mybatis 简单实现 left join

sql 

-- 表a       ta (id,aname,bid)
-- 表b       tb (id,bname)
SELECT T1.*, T2.BNAME FROM TA T1 LEFT JOIN TB T2 ON T1.BID = T2.ID 

xml

<resultMap id="BaseResultMap" type="com.zxg.pojo.Ta" >
    <id column="ID" property="id" jdbcType="CHAR" />
    <result column="ANAME" property="aName" jdbcType="VARCHAR" />
    <association column="BID" property="bName" select="com.zxg.dao.TbMapper.getTbNameById"/>  
  </resultMap>

  <select id="getTbNameById" resultType="java.lang.String" parameterType="java.lang.String" >
    SELECT BNAME FROM TB WHERE ID = #{id}
  </select>

• 内部调用不需要在mapper接口中定义（getTbNameById 只写到mapper.xml 中即可）
• 注：resultType or resultMap  和 association的property类型保持一致。

 association 传多个参数

<association column="{key1=COL1,key2=COL2}" property="pro" select="mapper.method"/>

• parameterType="java.util.Map"
• #{key1,jdbcType=VARCHAR}
• #{key2,jdbcType=VARCHAR}