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I have an Entity Framework Project and a repository class in a separate project from my MVC3 web application. I have established a reference in my MVC project to the Entity Framework data project so i can instantiate an instance of the repository and call the methods thereof. However I get the error:

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

I've run into this before and I believe the solution is to include the connection string from the entity framework app.config file in the MVC web.config file.

This doesn't rest well with me. It feels like there should be another way that would make projects less tightly coupled together. I'm I dreaming or is there a better practice that would allow me just to make call to the referenced dll and be done with it?

Thanks

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    You do need to copy the connection string from the EF project's web.config across to the MVC Project web.config. It allows different clients of the EF model to target different databases. Commented Mar 20, 2012 at 12:13
  • The output of a class library is a dll, by definition it is a reusable library. Configuration settings such as a connection string can be embedded in it, however this is not recommended, given that it will make it very hard to be used outside your application. Commented Mar 20, 2012 at 12:22

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The app.config file that is included in the DLL of your Entity Framework project contains a Connection String that is used by the EDMX designer to find the target database when running an 'Update Model from Database' command.

When deploying your application, the only configuration file that is known is the web.config. The app.config file from your EF dll is not used in production.

So in your web.config you include the connection string that is used when you are running your MVC application. When using transformations you can also specify different connection strings for different deployment scenarios (test and production for example).

So it's not like you are introducing some sort of coupling. You are just using the configuration methods that .NET offers you.

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There are ways, hard-coding the connection string in your repository and using it when you create the context comes to mind, but you most certainly don't want to use them. The right way to handle it is through the configuration file. You really don't want to have it use the configuration file from the DLL, since that would give you less control over what connection string you're using. This would make it harder, rather than easier, to have different connection strings for integration testing, staging, and production. While it's possible to combine the approach (fixed connection string that can be overridden by a configuration setting), having used both my preference is for a completely configuration driven approach. I like the single convention and the one-time step of updating the Web.Config (and any transforms) with the correct configuration setting seems little cost to pay for the simple convention of using the configuration always.

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I don't understand how putting a connection string in the MVC project's config file makes it "tightly coupled". The config files themselves are a source for loose coupling. You can always change connection strings using config transforms, meaning you can switch the connection string just by choosing a different solution configuration.

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