hrdev | Hex-Rays Decompiler Enhanced View | Plugin library

tldr: That connection is not attached to your project.

The connection you can see is just a useful view of the database in your server explorer. It's a GUI tool for your convenience, instead of having to switch to SSMS. It's part of visual studio, not part of the application you are writing. Your code knows nothing about it.

Your application must still connect to the database in the normal way using a connection string when it is executing.

This is because your application executes separately from Visual Studio. Think about it...when you deploy your code to be a live application, it no longer has any link to Visual Studio. It's out there on its own. So it would make no sense for it to depend on a component inside Visual Studio. You may be using GUI tools to drag things like datasets into your application, but all that is doing is providing a graphical way to auto-generate some code. In the end that code must still be able to execute independently.

The Dataset editor you mentioned is another design-time tool. So yes it can connect to the database via the Connection object in Server Explorer, but that has nothing to do with your application, because the application does not execute the designer code when it runs. Instead it uses the dataset created by it (i.e. the result of using the designer) as part of the application. That dataset, in the context of your running application, needs to connect again to the database in order to fill with data. It does that using the standard connection string in your config file.

Summary:

Don't confuse the tools you're using the build the application with the actual finished application itself. All that these tools do is make it easier to write and generate your application's code. You could write exactly the same application completely by hand using Notepad, if you wanted to. And you could compile and execute it using command-line tools, without any need for Visual Studio.