How to fix “The ConnectionString property has not been initialized”

Question

When I start my application I get: The ConnectionString property has not been initialized.

Web.config:

Answer 1

I stumbled in the same problem while working on a web api Asp Net Core project. I followed the suggestion to change the reference in my code to:

ConfigurationManager.ConnectionStrings["NameOfTheConnectionString"].ConnectionString

but adding the reference to System.Configuration.dll caused the error "Reference not valid or not supported".

To fix the problem I had to download the package System.Configuration.ConfigurationManager using NuGet (Tools -> Nuget Package-> Manage Nuget packages for the solution)