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PODiscount strategy in shopping cart and orders
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  1. PODiscount strategy in shopping cart and orders
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    copied!<p>I am trying to implement a system that can handle multiple discounts applied to my cart/completed orders. I have applied a strategy type pattern to encapsulate the processing of the discounts within the discounts. </p> <p>I have come up with the following: an abstract discount base class with subclasses making up the concrete discounts. These are then applied to either an order/cart object and will process the contents of the order/cart when added to the cart/order. </p> <p>Would love some comments on the code attached. Various protected constructors and members marked "virtual" needed for nhibernate.</p> <p>Chev</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using NUnit.Framework; namespace CodeCollective.RaceFace.DiscountEngine { [TestFixture] public class TestAll { #region Tests [Test] public void Can_Add_Items_To_Cart() { Cart cart = LoadCart(); // display the cart contents foreach (LineItem lineItem in cart.LineItems) { Console.WriteLine("Product: {0}\t Price: {1:c}\t Quantity: {2} \t Subtotal: {4:c} \t Discount: {3:c} \t| Discounts Applied: {5}", lineItem.Product.Name, lineItem.Product.Price, lineItem.Quantity, lineItem.DiscountAmount, lineItem.Subtotal, lineItem.Discounts.Count); } } [Test] public void Can_Add_Items_To_An_Order() { // create the cart Order order = new Order(new Member("Chev")); // add items to the cart GenericProduct hat = new GenericProduct("Cap", 110m); order.AddLineItem(hat, 5); EventItem race = new EventItem("Ticket", 90m); order.AddLineItem(race, 1); // add discounts Discount percentageOff = new PercentageOffDiscount("10% off all items", 0.10m); percentageOff.CanBeUsedInJuntionWithOtherDiscounts = false; order.AddDiscount(percentageOff); Discount spendXgetY = new SpendMoreThanXGetYDiscount("Spend more than R100 get 10% off", 100m, 0.1m); spendXgetY.SupercedesOtherDiscounts = true; order.AddDiscount(spendXgetY); Discount buyXGetY = new BuyXGetYFree("Buy 4 hats get 2 hat free", new List&lt;Product&gt; { hat }, 4, 2); buyXGetY.CanBeUsedInJuntionWithOtherDiscounts = false; buyXGetY.SupercedesOtherDiscounts = true; order.AddDiscount(buyXGetY); // display the cart contents foreach (LineItem lineItem in order.LineItems) { Console.WriteLine("Product: {0}\t Price: {1:c}\t Quantity: {2} \t Subtotal: {4:c} \t Discount: {3:c} \t| Discounts Applied: {5}", lineItem.Product.Name, lineItem.Product.Price, lineItem.Quantity, lineItem.DiscountAmount, lineItem.Subtotal, lineItem.Discounts.Count); } } [Test] public void Can_Process_A_Cart_Into_An_Order() { Cart cart = LoadCart(); Order order = ProcessCartToOrder(cart); // display the cart contents foreach (LineItem lineItem in order.LineItems) { Console.WriteLine("Product: {0}\t Price: {1:c}\t Quantity: {2} \t Subtotal: {4:c} \t Discount: {3:c} \t| Discounts Applied: {5}", lineItem.Product.Name, lineItem.Product.Price, lineItem.Quantity, lineItem.DiscountAmount, lineItem.Subtotal, lineItem.Discounts.Count); } } private static Cart LoadCart() { // create the cart Cart cart = new Cart(new Member("Chev")); // add items to the cart GenericProduct hat = new GenericProduct("Cap", 110m); cart.AddLineItem(hat, 5); EventItem race = new EventItem("Ticket", 90m); cart.AddLineItem(race, 1); // add discounts Discount percentageOff = new PercentageOffDiscount("10% off all items", 0.10m); percentageOff.CanBeUsedInJuntionWithOtherDiscounts = false; cart.AddDiscount(percentageOff); Discount spendXgetY = new SpendMoreThanXGetYDiscount("Spend more than R100 get 10% off", 100m, 0.1m); spendXgetY.SupercedesOtherDiscounts = true; cart.AddDiscount(spendXgetY); Discount