e.g. 5.27 Using LINQ to Query Data

e.g. 5.22 Extending the Filtering Expression by Lambda

chap5_essential_language_features/essential_csharp_features/Program.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 using automatically_implemented_properties;
 
 namespace automatically_implemented_properties
@@ -9,35 +10,70 @@ namespace automatically_implemented_properties
     {
         static void Main(string[] args)
         {
-            // create and populate Shopping Cart
+            Product[] products =
-            ShoppingCart cart = new ShoppingCart
             {
-                Products = new List<Product>
+                new Product {Name = "Kayak", Category = "Watersports", Price = 275M},
-                {
+                new Product {Name = "Lifejacket", Category = "Watersports", Price = 48.95M},
-                    new Product {Name = "Kayak", Price = 275M},
+                new Product {Name = "Soccer ball", Category = "Soccer", Price = 19.50M},
-                    new Product {Name = "Lifejacket", Price = 48.95M},
+                new Product {Name = "Corner flag", Category = "Soccer", Price = 34.95M}
-                    new Product {Name = "Soccer ball", Price = 19.50M},
-                    new Product {Name = "Corner flag", Price = 34.95M}
-                }
             };
-            // get total value of the products in cart
+
-            decimal cartTotal = cart.TotalPrices();
+            var results = from product in products
-            
+                orderby product.Price descending
-            Console.WriteLine("Total: {0:c}", cartTotal);
+                select new
+                {
+                    product.Name,
+                    product.Price
+                };
+
+            int count = 0;
+            // print out the names
+            foreach (var p in results)
+            {
+                Console.WriteLine("Item: {0}, Cost: {1}", p.Name, p.Price);
+                if (++count == 3)
+                {
+                    break;
+                }
+            }
         }
 
     }
 
     public static class MyExtensionMethod
     {
-        public static decimal TotalPrices(this ShoppingCart cartParam)
+        public static decimal TotalPrices(this IEnumerable<Product> productEnum)
         {
             decimal total = 0;
-            foreach (Product prod in cartParam.Products)
+            foreach (Product prod in productEnum)
             {
                 total += prod.Price;
             }
             return total;
         }
+
+        public static IEnumerable<Product> FilterByCategory(this IEnumerable<Product> productEnum,
+                                                            string categoryParam)
+        {
+            foreach (Product prod in productEnum)
+            {
+                if (prod.Category == categoryParam)
+                {
+                    yield return prod;
+                }
+            }
+        }
+
+        public static IEnumerable<Product> Filter(this IEnumerable<Product> productEnum,
+            Func<Product, bool> selectorParam)
+        {
+            foreach (Product prod in productEnum)
+            {
+                if (selectorParam(prod))
+                {
+                    yield return prod;
+                }
+            }
+        }
     }
 }

chap5_essential_language_features/essential_csharp_features/ShoppingCart.cs

@@ -1,9 +1,20 @@
-using System.Collections.Generic;
+using System.Collections;
+using System.Collections.Generic;
 
 namespace automatically_implemented_properties
 {
-    public class ShoppingCart
+    public class ShoppingCart : IEnumerable<Product>
     {
         public List<Product> Products { get; set; }
+
+        public IEnumerator<Product> GetEnumerator()
+        {
+            return Products.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
     }
 }