Initial commit

vs4win/Chapter11/Ch11Ex02LinqQueries/Ch11Ex02LinqQueries.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-*" />
+		<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-*" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <None Update="Northwind.db">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	</ItemGroup>
+
+</Project>

vs4win/Chapter11/Ch11Ex02LinqQueries/Customer.cs

@@ -0,0 +1,40 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Packt.Shared;
+
+public class Customer
+{
+  [StringLength(5)]
+  public string CustomerId { get; set; } = null!;
+
+  [Required]
+  [StringLength(40)]
+  public string CompanyName { get; set; } = null!;
+
+  [StringLength(30)]
+  public string? ContactName { get; set; }
+
+  [StringLength(30)]
+  public string? ContactTitle { get; set; }
+
+  [StringLength(60)]
+  public string? Address { get; set; }
+
+  [StringLength(15)]
+  public string? City { get; set; }
+
+  [StringLength(15)]
+  public string? Region { get; set; }
+
+  [StringLength(10)]
+  public string? PostalCode { get; set; }
+
+  [StringLength(15)]
+  public string? Country { get; set; }
+
+  [StringLength(24)]
+  public string? Phone { get; set; }
+
+  [StringLength(24)]
+  public string? Fax { get; set; }
+}

vs4win/Chapter11/Ch11Ex02LinqQueries/Northwind.cs

@@ -0,0 +1,16 @@
+using Microsoft.EntityFrameworkCore; // DbContext, DbSet<T>
+
+namespace Packt.Shared;
+
+public class Northwind : DbContext
+{
+  public DbSet<Customer> Customers { get; set; } = null!;
+
+  protected override void OnConfiguring(
+    DbContextOptionsBuilder optionsBuilder)
+  {
+    string path = Path.Combine(Environment.CurrentDirectory, "Northwind.db");
+    string connection = $"Filename={path}";
+    optionsBuilder.UseSqlite(connection);
+  }
+}

vs4win/Chapter11/Ch11Ex02LinqQueries/Program.cs

@@ -0,0 +1,28 @@
+using Packt.Shared; // Northwind, Customer
+
+using (Northwind db = new())
+{
+  IQueryable<string?> distinctCities =
+    db.Customers.Select(c => c.City).Distinct();
+
+  WriteLine("A list of cities that at least one customer resides in:");
+  WriteLine($"{string.Join(", ", distinctCities)}");
+  WriteLine();
+
+  Write("Enter the name of a city: ");
+  string city = ReadLine()!;
+
+  IQueryable<Customer> customersInCity = db.Customers.Where(c => c.City == city);
+
+  if (customersInCity is null)
+  {
+    WriteLine($"No customers found in {city}.");
+    return;
+  }
+
+  WriteLine($"There are {customersInCity.Count()} customers in {city}:");
+  foreach (Customer c in customersInCity)
+  {
+    WriteLine($"  {c.CompanyName}");
+  }
+}

vs4win/Chapter11/Chapter11.sln

@@ -0,0 +1,43 @@
+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.2.32210.308
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "LinqWithObjects", "LinqWithObjects\LinqWithObjects.csproj", "{0712B93E-C502-4E33-8B92-698596682A76}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "LinqWithEFCore", "LinqWithEFCore\LinqWithEFCore.csproj", "{44EB1A3F-C3E2-4072-B336-61D61FE5BC59}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "LinqInParallel", "LinqInParallel\LinqInParallel.csproj", "{5962169C-AC14-4B9D-A079-0D8D293CD65C}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Ch11Ex02LinqQueries", "Ch11Ex02LinqQueries\Ch11Ex02LinqQueries.csproj", "{F972829E-E7F1-4A1B-99EB-E582C5329BBC}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{0712B93E-C502-4E33-8B92-698596682A76}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0712B93E-C502-4E33-8B92-698596682A76}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0712B93E-C502-4E33-8B92-698596682A76}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0712B93E-C502-4E33-8B92-698596682A76}.Release|Any CPU.Build.0 = Release|Any CPU
+		{44EB1A3F-C3E2-4072-B336-61D61FE5BC59}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{44EB1A3F-C3E2-4072-B336-61D61FE5BC59}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{44EB1A3F-C3E2-4072-B336-61D61FE5BC59}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{44EB1A3F-C3E2-4072-B336-61D61FE5BC59}.Release|Any CPU.Build.0 = Release|Any CPU
+		{5962169C-AC14-4B9D-A079-0D8D293CD65C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{5962169C-AC14-4B9D-A079-0D8D293CD65C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{5962169C-AC14-4B9D-A079-0D8D293CD65C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{5962169C-AC14-4B9D-A079-0D8D293CD65C}.Release|Any CPU.Build.0 = Release|Any CPU
+		{F972829E-E7F1-4A1B-99EB-E582C5329BBC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F972829E-E7F1-4A1B-99EB-E582C5329BBC}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F972829E-E7F1-4A1B-99EB-E582C5329BBC}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F972829E-E7F1-4A1B-99EB-E582C5329BBC}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {6FFEB3ED-7D40-4114-AB17-601B64A8FCE5}
+	EndGlobalSection
+EndGlobal

