public IEnumerable<Onion> ProduceOnions(FactoryId factoryId, OnionQuantity quanity)
        {
            var produceOnions = this.onionDomainService.ProduceOnions(quanity);

            this.factoryDomainService.AssignProducedOnions(factoryId, produceOnions);

            return produceOnions;
        }
        public IReadOnlyCollection<Onion> ProduceOnions(OnionQuantity quantity)
        {
            var onions = Enumerable.Range(0, quantity).Select(i => new Onion()).ToList();

            foreach (var onion in onions)
            {
                this.repository.Save(onion);
            }

            return new ReadOnlyCollection<Onion>(onions);
        }