eShopOnContainers/src/Services/Ordering/Ordering.Domain/AggregatesModel/OrderAggregate/Order.cs

using Microsoft.eShopOnContainers.Services.Ordering.Domain.AggregatesModel.BuyerAggregate;
using Microsoft.eShopOnContainers.Services.Ordering.Domain.Seedwork;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Microsoft.eShopOnContainers.Services.Ordering.Domain.AggregatesModel.OrderAggregate
{
    public class Order
        : Entity
    {
        // DDD Patterns comment
        // Using private fields, allowed since EF Core 1.1, is a much better encapsulation
        // aligned with DDD Aggregates and Domain Entities (Instead of properties and property collections)
        private DateTime _orderDate;

        //TO DO: These fields need to be converted to a VALUE-OBJECT "Address" 
        private string _street;
        private string _city;
        private string _state;
        private string _country;
        private string _zipCode;

        public Buyer Buyer { get; private set; }
        private int _buyerId;

        public OrderStatus OrderStatus { get; private set; }
        private int _orderStatusId;

        // DDD Patterns comment
        // Using a private collection field, better for DDD Aggregate's encapsulation
        // so OrderItems cannot be added from "outside the AggregateRoot" directly to the collection,
        // but only through the method OrderAggrergateRoot.AddOrderItem() which includes behaviour.
        private readonly HashSet<OrderItem> _orderItems;

        //TODO: Use List<> instead of HashSet<> because of the comment below
        // So we won't need the ".ToList()"

        public IEnumerable<OrderItem> OrderItems => _orderItems.ToList().AsReadOnly();
        // Using List<>.AsReadOnly() 
        //This will create a read only wrapper around the private list.
        //It's much cheaper than .ToList() because it will not have to copy all items in a new collection. (Just one heap alloc for the wrapper instance)
        //https://msdn.microsoft.com/en-us/library/e78dcd75(v=vs.110).aspx 

        public PaymentMethod PaymentMethod { get; private set; }
        private int _paymentMethodId;

        protected Order() { }

        public Order(int buyerId, int paymentMethodId, Address address)
        {

            _buyerId = buyerId;
            _paymentMethodId = paymentMethodId;
            _orderStatusId = OrderStatus.InProcess.Id;
            _orderDate = DateTime.UtcNow;
            _street = address.Street;
            _city = address.City;
            _state = address.State;
            _country = address.Country;
            _zipCode = address.ZipCode;

            _orderItems = new HashSet<OrderItem>();
        }

        // DDD Patterns comment
        // This Order AggregateRoot's method "AddOrderitem()" should be the only way to add Items to the Order,
        // so any behavior (discounts, etc.) and validations are controlled by the AggregateRoot 
        // in order to maintain consistency between the whole Aggregate. 
        public void AddOrderItem(int productId, string productName, decimal unitPrice, decimal discount, string pictureUrl, int units = 1)
        {
            var existingOrderForProduct = _orderItems.Where(o => o.ProductId == productId)
                .SingleOrDefault();

            if (existingOrderForProduct != null)
            {
                //if previous line exist modify it with higher discount  and units..

                if (discount > existingOrderForProduct.GetCurrentDiscount())
                {
                    existingOrderForProduct.SetNewDiscount(discount);
                    existingOrderForProduct.AddUnits(units);
                }
            }
            else
            {
                //add validated new order item

                var orderItem = new OrderItem(productId, productName, unitPrice, discount, pictureUrl, units);

                _orderItems.Add(orderItem);
            }
        }
    }
}