vs4win/Chapter11/LinqInParallel/LinqInParallel.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+</Project>

vs4win/Chapter11/LinqInParallel/Program.cs

@@ -0,0 +1,36 @@
+using System.Diagnostics; // Stopwatch
+
+Write("Press ENTER to start. "); ReadLine();
+Stopwatch watch = Stopwatch.StartNew();
+
+int max = 45;
+IEnumerable<int> numbers = Enumerable.Range(start: 1, count: max);
+
+WriteLine($"Calculating Fibonacci sequence up to term {max}. Please wait...");
+
+// int[] fibonacciNumbers = numbers
+//   .Select(number => Fibonacci(number))
+//   .ToArray();
+
+int[] fibonacciNumbers = numbers.AsParallel()
+  .Select(number => Fibonacci(number))
+  .OrderBy(number => number)
+  .ToArray();
+
+watch.Stop();
+WriteLine("{0:#,##0} elapsed milliseconds.",
+  arg0: watch.ElapsedMilliseconds);
+
+Write("Results:");
+foreach (int number in fibonacciNumbers)
+{
+  Write($" {number:N0}");
+}
+
+static int Fibonacci(int term) =>
+  term switch
+  {
+    1 => 0,
+    2 => 1,
+    _ => Fibonacci(term - 1) + Fibonacci(term - 2)
+  };

vs4win/Chapter11/LinqWithEFCore/Category.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Packt.Shared;
+
+public class Category
+{
+  public int CategoryId { get; set; }
+
+  [Required]
+  [StringLength(15)]
+  public string CategoryName { get; set; } = null!;
+
+  public string? Description { get; set; }
+}

vs4win/Chapter11/LinqWithEFCore/LinqWithEFCore.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-*" />
+		<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-*" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <None Update="Northwind.db">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	  <None Update="settings.xml">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	</ItemGroup>
+
+</Project>

vs4win/Chapter11/LinqWithEFCore/MyLinqExtensions.cs

@@ -0,0 +1,78 @@
+namespace System.Linq; // extend Microsoft's namespace
+
+public static class MyLinqExtensions
+{
+  // this is a chainable LINQ extension method
+  public static IEnumerable<T> ProcessSequence<T>(
+    this IEnumerable<T> sequence)
+  {
+    // you could do some processing here
+    return sequence;
+  }
+
+  public static IQueryable<T> ProcessSequence<T>(
+    this IQueryable<T> sequence)
+  {
+    // you could do some processing here
+    return sequence;
+  }
+
+  // these are scalar LINQ extension methods
+  public static int? Median(
+    this IEnumerable<int?> sequence)
+  {
+    var ordered = sequence.OrderBy(item => item);
+    int middlePosition = ordered.Count() / 2;
+    return ordered.ElementAt(middlePosition);
+  }
+
+  public static int? Median<T>(
+    this IEnumerable<T> sequence, Func<T, int?> selector)
+  {
+    return sequence.Select(selector).Median();
+  }
+
+  public static decimal? Median(
+    this IEnumerable<decimal?> sequence)
+  {
+    var ordered = sequence.OrderBy(item => item);
+    int middlePosition = ordered.Count() / 2;
+    return ordered.ElementAt(middlePosition);
+  }
+
+  public static decimal? Median<T>(
+    this IEnumerable<T> sequence, Func<T, decimal?> selector)
+  {
+    return sequence.Select(selector).Median();
+  }
+
+  public static int? Mode(
+    this IEnumerable<int?> sequence)
+  {
+    var grouped = sequence.GroupBy(item => item);
+    var orderedGroups = grouped.OrderByDescending(
+      group => group.Count());
+    return orderedGroups.FirstOrDefault()?.Key;
+  }
+
+  public static int? Mode<T>(
+    this IEnumerable<T> sequence, Func<T, int?> selector)
+  {
+    return sequence.Select(selector)?.Mode();
+  }
+
+  public static decimal? Mode(
+    this IEnumerable<decimal?> sequence)
+  {
+    var grouped = sequence.GroupBy(item => item);
+    var orderedGroups = grouped.OrderByDescending(
+      group => group.Count());
+    return orderedGroups.FirstOrDefault()?.Key;
+  }
+
+  public static decimal? Mode<T>(
+    this IEnumerable<T> sequence, Func<T, decimal?> selector)
+  {
+    return sequence.Select(selector).Mode();
+  }
+}

