8. Development using annotations

8.1 Interface-oriented development

three facets of difference

Object-oriented means that when we consider a problem, we take the object as a unit and consider its properties and methods;

Process-oriented means that when we consider a problem, we take a specific process (business process) as a unit and consider its realization;

Interface design and non-interface design are for reuse technology, and object-oriented (process) is not a problem, but more reflected in the overall architecture of the system;

8.2 Development using annotations

1. Annotations are implemented on interfaces

   @Select("select * from mybatis.user")
    List<User> getUsers();

2. Binding in the core configuration file

<!--绑定接口-->
    <mappers>
        <mapper class="com.jiang.mapper.UserMapper"></mapper>
    </mappers>

3. Test

public class UserMapperTest {

    @Test
    public void test(){
        SqlSession sqlSesssion = MybatisUtils.getSqlSesssion();
        //底层主要应用反射
        UserMapper mapper = sqlSesssion.getMapper(UserMapper.class);
        List<User> users = mapper.getUsers();
        for (User user: users
             ) {
            System.out.println(user);
        }
        sqlSesssion.close();
    }

Essence: reflection mechanism implementation

Bottom layer: dynamic proxy

Mybatis detailed execution process

8.3 CRUD

We can automatically commit transactions when the tool class is created

 @Test
    public void test(){
        SqlSession sqlSesssion = MybatisUtils.getSqlSesssion();
        //底层主要应用反射
        UserMapper mapper = sqlSesssion.getMapper(UserMapper.class);
       /* User user = mapper.getUserById(1);
        System.out.println(user);*/
        /*for (User user: users
             ) {
            System.out.println(user);
        }*/
        mapper.addUser(new User(5,"youyou","123123"));

        sqlSesssion.close();
    }

 @Select("select * from mybatis.user")
    List<User> getUsers();

    //方法存在多个参数，所有的参数前面必须加上@Param
    @Select("select * from user where id=#{id}")
    User getUserById(@Param("id") int id);

    @Insert("insert into user(id,name,pwd)values(#{id},#{name},#{password})")
    int addUser(User user);

<!--绑定接口-->
    <mappers>
        <mapper class="com.jiang.mapper.UserMapper"></mapper>
    </mappers>

About @Param() annotation

Parameters of basic type or String type need to be added
Reference types do not need to add
If there is only one basic type, it can be ignored, but it is recommended that everyone add it
What we refer to in SQL is the attribute name set in our @Param() here

#{} and ${}

#There is pre-compiled meaning to prevent SQL injection

https://www.bilibili.com/video/BV1NE411Q7Nx?p=19&spm_id_from=pageDriver

MyBatis [developed using annotations]