-->
        <result column="u_name" property="name"/>
        <result column="u_age" property="age"/>
    </resultMap>

关联查询

一对一、多对一

实体类中将另一个类作为属性association

<!-方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1 -->

 <select id="getClass" parameterType="int" resultMap="ClassResultMap">
 select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id} 
</select> 
<resultMap type="_Classes" id="ClassResultMap">
 <id property="id" column="c_id"/> 
<result property="name" column="c_name"/>
 <association property="teacher" column="teacher_id" javaType="_Teacher">
 <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> 
</resultMap>
<!-
方式二：嵌套查询：通过执行另外一个 SQL 映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; SELECT*FROMteacherWHEREt_id=1 //1 是上一个查询得到的 teacher_id 的值
-->
<select id="getClass2" parameterType="int" resultMap="ClassResultMap2"> 
select * from class where c_id=#{id} 
</select> 
<resultMap type="_Classes" id="ClassResultMap2"> 
<id property="id" column="c_id"/> 
<result property="name" column="c_name"/>
 <association property="teacher" column="teacher_id" javaType="_Teacher" select="getTeacher">
 </association> 
</resultMap>
<select id="getTeacher" parameterType="int" resultType="_Teacher"> 
SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} 
</select>

一对多

实体类中将另一个类的list作为属性collection

<select id="selAll" resultMap="AllMap">
        select * from teacher,student,class where c_id=class_id and teacher_id=t_id and c_id=#{id}
    </select>
    <resultMap type="com.zhiyou100.xf.bean.Classes" id="AllMap">
        <id column="c_id" property="cid"/>
        <result column="c_name" property="cname"/>
        <association property="teacher" javaType="com.zhiyou100.xf.bean.Teacher">
            <id column="t_id" property="tid"/>
            <result column="t_name" property="tname"/>
        </association>
        <collection property="students" ofType="com.zhiyou100.xf.bean.Student">
            <id column="s_id" property="sid"/>
            <result column="s_name" property="sname"/>
        </collection>
    </resultMap>