一、数据库建表

 二、entity目录下创建user实体类

三、dao目录下创建userMapper映射接口 

@Mapper
public interface UserMapper {
    User selectById(int id);

    User selectByName(String username);

    User selectByEmail(String email);

    int insertUser(User user);

    int updateStatus(int id, int status);

    int updateHeader(int id, String headerUrl);

    int updatePassword(int id, String password);
}

四、创建user-mapper映射xml文件

xml文件的格式可以在mybatis官网找到，直接复制进文件就行。

<?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="com.nowcoder.community1.dao.UserMapper">
<!-- namespace里面写和哪个mapper对应-->
    <sql id="insertFields">
        username, password, salt, email, type, status, activation_code, header_url, create_time
    </sql>

    <sql id="selectFields">
        id, username, password, salt, email, type, status, activation_code, header_url, create_time
    </sql>

    <select id="selectById" resultType="User">
        select <include refid="selectFields"></include>
        from user
        where id = #{id}
    </select>

    <select id="selectByName" resultType="User">
        select <include refid="selectFields"></include>
        from user
        where username = #{username}
    </select>

    <select id="selectByEmail" resultType="User">
        select <include refid="selectFields"></include>
        from user
        where email = #{email}
    </select>

    <insert id="insertUser" parameterType="User" keyProperty="id">
        insert into user (<include refid="insertFields"></include>)
        values(#{username}, #{password}, #{salt}, #{email}, #{type}, #{status}, #{activationCode}, #{headerUrl}, #{createTime})
    </insert>

    <update id="updateStatus">
        update user set status = #{status} where id = #{id}
    </update>

    <update id="updateHeader">
        update user set header_url = #{headerUrl} where id = #{id}
    </update>

    <update id="updatePassword">
        update user set password = #{password} where id = #{id}
    </update>

</mapper>

五、测试从数据库中查找

@Test
public void testSelectUser() {
    User user = userMapper.selectById(101);
    System.out.println(user);

    user = userMapper.selectByName("liubei");
    System.out.println(user);

    user = userMapper.selectByEmail("nowcoder101@sina.com");
    System.out.println(user);
}