How to Correctly Connect to an MDF Database File in C#?

Connecting to MDF Database File in C#

Connecting to a Microsoft Data Format (MDF) database file in C# can present challenges for first-timers. One common issue is encountering an invalid connection string syntax.

Error Encountered

When attempting to connect to an MDF database using the following code:

con.ConnectionString = "DataSource=.\SQLEXPRESS; AttachDbFilename =SampleDatabase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";

An exception is thrown with the message:

System.ArgumentException: Keyword not supported: 'datasource'.

Solution

The error originates from a missing space between "Data" and "Source" in the connection string. To resolve it, modify the connection string as follows:

con.ConnectionString = @"Data Source=.\SQLEXPRESS;
                          AttachDbFilename=c:\folder\SampleDatabase.mdf;
                          Integrated Security=True;
                          Connect Timeout=30;
                          User Instance=True";

Additional Considerations

• Ensure the MDF file is located in the specified location.
• Verify that the SQLEXPRESS instance is running.
• If using a database password, specify it in the connection string.
• Use Visual Studio 2010's Server Explorer to verify the connection.

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