buyXGetY = new BuyXGetYFree("Buy 4 hats get 2 hat free", new List&lt;Product&gt; { hat }, 4, 2); buyXGetY.CanBeUsedInJuntionWithOtherDiscounts = false; buyXGetY.SupercedesOtherDiscounts = true; cart.AddDiscount(buyXGetY); return cart; } private static Order ProcessCartToOrder(Cart cart) { Order order = new Order(cart.Member); foreach(LineItem lineItem in cart.LineItems) { order.AddLineItem(lineItem.Product, lineItem.Quantity); foreach(Discount discount in lineItem.Discounts) { order.AddDiscount(discount); } } return order; } #endregion } #region Discounts [Serializable] public abstract class Discount : EntityBase { protected internal Discount() { } public Discount(string name) { Name = name; } public virtual bool CanBeUsedInJuntionWithOtherDiscounts { get; set; } public virtual bool SupercedesOtherDiscounts { get; set; } public abstract OrderBase ApplyDiscount(); public virtual OrderBase OrderBase { get; set; } public virtual string Name { get; private set; } } [Serializable] public class PercentageOffDiscount : Discount { protected internal PercentageOffDiscount() { } public PercentageOffDiscount(string name, decimal discountPercentage) : base(name) { DiscountPercentage = discountPercentage; } public override OrderBase ApplyDiscount() { // custom processing foreach (LineItem lineItem in OrderBase.LineItems) { lineItem.DiscountAmount = lineItem.Product.Price * DiscountPercentage; lineItem.AddDiscount(this); } return OrderBase; } public virtual decimal DiscountPercentage { get; set; } } [Serializable] public class BuyXGetYFree : Discount { protected internal BuyXGetYFree() { } public BuyXGetYFree(string name, IList&lt;Product&gt; applicableProducts, int x, int y) : base(name) { ApplicableProducts = applicableProducts; X = x; Y = y; } public override OrderBase ApplyDiscount() { // custom processing foreach (LineItem lineItem in OrderBase.LineItems) { if(ApplicableProducts.Contains(lineItem.Product) &amp;&amp; lineItem.Quantity &gt; X) { lineItem.DiscountAmount += ((lineItem.Quantity / X) * Y) * lineItem.Product.Price; lineItem.AddDiscount(this); } } return OrderBase; } public virtual IList&lt;Product&gt; ApplicableProducts { get; set; } public virtual int X { get; set; } public virtual int Y { get; set; } } [Serializable] public class SpendMoreThanXGetYDiscount : Discount { protected internal SpendMoreThanXGetYDiscount() { } public SpendMoreThanXGetYDiscount(string name, decimal threshold, decimal discountPercentage) : base(name) { Threshold = threshold; DiscountPercentage = discountPercentage; } public override OrderBase ApplyDiscount() { // if the total for the cart/order is more than x apply discount if(OrderBase.GrossTotal &gt; Threshold) { // custom processing foreach (LineItem lineItem in OrderBase.LineItems) { lineItem.DiscountAmount += lineItem.Product.Price * DiscountPercentage; lineItem.AddDiscount(this); } } return OrderBase; } public virtual decimal Threshold { get; set; } public virtual decimal DiscountPercentage { get; set; } } #endregion #region Order [Serializable] public abstract class OrderBase : EntityBase { private IList&lt;LineItem&gt; _LineItems = new List&lt;LineItem&gt;(); private IList&lt;Discount&gt; _Discounts = new List&lt;Discount&gt;(); protected internal OrderBase() { } protected OrderBase(Member member) { Member = member; DateCreated = DateTime.Now; } public virtual Member Member { get; set; } public LineItem AddLineItem(Product product, int quantity) { LineItem lineItem = new LineItem(this, product, quantity); _LineItems.Add(lineItem); return lineItem; } public void AddDiscount(Discount discount) { discount.OrderBase = this; discount.ApplyDiscount(); _Discounts.Add(discount); } public virtual decimal GrossTotal { get { return LineItems .Sum(x =&gt; x.Product.Price * x.Quantity); } } public virtual DateTime