Today I think of ado.net, which has been useless for a long time. I should forget it when I don't need it, so I wrote a demo, and then defined a data access class library with sqlHelper.cs in it. Then when debugging, it died that the database connection configuration could not be read, but it was clear that there was no problem with the link string. I turned to Du Niang and found this post: https://bbs.csdn.net/topics/120075263 , I just found out [Knock on the blackboard below and focus on it]
Here is my demo directory:
