The specified named connection is either not found in the configuration, not intended to be used with the EntityClient provider, or not valid
要么是没有发现在配置中，指定的命名连接，不打算要用于EntityClient提供程序，或不是有效的
解决办法：
I suspect that your issue is coming from the fact that you have more than one project in your solution and the one that contains your entity framework stuff including edmx files is NOT the solutions's startup project. In this case even if the connection string exists in the EF app.config project, still CLR cannot find it at runtime. For example if you have a web site and a EF project in your solution, you need to copy the connection string from the EF project's app.config to your website's web.config. Basically any connection string data should be exist in the config file of the project that the .Net threads initiated from by CLR (i.e. your startup project). If this is not your case, then just open your edmx file, right click on its surface, select properties and copy the connection string and paste it into your app.config Connection String section. This way you can make sure that you are having the correct one in your config.