vs4win/Chapter11/LinqWithEFCore/Northwind.cs

@@ -0,0 +1,38 @@
+using Microsoft.EntityFrameworkCore; // DbContext, DbSet<T>
+
+namespace Packt.Shared;
+
+public class Northwind : DbContext
+{
+  public DbSet<Category> Categories { get; set; } = null!;
+  public DbSet<Product> Products { get; set; } = null!;
+
+  protected override void OnConfiguring(
+    DbContextOptionsBuilder optionsBuilder)
+  {
+    string path = Path.Combine(
+      Environment.CurrentDirectory, "Northwind.db");
+
+    optionsBuilder.UseSqlite($"Filename={path}");
+
+    /*
+    string connection = "Data Source=.;" +
+        "Initial Catalog=Northwind;" +
+        "Integrated Security=true;" +
+        "MultipleActiveResultSets=true;";
+
+    optionsBuilder.UseSqlServer(connection);
+    */
+  }
+
+  protected override void OnModelCreating(
+    ModelBuilder modelBuilder)
+  {
+    if (Database.ProviderName.Contains("Sqlite"))
+    {
+      modelBuilder.Entity<Product>()
+        .Property(product => product.UnitPrice)
+        .HasConversion<double>();
+    }
+  }
+}

vs4win/Chapter11/LinqWithEFCore/Product.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Packt.Shared;
+
+public class Product
+{
+  public int ProductId { get; set; }
+
+  [Required]
+  [StringLength(40)]
+  public string ProductName { get; set; } = null!;
+
+  public int? SupplierId { get; set; }
+  public int? CategoryId { get; set; }
+
+  [StringLength(20)]
+  public string? QuantityPerUnit { get; set; }
+
+  [Column(TypeName = "money")] // required for SQL Server provider
+  public decimal? UnitPrice { get; set; }
+
+  public short? UnitsInStock { get; set; }
+  public short? UnitsOnOrder { get; set; }
+  public short? ReorderLevel { get; set; }
+  public bool Discontinued { get; set; }
+}

