[ADO.NET] What's the deal with |Pipe-delimited| variables in connection strings?

Question

I know that |DataDirectory| will resolve to App_Data in an ASP.NET application but is that hard-coded or is there a generalized mechanism at work along the lines of %environment variables%?

Answer 1

From the MSDN Smart Client Data Blog:

In this version, the .NET runtime added support for what we call the DataDirectory macro. This allows Visual Studio to put a special variable in the connection string that will be expanded at run-time...

By default, the |DataDirectory| variable will be expanded as follow:

• For applications placed in a directory on the user machine, this will be the app's (.exe) folder.
• For apps running under ClickOnce, this will be a special data folder created by ClickOnce
• For Web apps, this will be the App_Data folder

Under the hood, the value for |DataDirectory| simply comes from a property on the app domain. It is possible to change that value and override the default behavior by doing this:

AppDomain.CurrentDomain.SetData("DataDirectory", newpath)