DateCreated { get; private set; } public IList&lt;LineItem&gt; LineItems { get { return _LineItems; } } } [Serializable] public class Order : OrderBase { protected internal Order() { } public Order(Member member) : base(member) { } } #endregion #region LineItems [Serializable] public class LineItem : EntityBase { private IList&lt;Discount&gt; _Discounts = new List&lt;Discount&gt;(); protected internal LineItem() { } public LineItem(OrderBase order, Product product, int quantity) { Order = order; Product = product; Quantity = quantity; } public virtual void AddDiscount(Discount discount) { _Discounts.Add(discount); } public virtual OrderBase Order { get; private set; } public virtual Product Product { get; private set; } public virtual int Quantity { get; private set; } public virtual decimal DiscountAmount { get; set; } public virtual decimal Subtotal { get { return (Product.Price*Quantity) - DiscountAmount; } } public virtual IList&lt;Discount&gt; Discounts { get { return _Discounts.ToList().AsReadOnly(); } } } #endregion #region Member [Serializable] public class Member : EntityBase { protected internal Member() { } public Member(string name) { Name = name; } public virtual string Name { get; set; } } #endregion #region Cart [Serializable] public class Cart : OrderBase { protected internal Cart() { } public Cart(Member member) : base(member) { } } #endregion #region Products [Serializable] public abstract class Product : EntityBase { protected internal Product() { } public Product(string name, decimal price) { Name = name; Price = price; } public virtual string Name { get; set; } public virtual decimal Price { get; set; } } // generic product used in most situations for simple products [Serializable] public class GenericProduct : Product { protected internal GenericProduct() { } public GenericProduct(String name, Decimal price) : base(name, price) { } } // custom product with additional properties and methods [Serializable] public class EventItem : Product { protected internal EventItem() { } public EventItem(string name, decimal price) : base(name, price) { } } #endregion #region EntityBase [Serializable] public abstract class EntityBase { private readonly Guid _id; protected EntityBase() : this(GenerateGuidComb()) { } protected EntityBase(Guid id) { _id = id; } public virtual Guid Id { get { return _id; } } private static Guid GenerateGuidComb() { var destinationArray = Guid.NewGuid().ToByteArray(); var time = new DateTime(0x76c, 1, 1); var now = DateTime.Now; var span = new TimeSpan(now.Ticks - time.Ticks); var timeOfDay = now.TimeOfDay; var bytes = BitConverter.GetBytes(span.Days); var array = BitConverter.GetBytes((long)(timeOfDay.TotalMilliseconds / 3.333333)); Array.Reverse(bytes); Array.Reverse(array); Array.Copy(bytes, bytes.Length - 2, destinationArray, destinationArray.Length - 6, 2); Array.Copy(array, array.Length - 4, destinationArray, destinationArray.Length - 4, 4); return new Guid(destinationArray); } public virtual int Version { get; protected set; } #region Equality Tests public override bool Equals(object entity) { return entity != null &amp;&amp; entity is EntityBase &amp;&amp; this == (EntityBase)entity; } public static bool operator ==(EntityBase base1, EntityBase base2) { // check for both null (cast to object or recursive loop) if ((object)base1 == null &amp;&amp; (object)base2 == null) { return true; } // check for either of them == to null if ((object)base1 == null || (object)base2 == null) { return false; } if (base1.Id != base2.Id) { return false; } return true; } public static bool operator !=(EntityBase base1, EntityBase base2) { return (!(base1 == base2)); } public override int GetHashCode() { { return Id.GetHashCode(); } } #endregion #endregion } </code></pre> <p>}</p>
 

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