vs4win/Chapter11/LinqWithEFCore/Program.Functions.cs

@@ -0,0 +1,205 @@
+using Packt.Shared; // Northwind, Category, Product
+using Microsoft.EntityFrameworkCore; // DbSet<T>
+using System.Xml.Linq; // XElement, XAttribute
+
+partial class Program
+{
+  static void FilterAndSort()
+  {
+    SectionTitle("Filter and sort");
+
+    using (Northwind db = new())
+    {
+      DbSet<Product> allProducts = db.Products;
+
+      IQueryable<Product> processedProducts = allProducts.ProcessSequence();
+
+      IQueryable<Product> filteredProducts =
+        processedProducts.Where(product => product.UnitPrice < 10M);
+
+      IOrderedQueryable<Product> sortedAndFilteredProducts =
+        filteredProducts.OrderByDescending(product => product.UnitPrice);
+
+      var projectedProducts = sortedAndFilteredProducts
+        .Select(product => new // anonymous type
+        {
+          product.ProductId,
+          product.ProductName,
+          product.UnitPrice
+        });
+
+      WriteLine(projectedProducts.ToQueryString());
+
+      WriteLine("Products that cost less than $10:");
+
+      foreach (var p in projectedProducts)
+      {
+        WriteLine("{0}: {1} costs {2:$#,##0.00}",
+          p.ProductId, p.ProductName, p.UnitPrice);
+      }
+      WriteLine();
+    }
+  }
+
+  static void JoinCategoriesAndProducts()
+  {
+    SectionTitle("Join categories and products");
+
+    using (Northwind db = new())
+    {
+      // join every product to its category to return 77 matches
+      var queryJoin = db.Categories.Join(
+        inner: db.Products,
+        outerKeySelector: category => category.CategoryId,
+        innerKeySelector: product => product.CategoryId,
+        resultSelector: (c, p) =>
+          new { c.CategoryName, p.ProductName, p.ProductId })
+        .OrderBy(cp => cp.CategoryName);
+
+      foreach (var item in queryJoin)
+      {
+        WriteLine("{0}: {1} is in {2}.",
+          arg0: item.ProductId,
+          arg1: item.ProductName,
+          arg2: item.CategoryName);
+      }
+    }
+  }
+
+  static void GroupJoinCategoriesAndProducts()
+  {
+    SectionTitle("Group join categories and products");
+
+    using (Northwind db = new())
+    {
+      // group all products by their category to return 8 matches
+      var queryGroup = db.Categories.AsEnumerable().GroupJoin(
+        inner: db.Products,
+        outerKeySelector: category => category.CategoryId,
+        innerKeySelector: product => product.CategoryId,
+        resultSelector: (c, matchingProducts) => new
+        {
+          c.CategoryName,
+          Products = matchingProducts.OrderBy(p => p.ProductName)
+        });
+
+      foreach (var category in queryGroup)
+      {
+        WriteLine("{0} has {1} products.",
+          arg0: category.CategoryName,
+          arg1: category.Products.Count());
+
+        foreach (var product in category.Products)
+        {
+          WriteLine($" {product.ProductName}");
+        }
+      }
+    }
+  }
+
+  static void AggregateProducts()
+  {
+    SectionTitle("Aggregate products");
+
+    using (Northwind db = new())
+    {
+      WriteLine("{0,-25} {1,10}",
+        arg0: "Product count:",
+        arg1: db.Products.Count());
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Highest product price:",
+        arg1: db.Products.Max(p => p.UnitPrice));
+
+      WriteLine("{0,-25} {1,10:N0}",
+        arg0: "Sum of units in stock:",
+        arg1: db.Products.Sum(p => p.UnitsInStock));
+
+      WriteLine("{0,-25} {1,10:N0}",
+        arg0: "Sum of units on order:",
+        arg1: db.Products.Sum(p => p.UnitsOnOrder));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Average unit price:",
+        arg1: db.Products.Average(p => p.UnitPrice));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Value of units in stock:",
+        arg1: db.Products
+          .Sum(p => p.UnitPrice * p.UnitsInStock));
+    }
+  }
+
+  static void CustomExtensionMethods()
+  {
+    SectionTitle("Custom aggregate extension methods");
+
+    using (Northwind db = new())
+    {
+      WriteLine("{0,-25} {1,10:N0}",
+        "Mean units in stock:",
+        db.Products.Average(p => p.UnitsInStock));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        "Mean unit price:",
+        db.Products.Average(p => p.UnitPrice));
+      
+      WriteLine("{0,-25} {1,10:N0}", 
+        "Median units in stock:",
+        db.Products.Median(p => p.UnitsInStock));
+      
+      WriteLine("{0,-25} {1,10:$#,##0.00}", 
+        "Median unit price:",
+        db.Products.Median(p => p.UnitPrice));
+      
+      WriteLine("{0,-25} {1,10:N0}", 
+        "Mode units in stock:",
+        db.Products.Mode(p => p.UnitsInStock));
+      
+      WriteLine("{0,-25} {1,10:$#,##0.00}", 
+        "Mode unit price:",
+        db.Products.Mode(p => p.UnitPrice));
+    }
+  }
+
+  static void OutputProductsAsXml()
+  {
+    SectionTitle("Output products as XML");
+
+    using (Northwind db = new())
+    {
+      Product[] productsArray = db.Products.ToArray();
+
+      XElement xml = new("products",
+        from p in productsArray
+        select new XElement("product",
+          new XAttribute("id", p.ProductId),
+          new XAttribute("price", p.UnitPrice),
+         new XElement("name", p.ProductName)));
+
+      WriteLine(xml.ToString());
+    }
+  }
+
+  static void ProcessSettings()
+  {
+    string path = Path.Combine(
+      Environment.CurrentDirectory, "settings.xml");
+
+    WriteLine($"Settings file path: {path}");
+    XDocument doc = XDocument.Load(path);
+
+    var appSettings = doc.Descendants("appSettings")
+      .Descendants("add")
+      .Select(node => new
+      {
+        Key = node.Attribute("key")?.Value,
+        Value = node.Attribute("value")?.Value
+      }).ToArray();
+
+    foreach (var item in appSettings)
+    {
+      WriteLine($"{item.Key}: {item.Value}");
+    }
+  }
+}

vs4win/Chapter11/LinqWithEFCore/Program.Helpers.cs

@@ -0,0 +1,12 @@
+partial class Program
+{
+  static void SectionTitle(string title)
+  {
+    ConsoleColor previousColor = ForegroundColor;
+    ForegroundColor = ConsoleColor.DarkYellow;
+    WriteLine("*");
+    WriteLine($"* {title}");
+    WriteLine("*");
+    ForegroundColor = previousColor;
+  }
+}

vs4win/Chapter11/LinqWithEFCore/Program.cs

@@ -0,0 +1,13 @@
+// FilterAndSort();
+
+// JoinCategoriesAndProducts();
+
+// GroupJoinCategoriesAndProducts();
+
+// AggregateProducts();
+
+// CustomExtensionMethods();
+
+// OutputProductsAsXml();
+
+ProcessSettings();

vs4win/Chapter11/LinqWithEFCore/settings.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<appSettings>
+	<add key="color" value="red" />
+	<add key="size" value="large" />
+	<add key="price" value="23.99" />
+</appSettings>

vs4win/Chapter11/LinqWithObjects/LinqWithObjects.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+	  <Using Include="System.Console" Static="true" />
+	  <!--<Using Remove="System.Linq" />-->
+  </ItemGroup>
+
+</Project>

