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Using Entity Framework app.config how to switch between environments Dev, Stage and Production

I have a windows application accessing Dev database using DataModel.edmx and it works fine. To access stage environment database I have added another StageDataModel.edmx. So there are two connection strings in app.config:
and
How do I switch between databases in app.config based on environment?
Thanks in advance!

Normally it should be the other way around - create one EF edmx model and two (or more) configuration files for every environment.
At my work, we have three environments:
Release = Production
Stage = before GO live (copy of production, final tests)
Debug = new development, dev team tests
For the three environments, we have three databases, that are (almost) similiar to each other. We create our model from the DEV database. Every project that communicates with the database has always three connection strings with different credentials.
In order to achieve this, you need to:
1) create different build platforms using the Visual Studio configuration manager (in my example, there are three build configurations - Dev/Stage/Release):
2) extract the connection string configuration from the app.settings file. Instead of specifying the connection in the app.settings file, use the configSource parameter like this (the app.config looks like this):
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings configSource="App.ConnectionStrings.Config" />
</configuration>
3) now create different files for every build configuration, named after each build configuration (the wording must be exact!) and containing different servers or databases
App.ConnectionStrings.Debug.config
App.ConnectionStrings.Stage.config
App.ConnectionStrings.Release.config
Foer example the Debug can look like this:
<?xml version="1.0" encoding="utf-8" ?>
<connectionStrings>
<add name="Named.ConnectionString"
connectionString="metadata=res://*/Abstraction.DbDataContext.csdl|res://*/Abstraction.DbDataContext.ssdl|res://*/Abstraction.DbDataContext.msl;provider=System.Data.SqlClient;provider connection string="data source=sql.server.address;initial catalog=People;integrated security=False;user id=DbUser;password=DbPassword;multipleactiveresultsets=True;App=EntityFramework""
providerName="System.Data.EntityClient" />
</connectionStrings>
4) now open your project settings in Visual Studio, go to Build Events and in the Post-Build event command line tell Visual Studio to take on every build the file named after the currently selected build platform and copy it with the specified (in the app.config) name to the output directory:
copy $(ProjectDir)\App.ConnectionStrings.$(ConfigurationName).config $(TargetDir)App.ConnectionStrings.config
Now when you build and start your application, the configuration depends on the build configuration, so you can even debug your application connected to the LIVE environment (when the currently chosen build configuration is Release).
More info on how to use external configuration files and connection strings, can be found in this MSDN article.
A good Entity Framework quick start.

I think you are asking how to use different app.config files for debug/release.
Just name them app.Release.config or app.Debug.config and have the debug or release settings in either one.
If its more complicated than that, you can install a tool such as SlowCheetah to modify XML files, you just need to set up different build configurations.

web.config, app.config priority / dependancies and usage on compilation

Just a quick question. I have a solution splitted in multiple projects. In one project, I have the database interactions and my EDMX. In this project, I have my app.config file with some connections strings.
This project, is imported as dependancy in a Web project. In this one, I have my Web.config where are defined (or "overriden") connections strings.
I'd like to know what are the mechanisms used to configure the database connection. From what I understood, the Web.config has all priority over App.config. But what I'm wondering is, is the App.config in dependancies projects used at compilation time ?
For instance :
Project A => app.config :
<connectionStrings>
<add name="A" connectionString="myConnectionStringA"/>
<add name="B" connectionString="myConnectionStringB"/>
</connectionStrings>
And the same in Web.config but with :
<connectionStrings>
<add name="A" connectionString="myConnectionStringC"/>
<add name="B" connectionString="myConnectionStringD"/>
</connectionStrings>
Which one will be used to define the connection to the EDMX ? In one hand, at compile time, logically it would be A & B used to define it, and C & D would be used at runtime.
But i'm not sure about it and for me, once the dll is "configured", I don't see how can C and D be used instead of A & B.
Could someone explain it to me please ?
Thanks !

The config file that is used at runtime is the one related to where you are launching your application. If you launch the projectA it will be the App.config file.
Actually it will be the file generated by the compilation on the proper directory "Debug" or "Release"
When you run your web project it will be the Web.config file there.
The dll isn't "configured" with the values from the config file, they are read when the application starts running and this will depend on the application that is running.
That is why if you change the values they will change when you relaunch the application without any need to recompile the project.

When designing your entities in Visual Studio, the connection string that is stored in the app.config file of the project is used.
Even though you add a reference to the project from the web project, the app.config of the referenced project is not used at all in the context of the web project. Of course, it can be used as a blueprint when adding the connection strings to the web.config.
The config file that is relevant to the web project is the web.config. So when running or publishing the web project, the settings that are used are the ones in the web.config.
They do not override the settings of the app.config in the sense of a fallback like "if the connection string is not configured in the web.config file, then I use the ones stored in app.config".
It is required that you add the connection strings that you want to use when running the web project to the web.config file, otherwise you'd encounter an error if you used the Entity classes.
For details on configuring ASP.NET web applications, see this link.

But i'm not sure about it and for me, once the dll is "configured", I
don't see how can C and D be used instead of A & B.
The config values are fetched when the progam is running, not when it is compiled.

