Back-end drop-down selection automatic judgment

【main body】

   Requirement: Add automatic verification for drop-down selection in the background

  
   Background prompt when no category is selected

【main body】

      Here is the idea. According to the value judgment, set the value of the default display item of article classification to 0. Then add judgment in the automatic detection of the model. Check out the manual here after trying several options. tried

equal verifies that it is equal to a value defined by the previous validation rule
notequal verifies that it is not equal to a value defined by the previous validation rule (new in version 3.1.2)

     But it didn't work, so I changed my mind. Set the default value to empty, and use the function that checks the required fields to verify

array('verify','require','please select the drop-down option'), //By default, regular verification is used