The process cannot access the file 'C:Project\App_Data\Database.mdf' because it is being used by another process

I'm getting the following error:

The process cannot access the file 'C:Project\App_Data\Database.mdf' because it is开发者_JAVA百科 being used by another process.

How can I solve it?

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It's used by another process, maybe from SQL Server service.
You could use Unlocker to find which process and take appropriate action.
Be careful: if'you re using VS, you could have opened a db connection during development.