You have to implement the ICTMSEntitiesContext
in the CTMSEntitiesModel
class. Otherwise there is no way to cast an instance of the class to the target interface.
Given that you are using OpenAccess and the fact that the context class may be automatically generated I would suggest to you add the interface implementation into a new partial class in different project file to avoid losing the custom code after the original file is regenerated:
public partial class CTMSEntitiesModel : ICTMSEntitiesContext
{
// FetchStrategy property is already defined
}