Workaround to get the database connection string that is not in app. Config

Today, I added a reference to the database connection string for the app. config file in my own class library, but the return was null, wondering. And then found the answer on the internet originally my app. config file was added to the wrong place, should be added to the startup project, rather than add in the reference project. So I summed up:

The configuration file should be placed inside the main project (startup project) instead of referencing the project.