void replaceListInDB <T>(ICollection <T> listToInsert, ICollection <T> listToReplace, IEqualityComparer <T> comparer)
        {
            var substraction = listToReplace.Except(listToInsert, comparer).ToList();

            foreach (var i in substraction)
            {
                _context.Remove(i);
            }
            foreach (var i in listToInsert)
            {
                /*try
                 * {*/
                _context.Add(i);

                /*}
                 * catch (InvalidOperationException e)
                 * {
                 *  _context.Update(i);
                 * }*/
            }
        }