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LocalDb error: Cannot attach the file ‘sample.mdf’ as database ‘sample.mdf’

In a demo app I  used the LocalDB functionality to host my database files. This should have saved me some time. However when I ran the application, I ended up with the following error message:

{"Cannot attach the file 'C:\\Projects\\SampleApp\\App_Data\\sample.mdf' as database 'sample'."}

Looking at my connection string data inside my web.config, everything looked fine:

<add name="DefaultConnection" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=Sample;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\Sample.mdf" providerName="System.Data.SqlClient" />

But when I opened up the App_Data folder, I found an empty folder. Aha! It seems like you have to create the database file yourself. I opened up the solution, right clicked on the App_Data folder and choose Add –> New item…

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