Question

Whenever I try to run anything in my C# code I get the following error:

System.InvalidOperationException was unhandled by user code
Message=No connection string configured

and it happens in the following code.

if (System.Configuration.ConfigurationManager.ConnectionStrings["DBContext"] == null)
{
     throw new System.InvalidOperationException("No connection string configured");
}

connectionString = string.Format("{0};Application Name={1}", System.Configuration.ConfigurationManager.ConnectionStrings["DBContext"].ConnectionString, this.applicationName);

So System.Configuration.ConfigurationManager.ConnectionStrings["DBContext"] is null. I can’t really find anything about it, one question that might be related: How to fix "The ConnectionString property has not been initialized" suggests that something might be wrong with the config file. At this moment I’m afraid I somehow accidentally deleted a config file.

Also, just read this in the documentation:

Returns a ConnectionStringSettingsCollection object that contains the contents of the ConnectionStringsSection object for the current application's default configuration. 

It contains the default values, so I’m inclined it’s in a config file that I must have accidentally removed.

If I’m right, I don’t know which one or where it should be, and what it should contain. If I’m wrong, I have no clue where it comes from.
So where is the System.Configuration.ConfigurationManager.ConnectionStrings[“DBContext”] set? And/or how can I fix this issue?

Answer 1

Connection strings in .NET come from a config file – either app.config for console / Windows apps or web.config for a Web app.

You can add a new config file to your project by right-clicking the project and adding the correct file, and make sure you have the following section in that config file:

<configuration>
  <connectionStrings>
    <add name="DBContext" connectionString="data source=.\SQLEXPRESS;Initial Catalog=databasename;Integrated Security=SSPI" providerName="System.Data.SqlClient" />
  </connectionStrings>
  ...
</configuration>

And of course you’d need to replace the connection string with something that is appropriate for your environment (e.g. replace databasename with your database name).