vs4win/Chapter11/LinqWithObjects/Program.Functions.cs

@@ -0,0 +1,9 @@
+partial class Program
+{
+  static bool NameLongerThanFour(string name)
+  {
+    return name.Length > 4;
+  }
+
+}
+

vs4win/Chapter11/LinqWithObjects/Program.Helpers.cs

@@ -0,0 +1,23 @@
+partial class Program
+{
+  static void SectionTitle(string title)
+  {
+    ConsoleColor previousColor = ForegroundColor;
+    ForegroundColor = ConsoleColor.DarkYellow;
+    WriteLine("*");
+    WriteLine($"* {title}");
+    WriteLine("*");
+    ForegroundColor = previousColor;
+  }
+
+  static void Output(IEnumerable<string> cohort, string description = "")
+  {
+    if (!string.IsNullOrEmpty(description))
+    {
+      WriteLine(description);
+    }
+    Write(" ");
+    WriteLine(string.Join(", ", cohort.ToArray()));
+    WriteLine();
+  }
+}

vs4win/Chapter11/LinqWithObjects/Program.cs

@@ -0,0 +1,97 @@
+// a string array is a sequence that implements IEnumerable<string>
+string[] names = new[] { "Michael", "Pam", "Jim", "Dwight",
+  "Angela", "Kevin", "Toby", "Creed" };
+
+SectionTitle("Deferred execution");
+
+// Question: Which names end with an M?
+// (written using a LINQ extension method)
+var query1 = names.Where(name => name.EndsWith("m"));
+
+// Question: Which names end with an M?
+// (written using LINQ query comprehension syntax)
+var query2 = from name in names where name.EndsWith("m") select name;
+
+// Answer returned as an array of strings containing Pam and Jim
+string[] result1 = query1.ToArray();
+
+// Answer returned as a list of strings containing Pam and Jim
+List<string> result2 = query2.ToList();
+
+// Answer returned as we enumerate over the results
+foreach (string name in query1)
+{
+  WriteLine(name); // outputs Pam
+  names[2] = "Jimmy"; // change Jim to Jimmy
+  // on the second iteration Jimmy does not end with an M
+}
+
+SectionTitle("Writing queries");
+
+// Where requires a Func<T, T> delegate instance...
+// var query = names.Where(
+//   new Func<string, bool>(NameLongerThanFour));
+
+// ...but the compiler can create it for us...
+// var query = names.Where(NameLongerThanFour);
+
+// ...or we can use a lambda expression.
+IOrderedEnumerable<string> query = names
+  .Where(name => name.Length > 4)
+  .OrderBy(name => name.Length)
+  .ThenBy(name => name);
+
+foreach (string item in query)
+{
+  WriteLine(item);
+}
+
+SectionTitle("Filtering by type");
+
+List<Exception> exceptions = new()
+{
+  new ArgumentException(),
+  new SystemException(),
+  new IndexOutOfRangeException(),
+  new InvalidOperationException(),
+  new NullReferenceException(),
+  new InvalidCastException(),
+  new OverflowException(),
+  new DivideByZeroException(),
+  new ApplicationException()
+};
+
+IEnumerable<ArithmeticException> arithmeticExceptionsQuery =
+  exceptions.OfType<ArithmeticException>();
+
+foreach (ArithmeticException exception in arithmeticExceptionsQuery)
+{
+  WriteLine(exception);
+}
+
+string[] cohort1 = new[]
+  { "Rachel", "Gareth", "Jonathan", "George" };
+
+string[] cohort2 = new[]
+  { "Jack", "Stephen", "Daniel", "Jack", "Jared" };
+
+string[] cohort3 = new[]
+  { "Declan", "Jack", "Jack", "Jasmine", "Conor" };
+
+SectionTitle("The cohorts");
+
+Output(cohort1, "Cohort 1");
+Output(cohort2, "Cohort 2");
+Output(cohort3, "Cohort 3");
+
+SectionTitle("Set operations");
+
+Output(cohort2.Distinct(), "cohort2.Distinct()");
+Output(cohort2.DistinctBy(name => name.Substring(0, 2)),
+  "cohort2.DistinctBy(name => name.Substring(0, 2)):");
+Output(cohort2.Union(cohort3), "cohort2.Union(cohort3)");
+Output(cohort2.Concat(cohort3), "cohort2.Concat(cohort3)");
+Output(cohort2.Intersect(cohort3), "cohort2.Intersect(cohort3)");
+Output(cohort2.Except(cohort3), "cohort2.Except(cohort3)");
+Output(cohort1.Zip(cohort2, (c1, c2) => $"{c1} matched with {c2}"),
+  "cohort1.Zip(cohort2)");

vscode/Chapter11/Ch11Ex02LinqQueries/Ch11Ex02LinqQueries.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-*" />
+		<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-*" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <None Update="Northwind.db">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	</ItemGroup>
+
+</Project>

