ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded

The Entity Framework provider type 'System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer' registered in the application config file for the ADO.NET provider with invariant name 'System.Data.SqlClient' could not be loaded. Make sure that the assembly-qualified name is used and that the assembly is available to the running application. See http://go.microsoft.com/fwlink/?LinkId=260882 for more information.

　　出现问题的原因：缺少dll的引用，在引用EF类库时，如果只引用EntityFramework不引用EntityFramework.SqlServer的话就会遇到这样的错误，所以这个问题的解决方案就是：添加对 EntityFramework.SqlServer.dll 的引用即可