一，基本環境

自己寫個demo，習慣性的使用generator逆向生成程式碼。

這是我的mapper.xml檔案。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mapping.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.byk.rong.system.mapper.read.UserReadMapper">
  <resultMap id="BaseResultMap" type="com.byk.rong.system.entity.User">
    <id column="id" jdbcType="VARCHAR" property="id" />
    <result column="user_name" jdbcType="VARCHAR" property="userName" />
    <result column="real_name" jdbcType="VARCHAR" property="realName" />
    <result column="password" jdbcType="VARCHAR" property="password" />
    <result column="salt" jdbcType="VARCHAR" property="salt" />
    <result column="dept_id" jdbcType="VARCHAR" property="deptId" />
    <result column="email" jdbcType="VARCHAR" property="email" />
    <result column="mobile" jdbcType="VARCHAR" property="mobile" />
    <result column="ID_card_number" jdbcType="VARCHAR" property="idCardNumber" />
    <result column="sex" jdbcType="VARCHAR" property="sex" />
    <result column="pictrue" jdbcType="VARCHAR" property="pictrue" />
    <result column="status" jdbcType="VARCHAR" property="status" />
    <result column="city_id" jdbcType="VARCHAR" property="cityId" />
    <result column="hobby" jdbcType="VARCHAR" property="hobby" />
    <result column="remarks" jdbcType="VARCHAR" property="remarks" />
    <result column="create_user" jdbcType="VARCHAR" property="createUser" />
    <result column="create_time" jdbcType="TIMESTAMP" property="createTime" />
    <result column="update_user" jdbcType="VARCHAR" property="updateUser" />
    <result column="update_time" jdbcType="TIMESTAMP" property="updateTime" />
    <result column="delete_user" jdbcType="VARCHAR" property="deleteUser" />
    <result column="delete_time" jdbcType="TIMESTAMP" property="deleteTime" />
    <result column="del_flag" jdbcType="VARCHAR" property="delFlag" />
  </resultMap>
  <sql id="Base_Column_List">
      id,
      user_name,
      real_name,
      password,
      salt ,
      dept_id,
      email,
      mobile,
      ID_card_number,
      sex,
      pictrue,
      status,
      city_id ,
      hobby,
      remarks,
      create_user,
      create_time,
      update_user,
      update_time,
      delete_user,
      delete_time,
      del_flag
        
  </sql>
  <select id="selectById" parameterType="java.lang.String" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from user
    where id = #{id,jdbcType=VARCHAR}  AND  del_flag = '0'
  </select>

  <select id="selectByParams" resultType="com.byk.rong.system.entity.User">
    select
    <include refid="Base_Column_List" />
    from user 
    <where>
      <if test="id != null and id != ''">and id = #{id}</if>
      <if test="userName != null and userName != ''">and user_name = #{userName}</if>
      <if test="realName != null and realName != ''">and real_name = #{realName}</if>
      <if test="password != null and password != ''">and password = #{password}</if>
      <if test="salt != null and salt != ''">and salt = #{salt}</if>
      <if test="deptId != null and deptId != ''">and dept_id = #{deptId}</if>
      <if test="email != null and email != ''">and email = #{email}</if>
      <if test="mobile != null and mobile != ''">and mobile = #{mobile}</if>
      <if test="idCardNumber != null and idCardNumber != ''">and ID_card_number = #{idCardNumber}</if>
      <if test="sex != null and sex != ''">and sex = #{sex}</if>
      <if test="pictrue != null and pictrue != ''">and pictrue = #{pictrue}</if>
      <if test="status != null and status != ''">and status = #{status}</if>
      <if test="cityId != null and cityId != ''">and city_id = #{cityId}</if>
      <if test="hobby != null and hobby != ''">and hobby = #{hobby}</if>
      <if test="remarks != null and remarks != ''">and remarks = #{remarks}</if>
      <if test="createUser != null and createUser != ''">and create_user = #{createUser}</if>
      <if test="createTime != null and createTime != ''">and create_time = #{createTime}</if>
      <if test="updateUser != null and updateUser != ''">and update_user = #{updateUser}</if>
      <if test="updateTime != null and updateTime != ''">and update_time = #{updateTime}</if>
      <if test="deleteUser != null and deleteUser != ''">and delete_user = #{deleteUser}</if>
      <if test="deleteTime != null and deleteTime != ''">and delete_time = #{deleteTime}</if>
      and del_flag = '0'
    </where>
    order by create_time desc
    <if test="offset != null and limit != null">
      limit #{offset}, #{limit}
    </if>
  </select>


    <select id="findByUsername" parameterType="java.lang.String" resultMap="BaseResultMap">
        select
        <include refid="Base_Column_List" />
        from user
        where user_name = #{userName,jdbcType=VARCHAR}  AND  del_flag = '0'
    </select>

</mapper>
 

然而，測試的時候發現實體類裡面的屬性對映不完整，一些欄位明明有值，但是輸出的實體類裡面相對應的屬性值為null，如下：

對比了一下，問題都出現在帶有“_”的欄位，也就是使用到駝峰命名的屬性上。

查詢資料，發現了問題所在。

二、解決辦法

第一種解決辦法

  <select id="selectByParams" resultType="com.byk.rong.system.entity.User">

這個方法是我自己寫的，使用了resultType，直接對映到實體類，沒有通過mabatis提供的 BaseResultMap，因此對映失敗，將這裡的resultType改成 resultMap="BaseResultMap"

第二種解決辦法

修改sql語句，即

 <sql id="Base_Column_List">
      id AS id,
      user_name AS userName,
      real_name AS realName,
      password as password,
      salt as salt,
      dept_id AS deptId,
      email as email,
      mobile as mobile,
      ID_card_number as   idCardNumber,
      sex as sex,
      pictrue as pictrue,
      status as status,
      city_id as cityId,
      hobby as hobby,
      remarks as remarks,
      create_user as createUser,
      create_time as createTime,
      update_user as updateUser,
      update_time as updateTime,
      delete_user as deleteUser,
      delete_time as deleteTime,
      del_flag AS delFlag
  </sql>
 

這樣，查詢到的欄位資料直接對映成屬性，也能解決這個問題。

效果如下：

注意：

這兩種辦法只能二選一，不能同時使用。