MyBatis学习总结_13_Mybatis查询之resultMap和resultType区别

╰半夏微凉° 2022-04-05 14:12 119阅读 0赞

# 轉載：[https://www.cnblogs.com/kluan/p/5934623.html][https_www.cnblogs.com_kluan_p_5934623.html] #

**MyBatis的每一个查询映射的返回类型都是ResultMap，只是当我们提供的返回类型属性是resultType的时候，MyBatis对自动的给我们把对应的值赋给resultType所指定对象的属性，而当我们提供的返回类型是resultMap的时候，将[数据库][Link 1]中列数据复制到对象的相应属性上，可以用于复制查询，两者不能同时用。**

**1、resultType**

**返回单个实例**

**<select id="selectUser" parameterType="int" resultType="User">**

**select \* from user where id = \#\{id\}**

**</select>  
返回List集合**

**<select id="selectUserAll" resultType="User" >   
select \* from user  
</select>**

**2、resultMap**

**简单查询：**

**<resultMap type="User" id="userMap">  
<id column="id" property="id"/>  
<result column="name" property="name"/>  
</resultMap>  
column:数据库中列名称，property:类中属性名称**

**resultMap：适合使用返回值是自定义实体类的情况**

**resultType：适合使用返回值得数据类型是非自定义的，即jdk的提供的类型**

**resultMap ： **

**映射实体类的数据类型**

**resultMap的唯一标识**

**column: 库表的字段名**

**property： 实体类里的属性名**

**配置映射文件：**

<?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.hao947.sql.mapper.PersonMapper">
      
      <resultMap type="person" id="BaseResultMap">
        
        <id column="person_id" property="personId" />
        <result column="name" property="name" />
        <result column="gender" property="gender" />
        <result column="person_addr" property="personAddr" />
        <result column="birthday" property="birthday" />
      </resultMap>
      
    
      
      <select id="selectPersonById" parameterType="java.lang.Integer"
        resultMap="BaseResultMap">
        select * from person p where p.person_id = #{id}
      </select>
      
      <select id="selectPersonCount" resultType="java.lang.Integer">
        select count(*) from
        person
      </select>
    
      <select id="selectPersonByIdWithMap" parameterType="java.lang.Integer"
        resultType="java.util.Map">
        select * from person p where p.person_id= #{id}
        </select>
    
    </mapper>

**实体类Person.[Java][]**

<pre name="code" class="java">package com.hao947.model;
    import java.util.Date;
    public class Person {
      private Integer personId;
      private String name;
      private Integer gender;
      private String personAddr;
      private Date birthday;
      @Override
      public String toString() {
        return "Person [personId=" + personId + ", name=" + name + ", gender="
            + gender + ", personAddr=" + personAddr + ", birthday="
            + birthday + "]";
      }
    }

**测试类**

public class PersonTest {
      SqlSessionFactory sqlSessionFactory;
      @Before
      public void setUp() throws Exception {
        // 读取资源流
        InputStream in = Resources.getResourceAsStream("sqlMapConfig.xml");
        // 初始化session工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
      }
    
      
    
      @Test
      public void selectPersonById() {
        // 创建一个sqlsession
        SqlSession session = sqlSessionFactory.openSession();
        try {
          Person p = session.selectOne(
              "com.hao947.sql.mapper.PersonMapper.selectPersonById", 1);
          System.out.println(p);
        } finally {
          session.close();
        }
      }
      @Test
      public void selectPersonCount() {
        // 创建一个sqlsession
        SqlSession session = sqlSessionFactory.openSession();
        try {
          Integer p = session.selectOne(
              "com.hao947.sql.mapper.PersonMapper.selectPersonCount");
          System.out.println(p);
        } finally {
          session.close();
        }
      }
      @Test
      public void selectPersonByIdWithMap() {
        // 创建一个sqlsession
        SqlSession session = sqlSessionFactory.openSession();
        try {
          Map<String ,Object> map = session.selectOne(
              "com.hao947.sql.mapper.PersonMapper.selectPersonByIdWithMap",1);
          System.out.println(map);
        } finally {
          session.close();
        }
      }
    }

[https_www.cnblogs.com_kluan_p_5934623.html]: https://www.cnblogs.com/kluan/p/5934623.html
[Link 1]: http://lib.csdn.net/base/mysql
[Java]: http://lib.csdn.net/base/javaee