If you are deploying the database with the application, the proper way to go about this is to add the data file to the project and set its Copy to output directory
to Copy if newer
, then use "|DataDirectory|"
in your connection string as the folder path. That will automatically resolve to the correct folder no matter where the application is deployed as well as when running in the debugger. See www.connectionstrings.com for some examples.
Note that, for most deployed applications, the data directory defaults to the program folder. This means that the advice above is like using Application.StartupPath
in a WinForms app but you don't have to use code to set it. If you use ClickOnce deployment then the data directory is managed by ClickOnce and the connection string is resolved automatically still. For Web Forms apps, it resolves to the App_Data folder. Not sure what happens for more modern web apps as I've never tried it.