When attaching a SQL Express DB via a connection string, is it an exclusive lock?

Question

In .NET, you can open a SQL Express database simply by attaching the database MDF file in the connection string (that is, you don't have to have any server software installed, it just attaches to the MDF file on the fly).

When an application does this, does it obtain an exclusive lock on the database file? Or, can a second application also attach to and open the MDF file in this same way, and query the database while program #1 is using it?

Answer 1

You are correct, only a single connection can be open to the MDF at a time.

This can get really annoying when you open the database through your server explorer in Visual Studio, and then try to run your application.

I've caught myself doing that too many times to count, and I always invariably end up just attaching the mdf to my sql server instance.