【MyBatis】| MyBatis的注解式开发

Bertha 。 2024-03-30 16:46 75阅读 0赞

**目录**

一：MyBatis的注解式开发

1. @Insert注解

2. @Delete注解

3. @Update注解

4. @Select注解

5. @Results注解

--------------------

## 一：MyBatis的注解式开发 ##

> MyBatis中也提供了注解式开发⽅式，**采⽤注解可以减少SqlMapper映射⽂件的配置**。 当然，**使⽤注解式开发的话，sql语句是写在java程序中的**，这种⽅式也会给sql语句的维护带来成本。

官⽅是这么说的：

![1b040b538c944ae69484573270bc9ea6.png][]

使⽤注解编写复杂的SQL是这样的：

![a3faeed8d8a345408fd33f65393cf324.png][]

**原则：简单sql可以注解，复杂sql使⽤xml！**

使用注解式开发以后三兄弟之一的SqlMapper.xml文件就不需要了！

![47a1ca415b06475ab0ddeda4dfbb9b08.png][]

#### 1. @Insert注解 ####

二兄弟之一CarMapper接口，用来编写方法

> 使用@Insert的注解方式，在注解上就可以写上SQL语句，对于SQL语句当中的变量就是pojo类Car对应的变量名

package com.bjpowernode.mybatis.mapper;
    
    import com.bjpowernode.mybatis.pojo.Car;
    import org.apache.ibatis.annotations.Insert;
    
    public interface CarMapper {
        // 使用注解式开发，插入数据
        @Insert("insert into t_car values(null,#{carNum},#{brand},#{guidePrice},#{produceTime},#{carType})")
        int insert(Car car);
    }

二兄弟之二CarMapperTest，用来测试

package com.bjpowernode.mybatis.test;
    
    import com.bjpowernode.mybatis.mapper.CarMapper;
    import com.bjpowernode.mybatis.pojo.Car;
    import com.bjpowernode.mybatis.utils.SqlSessionUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    public class CarMapperTest {
        @Test
        public void testInsert(){
            SqlSession sqlSession = SqlSessionUtil.openSession();
            CarMapper mapper = sqlSession.getMapper(CarMapper.class);
            // 创建Car对象
            Car car = new Car(null, "666", "丰田霸道", 32.0, "2023-1-9", "燃油车");
            int count = mapper.insert(car);
            System.out.println(count);
            sqlSession.commit();
            sqlSession.close();
        }
    }

执行结果：

![47e27825a0724acea56cbb21703a1913.png][]

#### 2. @Delete注解 ####

二兄弟之一CarMapper接口，用来编写方法

package com.bjpowernode.mybatis.mapper;
    
    import com.bjpowernode.mybatis.pojo.Car;
    import org.apache.ibatis.annotations.Insert;
    
    public interface CarMapper {
        // 使用注解式开发，删除数据
        @Delete("delete from t_car where id = #{id}")
        int deleteById(Long id);
    }

二兄弟之二CarMapperTest，用来测试

package com.bjpowernode.mybatis.test;
    
    import com.bjpowernode.mybatis.mapper.CarMapper;
    import com.bjpowernode.mybatis.pojo.Car;
    import com.bjpowernode.mybatis.utils.SqlSessionUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    public class CarMapperTest {
       @Test
        public void testDeleteById(){
            SqlSession sqlSession = SqlSessionUtil.openSession();
            CarMapper mapper = sqlSession.getMapper(CarMapper.class);
            int count = mapper.deleteById(40L);
            System.out.println(count);
            sqlSession.commit();
            sqlSession.close();
        }
    }

执行结果：

![e1c58fdb61384adda9d7e3af822d531c.png][]

#### 3. @Update注解 ####

二兄弟之一CarMapper接口，用来编写方法

package com.bjpowernode.mybatis.mapper;
    
    import com.bjpowernode.mybatis.pojo.Car;
    import org.apache.ibatis.annotations.Insert;
    
    public interface CarMapper {
        // 使用注解式开发，更新数据
        @Update("update t_car set car_num=#{carNum},brand=#{brand},guide_price=#{guidePrice},produce_time=#{produceTime},car_type=#{carType} where id = #{id}")
        int update(Car car);
    }

