Mybatis多表查询

一、一对一查询

<mapper namespace="com.finnlee.mapper.OrderMapper">
　　<resultMap id="orderMap" type="com.finnlee.pojo.Order">
　　　　<result column="uid" property="user.id"></result>
　　　　<result column="username" property="user.username"></result>
　　　　<result column="password" property="user.password"></result>
　　　　<result column="birthday" property="user.birthday"></result>
　　</resultMap>
　　<select id="findAll" resultMap="orderMap">
　　　　select * from orders o,user u where o.uid=u.id
　　</select>
</mapper>

　　

<resultMap id="orderMap" type="com.finnlee.pojo.Order">
　　<result property="id" column="id"></result>
　　<result property="ordertime" column="ordertime"></result>
　　<result property="total" column="total"></result>
　　<!-- property="user" 当前实体属性名   javaType="com.finnlee.pojo.User" 当前实体属性类型 -->
　　<association property="user" javaType="com.finnlee.pojo.User">
　　　　<result column="uid" property="id"></result>
　　　　<result column="username" property="username"></result>
　　　　<result column="password" property="password"></result>
　　　　<result column="birthday" property="birthday"></result>
　　</association>
</resultMap>

　　

二、一对多|多对多查询

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.finnlee.mapper.MemberMapper">
    <resultMap id="memberMap" type="com.finnlee.pojo.Member">
        <id column="id" property="id"></id>
        <result column="username" property="username" ></result>
        <collection property="orderList" ofType="com.finnlee.pojo.Order" >
            <result column="order_id" property="id"></result>
            <result column="order_sn" property="order_sn"></result>
        </collection>
        <collection property="roleGroup" ofType="com.finnlee.pojo.RoleGroup" >
            <result column="title" property="title"></result>
        </collection>
    </resultMap>
    <select id="findAll" resultMap="memberMap">
        select a.id,a.username ,b.order_sn ,b.id AS order_id,c.title from `member` a LEFT JOIN `order` b ON a.id = b.mid
        LEFT JOIN role_group c ON a.id = c.mid
    </select>
</mapper>