Mapper agent development

Mapper Agent development

Mapper Concept of agent development

We used to write code in a basic way , It also has the problem of hard coding （ Too high coupling ）： as follows
// perform sql list<User>users = sqlSession.selectList("test.selectAll"); System.out.println(users);
This call selectList（） Method pass parameters are in the mapping configuration file namespace.id value . This is not convenient for later maintenance . If you use Mapper The way of agency is as follows , Then the coupling degree can be reduced
//3. Get proxy object UserMapper userMapper = SqlSession.getMapper(UserMapper.class); //4. Execution method , It's actually execution sql sentence List<User>users=userMapper.selectAll();
As can be seen from the above description Mapper The purpose of agency ：
Reduced coupling
Simplify late execution SQL
stay MyBatis The official website is also recommended Mapper Agency mode .

Use Mapper Agency request

Use Mapper Agency mode , The following requirements must be met ：

Definition and SQL Mapping files with the same name Mapper Interface , And will Mapper Interface and SQL The mapping files are placed in the same directory . Here's the picture

Set up SQL Mapping files namespace The attribute is Mapper The interface is fully qualified

<!--
namespace: The name space , Must be the fully qualified name of the corresponding interface 
-->
<mapper namespace="com.itheima.mapper.UserMapper">

stay Mapper Define methods in interfaces , The method name is SQL In the mapping file sql Of the statement id, And keep the parameter type consistent with the return value type