MyBatis之注解开发

逃离我推掉我的手 2024-04-18 19:01 88阅读 0赞

# mybatis常用注解： #

@Insert:实现新增  
@Update:实现更新  
@Delete:实现删除  
@Select:实现查询  
@Result:实现结果集封装  
@Results:可以与@Result 一起使用，封装多个结果集  
@ResultMap:实现引用@Results 定义的封装  
@One:实现一对一结果集封装  
@Many:实现一对多结果集封装  
@SelectProvider: 实现动态 SQL 映射  
@CacheNamespace:实现注解二级缓存的使用

# 使用注解完成CRUD操作： #

public interface IUserDao {
    
        /**
         * 查询所有用户
         * @return
         */
        @Select("select * from user")
        List<User> findAll();
    
        /**
         * 保存用户
         * @param user
         */
        @Insert("insert into user(username,address,sex,birthday)values(#{username},#{address},#{sex},#{birthday})")
        void saveUser(User user);
    
        /**
         * 更新用户
         * @param user
         */
        @Update("update user set username=#{username},sex=#{sex},birthday=#{birthday},address=#{address} where id=#{id}")
        void updateUser(User user);
    
        /**
         * 删除用户
         * @param userId
         */
        @Delete("delete from user where id=#{id} ")
        void deleteUser(Integer userId);
    
        /**
         * 根据id查询用户
         * @param userId
         * @return
         */
        @Select("select * from user  where id=#{id} ")
        User findById(Integer userId);
    
        /**
         * 根据用户名称模糊查询
         * @param username
         * @return
         */
    //    @Select("select * from user where username like #{username} ")
        @Select("select * from user where username like '%${value}%' ")
        List<User> findUserByName(String username);
    
        /**
         * 查询总用户数量
         * @return
         */
        @Select("select count(*) from user ")
        int findTotalUser();
    }

# @Results、@Result、@ResultMap、@One注解 #

fetchType=FetchType.EAGER为立即加载，一般用在一对一  
fetchType=FetchType.LAZY为延迟加载，一般用在多对多

public interface IAccountDao {
    
        /**
         * 查询所有账户，并且获取每个账户所属的用户信息
         * @return
         */
        @Select("select * from account")
        @Results(id="accountMap",value = {
                @Result(id=true,column = "id",property = "id"),
                @Result(column = "uid",property = "uid"),
                @Result(column = "money",property = "money"),
                @Result(property = "user",column = "uid",one=@One(select="com.itheima.dao.IUserDao.findById",fetchType= FetchType.EAGER))
        })
        List<Account> findAll();
    }

com.itheima.dao.IUserDao.findById：

@Select("select * from user  where id=#{id} ")
        @ResultMap("userMap")
        User findById(Integer userId);

pojo类的写法：

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY5OTU2Mg_size_16_color_FFFFFF_t_70]

# @many注解 #

public interface IUserDao {
    
        /**
         * 查询所有用户
         * @return
         */
        @Select("select * from user")
        @Results(id="userMap",value={
                @Result(id=true,column = "id",property = "userId"),
                @Result(column = "username",property = "userName"),
                @Result(column = "address",property = "userAddress"),
                @Result(column = "sex",property = "userSex"),
                @Result(column = "birthday",property = "userBirthday"),
                @Result(property = "accounts",column = "id",
                        many = @Many(select = "com.itheima.dao.IAccountDao.findAccountByUid",
                                    fetchType = FetchType.LAZY))
        })
    }

com.itheima.dao.IAccountDao.findAccountByUid：

@Select("select * from account where uid = #{userId}")
        List<Account> findAccountByUid(Integer userId);

pojo类的写法:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY5OTU2Mg_size_16_color_FFFFFF_t_70 1]

# @CacheNamespace开启二级缓存 #

![在这里插入图片描述][20190910203942627.png]

开启二级缓存后，第一次查询会执行sql，第二次及以后的查询都会从缓存中读取数据

注意：开启缓存的弊端是数据没有实时性，当数据库中的数据一旦修改，查询的数据还是缓存中的数据没有实时性。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY5OTU2Mg_size_16_color_FFFFFF_t_70]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/b08aeec08ab54577980f8a7ddaf27b9d.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MTY5OTU2Mg_size_16_color_FFFFFF_t_70 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/15cc25680b354dafa815a15a9c664aa1.png
[20190910203942627.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/18/add2116d0fb7478489fe8c41a2aee483.png