MyBatis-resultType

朱雀 2022-05-17 08:11 197阅读 0赞

*   *  摘要
     *  正文
        
         *  查询单条记录返回对象
         *  查询多条记录返回List
         *  查询单条记录返回Map
         *  查询多条记录返回Map

## 摘要 ##

本文针对XML配置和注解配置说明resultType用法

## 正文 ##

下面的例子都用过查询User类实现

### 查询单条记录返回对象 ###

*  XML配置

<?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.example.UserMapper">
        
        <select id="findById" resultType="com.example.User">
            select * from user where id=#{id}
        </select>
    </mapper>

*  注解配置

public interface UserMapper{ 
        @Select("select * from user where id=#{id}")
        User findById(Long id);
    }

### 查询多条记录返回List ###

*  XML配置

<?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.example.UserMapper">
        
        <select id="findList" resultType="com.example.User">
            select * from user
        </select>
    </mapper>

*  注解配置

public interface UserMapper{ 
        @Select("select * from user")
        List<User> findList();
    }

### 查询单条记录返回Map ###

在没有查询结果没有实体类的情况，我会使用这种方式。

*  XML配置

<?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.example.UserMapper">
        
        <select id="findById" resultType="map">
            select * from user where id=#{id}
        </select>
    </mapper>

*  注解配置

public interface UserMapper{ 
        @Select("select * from user where id=#{id}")
        Map<String,Object> findById(Long id);
    }

### 查询多条记录返回Map ###

对部分列需要处理时，我会使用这种方式

*  XML配置

<?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.example.UserMapper">
        
        <select id="findMap" resultType="com.example.User">
            select * from user
        </select>
    </mapper>
    
    public interface UserMapper{
        // 通过@MapKey注解指定作为key的列名
        @MapKey("id")
        Map<Long,User> findMap();
    }

*  注解配置

public interface UserMapper{ 
        @MapKey("id")
        @Select("select * from user")
        Map<Long,User> findMap();
    }