Solve the problem of inconsistency between database field name and entity class attribute name (resultmap result set mapping)

Official documents

problem

 Database fields ：id	name	pwd
 Entity class properties ：id	name	password

Query results ：password Query as null

reason ：

sql sentence ：select * from mybatis.user where id = #{id}
 It's actually ：select id,name,pwd from mybatis.user where id = #{id}
 And the output user Of password Property has no assignment , So for null

resolvent ：
1. names （ understand ）

select id,name,pwd as password from mybatis.user where id = #{id}

2. Use resultMap Result set mapping

    <resultMap id="userMap" type="user">
        <!--property Properties in entity classes ,column Fields in the database -->
        <result property="password" column="pwd"/>
    </resultMap>

    <select id="getUserById" resultMap="userMap" parameterType="int">
        select * from mybatis.user where id = #{id}
    </select>