How to Configure a Relative MDF File Path in SQL Express Connection Strings for C# Unit Tests?

SQL Express Connection String: Configuring Relative MDF File Location within Application

When working with SQL Express databases in C# unit test projects, it is inconvenient to define the connection string in an absolute path format. This article explores different approaches to specify the relative location of the database mdf file within the application's configuration.

One consideration is |DataDirectory|, which is typically used in web applications. However, for desktop applications, it is necessary to manually set the |DataDirectory| property in the unit test class. This allows the connection string to include |DataDirectory| as a variable, effectively pointing to the relative MDF file location.

Here's an example demonstrating this approach:

In the app.config file:

<add name="MyConnectionString"
    connectionString="Server=.\SQLExpress;AttachDbFilename=|DataDirectory|\MyDatabase.mdf;Database=MyDatabaseForTesting;Trusted_Connection=Yes;" />

In the unit test class, set the |DataDirectory| property:

[TestInitialize]
public void TestInitialize()
{
    AppDomain.CurrentDomain.SetData("DataDirectory", System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Databases"));

    // Rest of test initialization goes here...
}

This method dynamically sets the DataDirectory to the desired relative path within the application. This allows the connection string to refer to the MDF file in a flexible manner that can be easily modified in different environments.

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