MyBatis - 实体类的属性名和数据库列名不一致时的两种解决办法!

问题:两者不一致时 , 查询结果无法封装到实体!(也就无法查询出来)

① 查询的sql语句中使用别名进行查询.

<!--  namespace:接口的全路径名.  -->
<mapper namespace="com.xxx.dao.UserMapper">
	<!-- 使用别名 --> 
    <select id="queryAll" resultType="com.xxx.domain.User">
        select 
        	id as userId,
        	username as userName,
            address as userAddress,
            sex as userSex,
            birthday as userBirthday 
        from user;
    </select>
</mapper>

注: 如果使用别名 , 每一个sql语句都需要加别名 (很麻烦)
故: 一般都使用第二种.

② 使用resultMap ★

UserMapper.xml

<mapper namespace="com.jxj.dao.UserDao">
    <resultMap id="userResultMap" type="User">
    	<!-- 
    		主键字段  
    		    property: 实体类属性名.
    		    column: 库中表的列名
    		    javaType: 数据类型.
    	--> 
        <id property="userId" column="id" javaType="int"></id>
        <!-- 非主键字段  --> 
        <result property="userSex" column="sex" javaType="string"></result>
        <result property="userAddress" column="address" javaType="string"></result>
        <result property="userBirthday" column="birthday" javaType="date"></result>
        <result property="username" column="username" javaType="string"></result>
    </resultMap>

    <select id="queryAll"  resultMap="userResultMap">
        select * from user
    </select>

注: select中resultMap的属性值 要和 resultMap中id的属性值一样.

测试类: UserMapper.java

@Test
public void queryAll() throws IOException {
    // 1.创建工厂类.
    InputStream in = Resources.getResourceAsStream("mybatis-config.xml");
    SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
    // 2.创建sql对象.
    SqlSession sqlSession = sqlSessionFactory.openSession();
    // 3.创建接口的实现类对象.
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    // 4.调用接口中的方法 (代理)
    List<User> users = mapper.queryAll();
    for (User user : users) {
        System.out.println(user);
    }
    sqlSession.close();
    in.close();
}