c# - ConfigurationManager keeps getting Machine.config connection string

Question

I have a c# assembly that uses the app.config to store its database connection string. When debugging the application I noticed that the connection to the database kept failing because the ConfigurationManager kept returning the machine.config connection string:

data source=.SQLEXPRESS; Integrated Security;....

I added <clear/> before my connection string in the app.config and it fixed the issue on my dev machine. The problem returned when I deployed it to production. Can someone tell me how I can stop the machine.config connection string from being used?

SqlConnection connection = new SqlConnection(ConfigurationManager.ConnectionStrings[0].ConnectionString);

<connectionStrings>
    <clear/>
    <add name="VersionConnectionString"
     connectionString=" Data Source=localhost;Initial Catalog=VersionInfo;User ID=user;Password=password"         
     providerName="System.Data.SqlClient" />
  </connectionStrings>

UPDATE

The following still gives me the machine.config connection string?!

 Configuration appConfig = ConfigurationManager.OpenExeConfiguration(Assembly.GetExecutingAssembly().Location);
                string dllConfigData =
                    appConfig.ConnectionStrings.ConnectionStrings[0].ConnectionString;

Answer 1

When using connection strings in a DLL, you need to add them to your exe's app.config as well, using the exact same name for the setting. Then, you can change the connection string in the exe's .config file and the DLL will pick it up automatically when loaded.

This is probably the only way you can have working custom connection strings in the app.config file when your DB persistence layer is implemented in a separate DLL. Don't even ask me how much time it took me to research and debug this.