vscode/Chapter11/Ch11Ex02LinqQueries/Customer.cs

@@ -0,0 +1,40 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Packt.Shared;
+
+public class Customer
+{
+  [StringLength(5)]
+  public string CustomerId { get; set; } = null!;
+
+  [Required]
+  [StringLength(40)]
+  public string CompanyName { get; set; } = null!;
+
+  [StringLength(30)]
+  public string? ContactName { get; set; }
+
+  [StringLength(30)]
+  public string? ContactTitle { get; set; }
+
+  [StringLength(60)]
+  public string? Address { get; set; }
+
+  [StringLength(15)]
+  public string? City { get; set; }
+
+  [StringLength(15)]
+  public string? Region { get; set; }
+
+  [StringLength(10)]
+  public string? PostalCode { get; set; }
+
+  [StringLength(15)]
+  public string? Country { get; set; }
+
+  [StringLength(24)]
+  public string? Phone { get; set; }
+
+  [StringLength(24)]
+  public string? Fax { get; set; }
+}

vscode/Chapter11/Ch11Ex02LinqQueries/Northwind.cs

@@ -0,0 +1,16 @@
+using Microsoft.EntityFrameworkCore; // DbContext, DbSet<T>
+
+namespace Packt.Shared;
+
+public class Northwind : DbContext
+{
+  public DbSet<Customer> Customers { get; set; } = null!;
+
+  protected override void OnConfiguring(
+    DbContextOptionsBuilder optionsBuilder)
+  {
+    string path = Path.Combine(Environment.CurrentDirectory, "Northwind.db");
+    string connection = $"Filename={path}";
+    optionsBuilder.UseSqlite(connection);
+  }
+}

vscode/Chapter11/Ch11Ex02LinqQueries/Program.cs

@@ -0,0 +1,28 @@
+using Packt.Shared; // Northwind, Customer
+
+using (Northwind db = new())
+{
+  IQueryable<string?> distinctCities =
+    db.Customers.Select(c => c.City).Distinct();
+
+  WriteLine("A list of cities that at least one customer resides in:");
+  WriteLine($"{string.Join(", ", distinctCities)}");
+  WriteLine();
+
+  Write("Enter the name of a city: ");
+  string city = ReadLine()!;
+
+  IQueryable<Customer> customersInCity = db.Customers.Where(c => c.City == city);
+
+  if (customersInCity is null)
+  {
+    WriteLine($"No customers found in {city}.");
+    return;
+  }
+
+  WriteLine($"There are {customersInCity.Count()} customers in {city}:");
+  foreach (Customer c in customersInCity)
+  {
+    WriteLine($"  {c.CompanyName}");
+  }
+}

vscode/Chapter11/Chapter11.code-workspace

@@ -0,0 +1,16 @@
+{
+	"folders": [
+		{
+			"path": "LinqWithObjects"
+		},
+		{
+			"path": "LinqWithEFCore"
+		},
+		{
+			"path": "LinqInParallel"
+		},
+		{
+			"path": "Ch11Ex02LinqQueries"
+		}
+	]
+}

vscode/Chapter11/LinqInParallel/LinqInParallel.csproj

@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+</Project>

vscode/Chapter11/LinqInParallel/Program.cs

@@ -0,0 +1,36 @@
+using System.Diagnostics; // Stopwatch
+
+Write("Press ENTER to start. "); ReadLine();
+Stopwatch watch = Stopwatch.StartNew();
+
+int max = 45;
+IEnumerable<int> numbers = Enumerable.Range(start: 1, count: max);
+
+WriteLine($"Calculating Fibonacci sequence up to term {max}. Please wait...");
+
+// int[] fibonacciNumbers = numbers
+//   .Select(number => Fibonacci(number))
+//   .ToArray();
+
+int[] fibonacciNumbers = numbers.AsParallel()
+  .Select(number => Fibonacci(number))
+  .OrderBy(number => number)
+  .ToArray();
+
+watch.Stop();
+WriteLine("{0:#,##0} elapsed milliseconds.",
+  arg0: watch.ElapsedMilliseconds);
+
+Write("Results:");
+foreach (int number in fibonacciNumbers)
+{
+  Write($" {number:N0}");
+}
+
+static int Fibonacci(int term) =>
+  term switch
+  {
+    1 => 0,
+    2 => 1,
+    _ => Fibonacci(term - 1) + Fibonacci(term - 2)
+  };

vscode/Chapter11/LinqWithEFCore/Category.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Packt.Shared;
+
+public class Category
+{
+  public int CategoryId { get; set; }
+
+  [Required]
+  [StringLength(15)]
+  public string CategoryName { get; set; } = null!;
+
+  public string? Description { get; set; }
+}