Entity Framework connections strings messing up app.config

I'm using Entity Framework inside a DLL.
VS creates a app.config, but when I run the application I receive this exception.
"The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid."

You need to include that connection string in the start up project of your solution. If it is a Asp.Net WebForms/MVC application include that connection string in the Web.Config file or if it is a Windows or Console App include it in App.Config file.

How to read values from App.config in .Net 4.0 using configurationManager?

I am creating a windows service in .Net 4.0 and testing some functions of said service with a windows forms client by referencing the service project.
The service project has an App.config file and that file looks like this:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<clear />
<add name="myLocalMySQLDBUsername" connectionString="username"/>
</connectionStrings>
</configuration>
When a function belonging to the service calls:
ConfigurationManager.ConnectionStrings("myLocalMySQLDBUsername").ConnectionString
a null reference error is thrown because my connection string is not loaded. The only connectionStrings that are loaded are from the machine.config file located in c:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Config\machine.config
If I create an application scope setting for the service, I can get that setting by using the My.Settings.setting -> so it's not like the App.config file is not being read.
My question is: why are my connectionStrings not being loaded from the App.config file?
Thank you for your help.
UPDATE:
Also, at this point, even a work around would be appreciated; the only reason for using app.config is to be able to encrypt the contents using the DpapiProtectedConfigurationProvider (the contents will have some username/password values for service and database connections).
I tried creating an AppSettings section manually in the app.config but those settings were also not read by the configurationManager (count = 0).
UPDATE 2:
Per a suggestion, I tried to manually open the app.config file like so:
Dim exePath As String = System.IO.Path.Combine(Environment.CurrentDirectory, "ServiceName.exe")
Dim myConfig As Configuration = ConfigurationManager.OpenExeConfiguration(exePath)
So here is the weird part, when I look inside, path is correct (points to my app.config) but the connectionStrings are still being loaded from the machine.config file (my connectionStrings are not loaded)!! ARGH
UPDATE 3:
Okay, so, I figured it out. When referencing a project(parent) from another project(child), the child's app.config is used even if the parent's classes are being used. Thus, I can get the connectionStrings to show up if I copy them over to the child's app.config. When trying to open it manually, my currentDirectory was of the child, not the parent (strange how it did not throw an exception - it wouldn't have been able to find the config file ... it just silently used the machine.config ... oh well).
Thanks all for the help!

The first thing you'll want to do is make sure that the service account has access to the file (if not running as SYSTEM). It sounds like it should be ok though since you mention My.Settings.Setting works.
The other thing to look out for is to make sure that the app.config has the name of the service executable in it - so if the service exe is MyService.exe the app.config must be named MyService.exe.config.
The last thing to make note of: libraries will read from the executable's app.config that loads the library, not the app.config that is with the library. So if you have a project for the service executable MyService and a project for the library MyServiceLibrary the code in the library will read the app.config from MyService not MyServiceLibrary.

I saw some people say this problem might be fixed by manually re-adding a reference to System.Configuration.dll
SIDE NOTE: If that really is you whole app.config file and not just a snippet then that is your problem... you're app.config file should be MUCH more complicated or .NET will not be able to load it.
WORK AROUND: Use the configuration manager to open this config file (there is an API for that.) You can't get it to load auto-magically just tell the config manager to open it.
I still think the problem is your config file is invalid -- could you please post the FULL file?

Make sure the config file is deployed to the same folder as the executable file, and that it's called your.assembly.exe.config.

I had a similar problem, but in my case it was because I had changed the project's namespace. This is also used as the application settings section element name in the config file, so the code was not finding the new section name. Fiddling with one of the custom setting's values in the project properties and rebuilding caused the new section to written into the app.config alongside the old ones which was what indicated the issue to me.

Error reached after genereated entity framework classes by edmgen tool

First I read this question, but this knowledge did not help to solve my problems.
In initial I've created edmx file by Visual Studio. Generated files with names:
uqsModel.Designer.cs
uqsModel.edmx
This files are located on App_Code folder.
And my web app work normally.
In Web Config generated connectionstring automatically.
<add name="uqsEntities" connectionString="metadata=res://*/App_Code.uqsModel.csdl|res://*/App_Code.uqsModel.ssdl|res://*/App_Code.uqsModel.msl;provider=System.Data.SqlClient;provider connection string="Data Source=aemloviji\sqlexpress;Initial Catalog=uqs;Integrated Security=True;MultipleActiveResultSets=True"" providerName="System.Data.EntityClient" /></connectionStrings>
Then I had to generate classes by the instrument edmgen tool(full generation mode).
Generated new files with names:
uqsModel.cs
uqsModel.csdl
uqsModel.msl
uqsModel.ssdl
uqsViews.cs
it save new classed to the folder where edmx files located before, and remove existing edmx files. And when page redirrects to any web page server side code fails.
And problem: Unable to load the specified metadata resource.
Some idea, please.

The problem seems to be associated with the fact that you have generated metadata in the form of .csdl, .ssdl, and .msl files, and your connection string points to the resource that should be embedded to the project dll (which is likely to be unavailable in your Web Site).
The solution is to correct the path to metadata like the following:
metadata=~\App_Code\uqsModel.csdl|~\App_Code\uqsModel.ssdl|~\App_Code\uqsModel.msl
More information is available here.