ConnectionString from app.config of a DLL is null

Question

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?

Answer 1

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.

Answer 2

在这种情况下，您将相同的<connectionStrings>条目 （有问题的<add> ）放在Web应用程序的web.config ， ConfigurationManager.ConnectionStrings始终查看当前配置，这是您的案例中的web.config。

Answer 3

In case if you don't waana use ConfigurationManager

If i assume the config file is mydll.dll.config i can load it as XElement and parse it using Linq as

var xe = XElement.Load("mydll.dll.config");
var connectionString = xe.Descendants("connectionStrings")
     .Elements("add")
     .FirstOrDefault(a => a.Attribute("name").Value == Name)
     .Attribute("connectionString").Value;

where Name is the connectionString name in the XML. Without using the ConfigurationManager import and other stuffs. The only requirement for this to make sure that the config file sit next to the dll.