MyBatis之association嵌套

表、實體類、myBatisConfig.xml文件、以及測試類請看MyBatis之一對一關聯 ，沒必要再複製一遍這些內容

嵌套resultMap：

<?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="sysUser3">
  <resultMap type="com.chensan.sys.entity.SysUser3" id="sys_user3" autoMapping="true">
    <id property="id" column="id"/>
    <result property="company" column="company"/>
    <result property="salary" column="salary"/>

    <association property="idCard" column="card_id" resultMap="idCard1Mapper"/>
  </resultMap>

  <resultMap type="com.chensan.identity.entity.IdCard1" id="idCard1Mapper" autoMapping="true">
    <result property="cardNo" column="card_no"/>
    <result property="userName" column="user_name"/>
  </resultMap>

  <!-- 一對一：一個用戶對應一份身份信息 -->
  <!-- 方式二：嵌套resultMap查詢 -->
  <select id="getUserIdCard1" parameterType="int" resultMap="sys_user3">
    SELECT * FROM `sys_user3` t1, `id_card1` t2
    WHERE t1.`card_id`=t2.`id`
    AND t1.`id`=#{id}
  </select>
</mapper>

嵌套select語句：

<?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="sysUser3">
  <!-- 一對一：一個用戶對應一份身份信息 -->
  <!-- 方式二：嵌套select語句查詢 -->
  <select id="getUserIdCard1" parameterType="int" resultMap="sys_user3">
    SELECT * FROM `sys_user3` WHERE `id`=#{id}
  </select>

  <select id="getCardInfo" parameterType="int" resultMap="idCard1Mapper">
    SELECT * FROM `id_card1` WHERE `id`=#{id}
  </select>

  <resultMap type="com.chensan.sys.entity.SysUser3" id="sys_user3" autoMapping="true">
    <id property="id" column="id"/>
    <result property="company" column="company"/>
    <result property="salary" column="salary"/>

    <association property="idCard" column="card_id" select="getCardInfo"/>
  </resultMap>

  <resultMap type="com.chensan.identity.entity.IdCard1" id="idCard1Mapper" autoMapping="true">
    <result property="cardNo" column="card_no"/>
    <result property="userName" column="user_name"/>
  </resultMap>
</mapper>

association直接寫result和association引用resultMap應該算是差不多的用法，然後嵌套select語句查詢爲另一種方式，那麼select語句這種方式是否可不用resultMap，而把result放在association呢？事實證明，行不通。被實體屬性與數據表列不同名的，列出對應關係仍爲null（功力尚欠，這個問題就暫不做深究）；

實例如下：

<?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="sysUser3">
  <!-- 一對一：一個用戶對應一份身份信息 -->
  <select id="getUserIdCard1" parameterType="int" resultMap="sys_user3">
    SELECT * FROM `sys_user3` WHERE `id`=#{id}
  </select>

  <select id="getCardInfo" parameterType="int" resultType="com.chensan.identity.entity.IdCard1">
    SELECT * FROM `id_card1` WHERE `id`=#{id}
  </select>

  <resultMap type="com.chensan.sys.entity.SysUser3" id="sys_user3" autoMapping="true">
    <id property="id" column="id"/>
    <result property="company" column="company"/>
    <result property="salary" column="salary"/>

    <association property="idCard" column="card_id"
      javaType="com.chensan.identity.entity.IdCard1" autoMapping="true"
      select="getCardInfo">
      <result property="cardNo" column="card_no"/>
      <result property="userName" column="user_name"/>
    </association>
  </resultMap>

</mapper>

association嵌套參考：MyBatis association的兩種形式

始終覺得嵌套select語句查詢的條件不夠靈活