**MyBatis - development using annotations**

8, Using annotation development

1. Interface oriented programming

• In real development, interface oriented programming is often chosen;
• Root cause: decoupling, scalability, improved reuse. In layered development, the upper layer does not care about the specific implementation. Everyone abides by common standards, making the development easier and more standardized.

Understanding of interfaces

• From a deeper understanding, the interface should be the separation of definition (specification and constraint) and Implementation (the principle of separation of name and reality);
• The interface itself reflects the system designer's abstract understanding of the system;
• There shall be two types of interfaces:
  • The first type is the abstraction of an individual, which can correspond to an abstract class;
  • The second is the abstraction of an aspect of an individual, that is, the formation of an abstract interface;
• An individual may have multiple Abstract surfaces, and there are differences between abstract and abstract;

Three oriented differences:

• Object oriented means that when we consider a problem, we take the object as the unit and consider its attributes and methods;
• Process oriented means that when we consider a problem, we consider its implementation in a specific process (transaction process);
• Interface design and non interface design are aimed at reuse technology, which is not a problem with object-oriented (process), but more reflected in the overall architecture of the system;

2. Using annotation development

• Annotations are implemented directly on the interface

    @Select("select * from user")
    List<User> getUserByAnnotation();

• The interface needs to be bound in the core configuration file

    <mappers>
        <mapper class="com.lengzher.dao.UserMapper"/>
    </mappers>

• test

    @Test
    public void getUserByAnnotation(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserByAnnotation();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

• Essence: reflection mechanism implementation
• Bottom layer: dynamic proxy

3. Annotation implementation CRUD

• Set auto commit transactions

    //Set to true to automatically commit transactions
	public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession(true);
    }

• CRUD

  • Interface

  @Select("select * from mybatis.user")
      List<User> getUserByAnnotation();
  
      //Method has multiple parameters. All parameters must be preceded by @ Param ("field name") annotation
      @Select("select * from user where id = #{id}")
      User getUserById(@Param("id")int userId);
  
      @Update("update user set name=#{name},pwd=#{password} where id = #{id}")
      int updateUser(User user);
  
      @Insert("insert into user (id,name,pwd)values(#{id},#{name},#{password})")
      int AddUser(User user);
  
      @Delete("delete from user where id =#{id}")
      int delUser(@Param("id")int id);
  

  • test

      @Test
      public void Test(){
          SqlSession sqlSession = MybatisUtils.getSqlSession();
          UserMapper mapper = sqlSession.getMapper(UserMapper.class);
          //Query user by id
          User userById = mapper.getUserById(2);
          System.out.println(userById);
  
          //Modify user
          int linia = mapper.updateUser(new User(2, "Linia", "1232"));
  
          //Add user
          int add = mapper.AddUser(new User(8,"lengzher","123112"));
  
          //delete user
          int del = mapper.delUser(9);
  
          sqlSession.close();
  
      }
  

  • Tips:

    • Be sure to bind the interface registration to our core configuration file!!

  • About @ Param() annotation

    • Parameters of basic type or String type need to be added
    • The reference type does not need to be added
    • If you need a basic type, you can ignore it, but it is recommended to add it!
    • We refer to the attribute name set in @ Param() in SQL!!!!

  • #The difference between {} and ${}

    • #{} can largely prevent sql injection