2.mybatis的简单增删改查-优快云博客

本文链接：https://blog.youkuaiyun.com/wu_intellect/article/details/108230417

本文详细介绍了MyBatis框架中的CRUD操作，包括查询、插入、更新和删除等核心功能的实现方式，以及如何通过接口和SQL映射文件进行数据库交互。

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mybatis的crud

1.CRUD

1. namespance

namespace中的包名要和dao/mapper接口的包名一致!

2.select

选择,查询语句:

id:就是对应的namespace中的方法名;
resultType:sql语句执行的返回值;
parameterType:参数类型;

编写接口
```
User getById(int id);
```

编写对应的mapper中的sql语句

 <select id="getById" resultType="com.pojo.User" parameterType="int">
        select * from mybatis.user where id=#{id};
    </select>

测试

  public void getById(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User byId = mapper.getById(1);
        System.out.println(byId);
        sqlSession.close();
    }

3.insert

增加语句:

接口
```
int  insert(User user);
```

sql语句

<insert id="insert" parameterType="com.pojo.User">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>

测试

  @Test
    public void insert(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.insert(new User(4,"zhaoliu","159488"));
        sqlSession.commit();
        sqlSession.close();
    }

4.update

修改语句:

接口
```
int updataList(User user);
```

sql语句

 <update id="updataList" parameterType="com.pojo.User">
       update mybatis.user set `name`=#{name},pwd=#{pwd}  where id=#{id} ;
   </update>

测试

 @Test
    public void updata(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.updataList(new User(2,"wangwu","123456"));

        sqlSession.commit();
        sqlSession.close();
    }

5.delete

删除语句:

接口
```
int deleteUser(int id);
```

sql语句

<!--删除语句    -->
    <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id=#{id};
    </delete>

测试

    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(4);
        sqlSession.commit();
        sqlSession.close();
    }

注意点

增删改需要提交事务

6.万能的map

假设,我们的实体类,或者数据库中的表,字段或者参数过多,我们应当考虑使用Map!

接口
```
int insert2(Map<String,Object> map);
```

sql语句

 <!--map增加语句    -->
    <insert id="insert2" parameterType="map">
        insert into mybatis.user (id,name,pwd) values (#{userid},#{username},#{password});
    </insert>

测试

    @Test
    public void insert2(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("userid",4);
        map.put("username","tianqi");
        map.put("password","456789");
        mapper.insert2(map);
        
        sqlSession.commit();
        sqlSession.close();
    }

Map传递参数,直接在sql中取key即可! [parameterType=“map”]
对象传递参数,直接在sql中取对象的属性即可![parameterType=“Object”]
只有一个基本类型参数的情况下,可以直接在sql中取到!
多个参数用Map,或者注解

7.模糊查询

java代码执行的时候,传递通配符% %

  <!--模糊查询    -->
    <select id="getUserLike" resultType="com.pojo.User">
        select * from mybatis.user where `name` like #{value};
    </select>

    @Test
    public void getUserLike(){
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userLike = mapper.getUserLike("%wu%");
        for (User user : userLike) {
            System.out.println(user);
        }

        sqlSession.close();
    }

在sql拼接中使用通配符!

	<select id="getUserLike" resultType="com.pojo.User">
        select * from mybatis.user where `name` like "%"#{value}"%";
    </select>