How to Specify SQL Express MDF File Location Relatively in .NET Applications?

SQL Express Connection String: Specifying MDF File Location Relative to Application

When working with SQL Express databases in C# unit tests, it can be inconvenient to specify the absolute file path to the MDF file in the connection string. Instead, you may prefer to use a relative path or variable.

.NET Core Web Applications:

In web applications using .NET Core, you can leverage the DataDirectory variable to dynamically reference the application's data directory. This directory is typically located at wwwrootApp_Data by default. You can configure the connection string in appsettings.json as follows:

{
  "ConnectionStrings": {
    "MyConnectionString": "Server=.\SQLExpress;AttachDbFilename=|DataDirectory|\MyDatabase.mdf;Database=MyDatabaseForTesting;Trusted_Connection=Yes"
  }
}

.NET Core Desktop Applications:

For desktop applications in .NET Core, the DataDirectory variable is not supported. Instead, you can set the DataDirectory property in the unit test fixture or setup method:

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

    // Rest of initialization logic
}

With this setup, you can specify the connection string in appsettings.json using the DataDirectory variable:

{
  "ConnectionStrings": {
    "MyConnectionString": "Server=.\SQLExpress;AttachDbFilename=|DataDirectory|\MyDatabase.mdf;Database=MyDatabaseForTesting;Trusted_Connection=Yes"
  }
}

In both cases, ensure that the Databases directory is included in the project and that it contains the necessary MDF file.

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