二兄弟之二CarMapperTest，用来测试

package com.bjpowernode.mybatis.test;
    
    import com.bjpowernode.mybatis.mapper.CarMapper;
    import com.bjpowernode.mybatis.pojo.Car;
    import com.bjpowernode.mybatis.utils.SqlSessionUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    public class CarMapperTest {
       @Test
        public void testUpdate(){
            SqlSession sqlSession = SqlSessionUtil.openSession();
            CarMapper mapper = sqlSession.getMapper(CarMapper.class);
            // 创建Car对象，根据id进行更新
            Car car = new Car(34L, "666", "丰田霸道", 32.0, "2023-1-9", "燃油车");
            int count = mapper.update(car);
            System.out.println(count);
            sqlSession.commit();
            sqlSession.close();
        }
    }

执行结果：

![9192f516909545ad984b2db93fcfc5d6.png][]

#### 4. @Select注解 ####

二兄弟之一CarMapper接口，用来编写方法

package com.bjpowernode.mybatis.mapper;
    
    import com.bjpowernode.mybatis.pojo.Car;
    import org.apache.ibatis.annotations.Insert;
    
    public interface CarMapper {
        // 使用注解式开发，查询数据
        @Select("select * from t_car where id = #{id}")
        Car selectById(Long id);
    }

二兄弟之二CarMapperTest，用来测试

package com.bjpowernode.mybatis.test;
    
    import com.bjpowernode.mybatis.mapper.CarMapper;
    import com.bjpowernode.mybatis.pojo.Car;
    import com.bjpowernode.mybatis.utils.SqlSessionUtil;
    import org.apache.ibatis.session.SqlSession;
    import org.junit.Test;
    
    public class CarMapperTest {
       @Test
        public void testSelectById(){
            SqlSession sqlSession = SqlSessionUtil.openSession();
            CarMapper mapper = sqlSession.getMapper(CarMapper.class);
            Car car = mapper.selectById(41L);
            System.out.println(car);
            sqlSession.close();
        }
    }

执行结果：

![38df315038de45118fcc5f680630ec2d.png][]

#### 5. @Results注解 ####

> 我们知道数据库表中的字段和pojo类的属性名有的是不一样的，我们之所以能够完整的查出数据，是因为在核心配置文件mybatis-config.xml当中配置了：**启用驼峰命名⾃动映射**

<settings>
            <setting name="mapUnderscoreToCamelCase" value="true"/>
        </settings>

> 如果我们不启用，不对应的字段就是null，查询的数据如下：

![94deed52202541368930c97feff7ece2.png][]

**那还有什么办法呢？**

> **还可以使用@Results注解指定映射关系，Results注解就等同于结果映射ResultMap！**
> 
> **注：**@Results注解必须与@Select查询同方法在一起，不可以单独定义@Results注解！
> 
> 注：从这里也能看出，使用注解的方式开发，对于简单点的SQL还行，对于稍微复杂的查询语句就太麻烦了！

package com.bjpowernode.mybatis.mapper;
    
    import com.bjpowernode.mybatis.pojo.Car;
    import org.apache.ibatis.annotations.*;
    
    public interface CarMapper {
        // 使用注解式开发，查询数据
        @Select("select * from t_car where id = #{id}")
        @Results({
                @Result(property = "id",column = "id"),
                @Result(property = "carNum",column = "car_num"),
                @Result(property = "brand",column = "brand"),
                @Result(property = "guidePrice",column = "guide_price"),
                @Result(property = "produceTime",column = "produce_time"),
                @Result(property = "carType",column = "car_type"),
        })
        Car selectById(Long id);
    }

> 这样计算我们不启用驼峰命名⾃动映射，也能正常查询数据

![66b0a9e7ef7c4a07ae4983865a1124e6.png][]

**结语：直到今天MyBatis的学习就完美撒花了，接下来就开始Spring的学习，敬请期待！**

[1b040b538c944ae69484573270bc9ea6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/1cf334b3f1c64fb29ad874a6f2492ba3.png
[a3faeed8d8a345408fd33f65393cf324.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/8d5294f95b1a4d0fb7c16ce7230e7ade.png
[47a1ca415b06475ab0ddeda4dfbb9b08.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/cfcb40fd395c41d4ae334ea14a6a0635.png
[47e27825a0724acea56cbb21703a1913.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/8f1ad2c2733043008d2061169054b4cf.png
[e1c58fdb61384adda9d7e3af822d531c.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/52a40a20b34e43b38e46159b3afc0387.png
[9192f516909545ad984b2db93fcfc5d6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/333082827eef4ef49895fbaea99d0ec5.png
[38df315038de45118fcc5f680630ec2d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/5da8ca14998f46d5b98824eadbf32d5e.png
[94deed52202541368930c97feff7ece2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/c76af23e4ee942d19dbe47e853e39d8f.png
[66b0a9e7ef7c4a07ae4983865a1124e6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/30/97f0e907ba784c39887aca04d0ad552d.png