解决mybatis实体类和数据库列名不匹配的两种办法

我们在实际开发中，会遇到实体类与数据库类不匹配的情况，在开发中就会产生各种各样的错误，那么我们应该怎么去解决这一类的错误呢？很简单，下面我们介绍两种解决方法：
首先我们看一下数据库和实体类不匹配的情况：

解决办法1

当我们查询的时候我们可以在映射文件mapper.xml中采取取别名的方式：

	 <select id="findAll" resultMap="cn.com.scitc.domian.User" >
       select id as userId,username as userName,birthday as userBirthday,sex as userSex,address as userAddress from user
    </select>
 <!--配置查询所有-->
    <select id="findAll" resultType="cn.com.scitc.domian.User" >
--       select id as userId,username as userName,birthday as userBirthday,sex as userSex,address as userAddress from user
          select * from user;
    </select>

    <!--save-->
    <insert id="saveUser" parameterType="cn.com.scitc.domian.User">
<!-- 配置插入操作后，获取插入数据的id  keyProperty实体类  keyColum是数据库的值 order什么时候操作-->
    <selectKey keyProperty="id" keyColumn="id" resultType="int" order="AFTER" >
        select last_insert_id()
    </selectKey>
        insert into user (username,birthday,sex,address) values (#{userName},#{userBirthday},#{userSex},#{userAddress});
    </insert>

    <!--update-->
    <update id="updateUser" parameterType="cn.com.scitc.domian.User">
        update user set username = #{userName},birthday=#{userBirthday},sex=#{userSex},address=#{userAddress} where id=#{id}
    </update>

<!--delete-->
    <delete id="deleteUser" parameterType="int">
        delete from user where id = #{id}
    </delete>

    <!--用id 查询一个  交代清楚返回的结果-->
    <select id="findById" parameterType="Integer" resultType="cn.com.scitc.domian.User">
        select * from user where id = #{userId}
    </select>

    <!--username模糊查询-->
    <select id="fingByName" parameterType="string" resultType="cn.com.scitc.domian.User">
        select * from user where username like #{userName}

    </select>

我们再看看接口和测试类
接口dao中

	public interface UserDao {

//    查询所有
//    @Select("select * from user")
    List<User> findAll();

//    save
    void saveUser(User user);

//    update
    void updateUser(User user);

//    delete
    void deleteUser(Integer userId);

//    查询一个
    User findById(Integer userId);

//    根据名称 模糊查询
    List<User> fingByName(String username);

}

实现类：

public class MybatisTest {

//    初始化值
    private InputStream in;
    private SqlSession sqlSession;
    private UserDao userDao;

//    在测试方法执行之前执行
    @Before
    public void init() throws Exception{
//        读取文件
        in = Resources.getResourceAsStream("mybatis-Config.xml");
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        sqlSession = factory.openSession();
        userDao = sqlSession.getMapper(UserDao.class);
    }

    @After
    public void destory() throws Exception{

//        提交事务
        sqlSession.commit();
//        释放资源
        sqlSession.close();;
        in.close();
    }


    @Test
    public void testFindAll() throws Exception{
            List<User> users = userDao.findAll();
            for (User user : users){
                System.out.println("对象有："+user);
            }

    }


//    saveTest
    @Test
    public void TestSave() {
        User user = new User();
        user.setUserName("modify 修改");
        user.setUserBirthday(new Date());

        System.out.println("保存方法之前"+user);
        user.setUserSex("男");
        user.setUserAddress("天津");

        userDao.saveUser(user);
        System.out.println("保存方法之后"+user);
    }

//    update
    @Test
    public void TestUpdate() {
        User user = new User();
        user.setUserId(5);
        user.setUserName("aa");
        user.setUserBirthday(new Date());
        user.setUserSex("男");
        user.setUserAddress("德阳");

        userDao.updateUser(user);

    }

    @Test
    public void TestDelete(){
        userDao.deleteUser(5);
    }

//    findById
    @Test
    public void findById(){
        User user = userDao.findById(3);
        System.out.println(user);
    }


//username模糊查询
    @Test
    public void TestFindByName(){
        List<User> users = userDao.fingByName("%李%");
//        List<User> users = userDao.fingByName("李四");
        for (User user:users){
            System.out.println(user);
        }
    }

