Why Does My C# MDF Database Connection Fail with an ArgumentException on 'DataSource'?

MDF Database Connection Challenges

Connecting to an MDF database file from a C# application can present challenges, especially for beginners. In this article, we will address a common issue encountered when attempting to establish a connection, as exemplified by the code provided.

Error: ArgumentException with 'DataSource' Keyword

When defining the connection string, the code initially contained a "DataSource" keyword. However, this keyword is incorrect.

Solution: Space between "Data" and "Source"

The correct connection string requires a space between "Data" and "Source." The updated code below rectifies this issue:

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

Additional Considerations

• Ensure that the path to the MDF file is correct.
• If the MDF file is encrypted, provide the appropriate encryption password in the connection string.
• Make sure that the SQL Server Express service is running and has access to the MDF file location.

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