vscode/Chapter11/LinqWithEFCore/LinqWithEFCore.csproj

@@ -0,0 +1,28 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+	<ItemGroup>
+		<Using Include="System.Console" Static="true" />
+	</ItemGroup>
+
+	<ItemGroup>
+		<PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="7.0.0-*" />
+		<PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="7.0.0-*" />
+	</ItemGroup>
+
+	<ItemGroup>
+	  <None Update="Northwind.db">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	  <None Update="settings.xml">
+	    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+	  </None>
+	</ItemGroup>
+
+</Project>

vscode/Chapter11/LinqWithEFCore/MyLinqExtensions.cs

@@ -0,0 +1,78 @@
+namespace System.Linq; // extend Microsoft's namespace
+
+public static class MyLinqExtensions
+{
+  // this is a chainable LINQ extension method
+  public static IEnumerable<T> ProcessSequence<T>(
+    this IEnumerable<T> sequence)
+  {
+    // you could do some processing here
+    return sequence;
+  }
+
+  public static IQueryable<T> ProcessSequence<T>(
+    this IQueryable<T> sequence)
+  {
+    // you could do some processing here
+    return sequence;
+  }
+
+  // these are scalar LINQ extension methods
+  public static int? Median(
+    this IEnumerable<int?> sequence)
+  {
+    var ordered = sequence.OrderBy(item => item);
+    int middlePosition = ordered.Count() / 2;
+    return ordered.ElementAt(middlePosition);
+  }
+
+  public static int? Median<T>(
+    this IEnumerable<T> sequence, Func<T, int?> selector)
+  {
+    return sequence.Select(selector).Median();
+  }
+
+  public static decimal? Median(
+    this IEnumerable<decimal?> sequence)
+  {
+    var ordered = sequence.OrderBy(item => item);
+    int middlePosition = ordered.Count() / 2;
+    return ordered.ElementAt(middlePosition);
+  }
+
+  public static decimal? Median<T>(
+    this IEnumerable<T> sequence, Func<T, decimal?> selector)
+  {
+    return sequence.Select(selector).Median();
+  }
+
+  public static int? Mode(
+    this IEnumerable<int?> sequence)
+  {
+    var grouped = sequence.GroupBy(item => item);
+    var orderedGroups = grouped.OrderByDescending(
+      group => group.Count());
+    return orderedGroups.FirstOrDefault()?.Key;
+  }
+
+  public static int? Mode<T>(
+    this IEnumerable<T> sequence, Func<T, int?> selector)
+  {
+    return sequence.Select(selector)?.Mode();
+  }
+
+  public static decimal? Mode(
+    this IEnumerable<decimal?> sequence)
+  {
+    var grouped = sequence.GroupBy(item => item);
+    var orderedGroups = grouped.OrderByDescending(
+      group => group.Count());
+    return orderedGroups.FirstOrDefault()?.Key;
+  }
+
+  public static decimal? Mode<T>(
+    this IEnumerable<T> sequence, Func<T, decimal?> selector)
+  {
+    return sequence.Select(selector).Mode();
+  }
+}

vscode/Chapter11/LinqWithEFCore/Northwind.cs

@@ -0,0 +1,38 @@
+using Microsoft.EntityFrameworkCore; // DbContext, DbSet<T>
+
+namespace Packt.Shared;
+
+public class Northwind : DbContext
+{
+  public DbSet<Category> Categories { get; set; } = null!;
+  public DbSet<Product> Products { get; set; } = null!;
+
+  protected override void OnConfiguring(
+    DbContextOptionsBuilder optionsBuilder)
+  {
+    string path = Path.Combine(
+      Environment.CurrentDirectory, "Northwind.db");
+
+    optionsBuilder.UseSqlite($"Filename={path}");
+
+    /*
+    string connection = "Data Source=.;" +
+        "Initial Catalog=Northwind;" +
+        "Integrated Security=true;" +
+        "MultipleActiveResultSets=true;";
+
+    optionsBuilder.UseSqlServer(connection);
+    */
+  }
+
+  protected override void OnModelCreating(
+    ModelBuilder modelBuilder)
+  {
+    if (Database.ProviderName.Contains("Sqlite"))
+    {
+      modelBuilder.Entity<Product>()
+        .Property(product => product.UnitPrice)
+        .HasConversion<double>();
+    }
+  }
+}

vscode/Chapter11/LinqWithEFCore/Product.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace Packt.Shared;
+
+public class Product
+{
+  public int ProductId { get; set; }
+
+  [Required]
+  [StringLength(40)]
+  public string ProductName { get; set; } = null!;
+
+  public int? SupplierId { get; set; }
+  public int? CategoryId { get; set; }
+
+  [StringLength(20)]
+  public string? QuantityPerUnit { get; set; }
+
+  [Column(TypeName = "money")] // required for SQL Server provider
+  public decimal? UnitPrice { get; set; }
+
+  public short? UnitsInStock { get; set; }
+  public short? UnitsOnOrder { get; set; }
+  public short? ReorderLevel { get; set; }
+  public bool Discontinued { get; set; }
+}

