resultType statementreturns the full class name or alias of the value type

• resultType returns a map set, key is the column name, and value is the corresponding value

Using resultMap to realize joint table query

• A mapping relationship is established between the resultMap query result set and the java Bean
  • Multi table query sql statement

    SELECT su.*,r.rolename FROM sys_user su,"role" r WHERE su.roleid =r.id AND r.id =1;

  • Result set of query
    
• Establish a mapping relationship between the result set and the entity class, and add the fields to be displayed in the User entity class, rolename and roleid
  
• Use resultMap to establish the data to be displayed. property represents the attribute of the entity class and column represents the field of the table
  
• Test class
  
• console output
  

Note: the method in dao layer interface must correspond to the sql statement in mapper file. For example, the following error

• junit reported the following error
  
• console output

The reason is that the method is written in the RoleMapper interface and the sql statement is not written in the corresponding xml file

• RoleMapper.java
  
• RoleMapper.xml
  
• When the column name of the database is different from the entity class, you need to use resultMap mapping
• resultMap is also required for association mapping during joint query

Configure the log implementation of mybatis as log4j2, and sql statements will be printed during background printing and output

• Use association to associate Java beans to realize query

  • When an entity class is an attribute of another entity class, such as:
    
• Use the sub attribute association of resultMap to implement
  
• You can also write a resultMap separately and reference it in the association, such as:
  
• The test results are the same
  
• When a collection exists in an entity class
  
• Use the collection in the resultMap to associate the implementation
  
• Test class
  
• test result
  

The required data is displayed in resultmap, association and collection, and the unnecessary data can not be displayed