[MyBatis]ResultMap结果集映射

当数据库的列名和实体类的属性名不一致会导致查询失败，因此配置Result结果集映射。

如实体类为

package com.zlc.pojo;

import org.apache.ibatis.type.Alias;

//实体类
@Alias("user")
public class User {
    private int id;
    private String username;
    private String password;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public User(int id, String username, String password) {
        this.id = id;
        this.username = username;
        this.password = password;
    }

    public User() {
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

id username password

而数据库为

id name pwd

则配置映射

<?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">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.zlc.dao.UserMapper">

    <resultMap id="UserMap" type="User">
        <!--colum数据库中的字段，property中实体类的属性-->
        <result column="id" property="id"/>
        <result column="name" property="username"/>
        <result column="pwd" property="password"/>
    </resultMap>
    
    <select id="getUserById" parameterType="int" resultType="UserMap">
        select * from mybatis.user where id =#{id}
    </select>

</mapper>