Update the specification pattern example

Author: nemanjarogic

src/AdditionalPatterns/Specification/ProductSpecification/Domain/Entity.cs

@@ -7,9 +7,9 @@ protected Entity()
         Id = Guid.NewGuid();
     }
 
-    public Guid Id { get; protected set; }
+    public Guid Id { get; init; }
 
-    public static bool operator ==(Entity a, Entity b)
+    public static bool operator ==(Entity? a, Entity? b)
     {
         if (a is null && b is null)
         {
@@ -28,9 +28,7 @@ protected Entity()
 
     public override bool Equals(object obj)
     {
-        var other = obj as Entity;
-
-        if (other is null)
+        if (obj is not Entity other)
         {
             return false;
         }

src/AdditionalPatterns/Specification/ProductSpecification/Domain/Product.cs

@@ -2,12 +2,7 @@
 
 public class Product : Entity
 {
-    public Product(
-        string title,
-        ProductCategory category,
-        decimal price,
-        double rating,
-        DateTime launchDate)
+    public Product(string title, ProductCategory category, decimal price, double rating, DateTime launchDate)
         : base()
     {
         Title = title;
@@ -18,13 +13,9 @@ public Product(
     }
 
     public string Title { get; set; }
-
     public ProductCategory Category { get; set; }
-
     public decimal Price { get; set; }
-
     public double Rating { get; set; }
-
     public DateTime LaunchDate { get; set; }
 
     public override string ToString() =>

src/AdditionalPatterns/Specification/ProductSpecification/Domain/ProductCategory.cs

@@ -8,4 +8,4 @@ public enum ProductCategory
     Handmade,
     SportsAndOutdoors,
     ToysAndGames,
-}
+}

src/AdditionalPatterns/Specification/ProductSpecification/Executor.cs

@@ -12,25 +12,28 @@ public override void Execute()
     {
         var productRepository = new ProductRepository();
 
-        var recentlyLaunched = new RecentlyLaunchedProductSpecification();
-
         var cheap = new CheapProductSpecification();
         var topRated = new TopRatedProductSpecification();
-        var specification = cheap.And(topRated);
+        var cheapAndTopRated = cheap.And(topRated);
 
         Console.WriteLine("Searching for cheap and top rated products...");
-        var products = productRepository.Find(specification);
+        var products = productRepository.Find(cheapAndTopRated);
+
+        var recentlyLaunched = new RecentlyLaunchedProductSpecification();
+        var ordinalNumber = 1;
 
         foreach (var product in products)
         {
             Console.WriteLine(Environment.NewLine);
-            Console.WriteLine(product);
+            Console.WriteLine($"{ordinalNumber}) {product}");
 
-            // Specifications could be used in different parts of the application
+            // Specifications could be used in different parts of the application.
             if (recentlyLaunched.IsSatisfiedBy(product))
             {
-                Console.WriteLine($"Sending promotional email about recently launched product '{product.Title}'");
+                Console.WriteLine($"Sending promotional email about recently launched product '{product.Title}'...");
             }
+
+            ordinalNumber++;
         }
     }
-}
+}

src/AdditionalPatterns/Specification/ProductSpecification/Infrastructure/ProductRepository.cs

@@ -11,18 +11,19 @@ public ProductRepository()
     {
         _products = new List<Product>
         {
-            new Product("Designing Data-Intensive Applications", ProductCategory.Books, 44.50m, 4.7, new DateTime(2017, 4, 18)),
-            new Product("Kindle Paperwhite", ProductCategory.Electronics, 84.99m, 4.6, new DateTime(2018, 1, 1)),
-            new Product("USB Hub", ProductCategory.Electronics, 8.99m, 4.7, DateTime.Today.AddDays(-2)),
-            new Product("Bed Sheet Set", ProductCategory.HomeAndKitchen, 35.99m, 4.2, new DateTime(2018, 8, 18)),
-            new Product("UNO Card Game", ProductCategory.ToysAndGames, 9.99m, 4.9, new DateTime(2014, 4, 14)),
+            new("Designing Data-Intensive Applications", ProductCategory.Books, 44.50m, 4.7, new DateTime(2017, 4, 18)),
+            new("Kindle Paperwhite", ProductCategory.Electronics, 84.99m, 4.6, new DateTime(2018, 1, 1)),
+            new("USB Hub", ProductCategory.Electronics, 8.99m, 4.7, DateTime.Today.AddDays(-2)),
+            new("Bed Sheet Set", ProductCategory.HomeAndKitchen, 35.99m, 4.2, new DateTime(2018, 8, 18)),
+            new("UNO Card Game", ProductCategory.ToysAndGames, 9.99m, 4.9, new DateTime(2014, 4, 14)),
         };
     }
 
     public IReadOnlyList<Product> Find(Specification<Product> specification, int page = 0, int pageSize = 100) =>
-        _products.AsQueryable()
+        _products
+            .AsQueryable()
             .Where(specification.ToExpression())
             .Skip(page * pageSize)
             .Take(pageSize)
             .ToList();
-}
+}

src/AdditionalPatterns/Specification/ProductSpecification/Specifications/Common/AndSpecification.cs

@@ -26,4 +26,4 @@ public override Expression<Func<T, bool>> ToExpression()
 
         return finalExpression;
     }
-}
+}

src/AdditionalPatterns/Specification/ProductSpecification/Specifications/Common/OrSpecification.cs

@@ -26,4 +26,4 @@ public override Expression<Func<T, bool>> ToExpression()
 
         return finalExpression;
     }
-}
+}

src/AdditionalPatterns/Specification/ProductSpecification/Specifications/Common/Specification.cs

@@ -7,8 +7,8 @@ namespace ProductSpecification.Specifications.Common;
 /// into a single unit - specification, and reuse it in different parts of the code base.
 /// There are 3 main use cases for the specification pattern:
 /// 1) Looking up data in the database - finding records that match arbitrary specification.
-/// 2) Validating objects in the memory - checking whether object we retrieved or created fits arbitrary specification.
-/// 3) Creating a new instance that matches the criteria.
+/// 2) Validating objects in the memory - checking whether an object we retrieved or created fits arbitrary specification.
+/// 3) Creating a new instance that matches a criteria.
 /// For more details see: https://enterprisecraftsmanship.com/posts/specification-pattern-c-implementation/
 /// </summary>
 /// <typeparam name="T">Entity type.</typeparam>

src/AdditionalPatterns/Specification/ProductSpecification/Specifications/RecentlyLaunchedProductSpecification.cs

@@ -1,6 +1,6 @@
-using System.Linq.Expressions;
-using ProductSpecification.Domain;
+using ProductSpecification.Domain;
 using ProductSpecification.Specifications.Common;
+using System.Linq.Expressions;
 
 namespace ProductSpecification.Specifications;
 
@@ -9,4 +9,4 @@ public class RecentlyLaunchedProductSpecification : Specification<Product>
     public override Expression<Func<Product, bool>> ToExpression() =>
         // Products are considered as recently launched if they are launched in the last 7 days
         product => DateTime.Today.AddDays(-7) <= product.LaunchDate;
-}
+}