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Asked: 2026-05-16T15:45:14+00:00

I have a class library that contains a valid connectionString inside the app.config. Inside

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I have a class library that contains a valid connectionString inside the app.config. Inside that class library I want to use it with

ConfigurationManager.ConnectionStrings["NAME"].ConnectionString

My ASP.net 4.0 framework application references that DDL and retrieves data from it. I want create a Entity Framework 4 DataContext within my DDL with the ConnectionString from the App.config. (I do not want to pass the connectionString from my ASP.net application in every single method. (I’m using ObjectDataSources))

However, this line inside my DLL throws a NullReferenceException.

ConfigurationManager.ConnectionStrings["NAME"].ConnectionString

How can I fix this issue?

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1 Answer

  1. Editorial Team

    I have a class library that contains a
    valid connectionString inside the
    app.config

    A class library doesn’t have an app.config file associated. It’s the application consuming this assembly that does. So you need to put the connection string inside this config file (if this is an ASP.NET application this would be web.config). Thus adding an App.config file in a project of type class library in Visual Studio makes no sense.

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