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