public static void EfSave <T>(this DbContext context, IList <T> entities, Expression <Func <T, object> > pivotKey = null, bool doNotUpdateIfExists = false) where T : class
        {
            EfSaveEngine <T> efSaveEngine = new EfSaveEngine <T>(context, pivotKey);

            efSaveEngine.Save(entities, doNotUpdateIfExists);
        }
        public static void EfSave <T>(this DbContext context, IList <T> entities, Expression <Func <T, object> > pivotKey = null) where T : class
        {
            EfSaveEngine <T> efSaveEngine = new EfSaveEngine <T>(context, pivotKey);

            efSaveEngine.Save(entities);
        }