    //查询总记录数
    @Test
    public void findTotal(){
        int count = userDao.findTotal();
        System.out.println(count);
    }


    //username模糊查询
    @Test
    public void TestQuery(){
        QueryVo queryVo = new QueryVo();
        User user = new User();
        user.setUserName("%李%");
        queryVo.setUser(user);
        List<User> userByVo = userDao.findUserByVo(queryVo);
        for (User u:userByVo){
            System.out.println(u);
        }
    }

}

解决办法2

配置查询结果的列名和实体类的属性名对应的关系
依然是映射文件

 <!--配置查询结果的列名 和实体类的属性名对应的关系-->
    <resultMap id="userMap" type="cn.com.scitc.domian.User">
        <!--主键字段对应名-->
        <id property="userId" column="id"></id>
        <!--非主键字段的对应 property是实体类严格区分大小写 column数据库字段严格按照数据库字段 -->
        <result property="userName" column="username"></result>
        <result property="userBirthday" column="birthday"></result>
        <result property="userSex" column="sex"></result>
        <result property="userAddress" column="address"></result>
    </resultMap>

我们在mapper.xml文件中配置这些配置的作用就是与数据库进行关联：
=注意
主键 ：实体类的主键id一定要和数据库的主键id写对
property：是实体类严格区分大小写
column数据库字段严格按照数据库字段

配置好这些 我们就开始引用。

<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace dao权限类名===别名-->
<mapper namespace="cn.com.scitc.dao.UserDao">
    <!--配置查询结果的列名 和实体类的属性名对应的关系-->
    <resultMap id="userMap" type="cn.com.scitc.domian.User">
        <!--主键字段对应名-->
        <id property="userId" column="id"></id>
        <!--非主键字段的对应 property是实体类严格区分大小写 column数据库字段严格按照数据库字段 -->
        <result property="userName" column="username"></result>
        <result property="userBirthday" column="birthday"></result>
        <result property="userSex" column="sex"></result>
        <result property="userAddress" column="address"></result>
    </resultMap>

    <!--配置查询所有-->
    <select id="findAll" resultType="userMap" >
--       select id as userId,username as userName,birthday as userBirthday,sex as userSex,address as userAddress from user
          select * from user;
    </select>

    <!--save-->
    <insert id="saveUser" parameterType="userMap">
<!-- 配置插入操作后，获取插入数据的id  keyProperty实体类  keyColum是数据库的值 order什么时候操作-->
    <selectKey keyProperty="id" keyColumn="id" resultType="int" order="AFTER" >
        select last_insert_id()
    </selectKey>
        insert into user (username,birthday,sex,address) values (#{userName},#{userBirthday},#{userSex},#{userAddress});
    </insert>

    <!--update-->
    <update id="updateUser" parameterType="userMap">
        update user set username = #{userName},birthday=#{userBirthday},sex=#{userSex},address=#{userAddress} where id=#{id}
    </update>

<!--delete-->
    <delete id="deleteUser" parameterType="int">
        delete from user where id = #{id}
    </delete>

    <!--用id 查询一个  交代清楚返回的结果-->
    <select id="findById" parameterType="Integer" resultType="userMap">
        select * from user where id = #{userId}
    </select>

    <!--username模糊查询-->
    <select id="fingByName" parameterType="string" resultType="userMap">
        select * from user where username like #{userName}

    </select>

    <!--username模糊查询  第二种写法-->
    <!--<select id="fingByName" parameterType="string" resultType="cn.com.scitc.domian.User">-->
        <!--select *from user where username like '%${value}%'-->
    <!--</select>-->

    <!--获取用户总记录条数-->
    <select id="findTotal" resultType="int">
        select count(id) from user
    </select>

    <!--根据queryVo的条件查询用户-->
    <select id="findUserByVo" parameterType="cn.com.scitc.domian.QueryVo" resultType="UserMap">
          select * from user where username like #{user.userName}
    </select>

</mapper>

就是相当于把每一个要执行的sql语句的resultType的参数换成resultMap的值。
最后在进行测试就OK.。