Moving Entity Framework model into class library from web project

Question

I am using Entity Framework and recently came to realize the benefits of having your EF model in another project within the same solution so that I can build multiple UIs from it.

I moved it over to a new class library project and updated all the references to the entities in the web project to use the new dll generated by the project. Everything has gone smoothly, except for one small snag. When I moved EF over to the new project, somehow it was still reading its connection string from the web.config in the web project (don't ask me how because I have no clue).

I used "Update Model from Database" in the EF designer and it did not find a connection string (as I expected after moving it over to the new project) so I used the wizard to generate a new connection string, which it did just fine. The new connection string now resides in App.config within the class library project. The connection string in the properties window is correct now, and the designer is reading it from the App.Config. I went ahead and deleted the connection string from Web.Config in the web project.

Now when running the application I get the following error:

The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid.

If I paste the connection string back into the Web.Config it all works just fine. I do not want to create a new EF model from scratch because it is a fairly complicated model and I did a lot of restructuring after pulling in from the DB. I have poured over the generated CS file as well as the XML in the edmx file and cannot find anything useful. Any help is much appreciated. Obviously for now, until I figure this out, I'm just leaving the connection string in web.config since, for whatever reason, that seems to work.

Answer 1

This is by design; while the config file in the class library is what the designer will use, the configuration file of the actual application is what will get used at runtime. Whether that's Web.config for an ASP.NET project or App.config for a Winforms or WPF project, it's the application configuration file (or something higher up, like Machine.config) that will be used; the file in the class library is not part of the application.

If you're trying to provide an EF model that will work without having to specify the connection string in the application or web configuration file, then you'll have to store the connection string some other way (you could always hard-code it) and pass it into the appropriate overload of your context's constructor.

My solution is generally to provide a static parameterless function on the context itself that calls this overload with the appropriate connection string.