vscode/Chapter11/LinqWithEFCore/Program.Functions.cs

@@ -0,0 +1,205 @@
+using Packt.Shared; // Northwind, Category, Product
+using Microsoft.EntityFrameworkCore; // DbSet<T>
+using System.Xml.Linq; // XElement, XAttribute
+
+partial class Program
+{
+  static void FilterAndSort()
+  {
+    SectionTitle("Filter and sort");
+
+    using (Northwind db = new())
+    {
+      DbSet<Product> allProducts = db.Products;
+
+      IQueryable<Product> processedProducts = allProducts.ProcessSequence();
+
+      IQueryable<Product> filteredProducts =
+        processedProducts.Where(product => product.UnitPrice < 10M);
+
+      IOrderedQueryable<Product> sortedAndFilteredProducts =
+        filteredProducts.OrderByDescending(product => product.UnitPrice);
+
+      var projectedProducts = sortedAndFilteredProducts
+        .Select(product => new // anonymous type
+        {
+          product.ProductId,
+          product.ProductName,
+          product.UnitPrice
+        });
+
+      WriteLine(projectedProducts.ToQueryString());
+
+      WriteLine("Products that cost less than $10:");
+
+      foreach (var p in projectedProducts)
+      {
+        WriteLine("{0}: {1} costs {2:$#,##0.00}",
+          p.ProductId, p.ProductName, p.UnitPrice);
+      }
+      WriteLine();
+    }
+  }
+
+  static void JoinCategoriesAndProducts()
+  {
+    SectionTitle("Join categories and products");
+
+    using (Northwind db = new())
+    {
+      // join every product to its category to return 77 matches
+      var queryJoin = db.Categories.Join(
+        inner: db.Products,
+        outerKeySelector: category => category.CategoryId,
+        innerKeySelector: product => product.CategoryId,
+        resultSelector: (c, p) =>
+          new { c.CategoryName, p.ProductName, p.ProductId })
+        .OrderBy(cp => cp.CategoryName);
+
+      foreach (var item in queryJoin)
+      {
+        WriteLine("{0}: {1} is in {2}.",
+          arg0: item.ProductId,
+          arg1: item.ProductName,
+          arg2: item.CategoryName);
+      }
+    }
+  }
+
+  static void GroupJoinCategoriesAndProducts()
+  {
+    SectionTitle("Group join categories and products");
+
+    using (Northwind db = new())
+    {
+      // group all products by their category to return 8 matches
+      var queryGroup = db.Categories.AsEnumerable().GroupJoin(
+        inner: db.Products,
+        outerKeySelector: category => category.CategoryId,
+        innerKeySelector: product => product.CategoryId,
+        resultSelector: (c, matchingProducts) => new
+        {
+          c.CategoryName,
+          Products = matchingProducts.OrderBy(p => p.ProductName)
+        });
+
+      foreach (var category in queryGroup)
+      {
+        WriteLine("{0} has {1} products.",
+          arg0: category.CategoryName,
+          arg1: category.Products.Count());
+
+        foreach (var product in category.Products)
+        {
+          WriteLine($" {product.ProductName}");
+        }
+      }
+    }
+  }
+
+  static void AggregateProducts()
+  {
+    SectionTitle("Aggregate products");
+
+    using (Northwind db = new())
+    {
+      WriteLine("{0,-25} {1,10}",
+        arg0: "Product count:",
+        arg1: db.Products.Count());
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Highest product price:",
+        arg1: db.Products.Max(p => p.UnitPrice));
+
+      WriteLine("{0,-25} {1,10:N0}",
+        arg0: "Sum of units in stock:",
+        arg1: db.Products.Sum(p => p.UnitsInStock));
+
+      WriteLine("{0,-25} {1,10:N0}",
+        arg0: "Sum of units on order:",
+        arg1: db.Products.Sum(p => p.UnitsOnOrder));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Average unit price:",
+        arg1: db.Products.Average(p => p.UnitPrice));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        arg0: "Value of units in stock:",
+        arg1: db.Products
+          .Sum(p => p.UnitPrice * p.UnitsInStock));
+    }
+  }
+
+  static void CustomExtensionMethods()
+  {
+    SectionTitle("Custom aggregate extension methods");
+
+    using (Northwind db = new())
+    {
+      WriteLine("{0,-25} {1,10:N0}",
+        "Mean units in stock:",
+        db.Products.Average(p => p.UnitsInStock));
+
+      WriteLine("{0,-25} {1,10:$#,##0.00}",
+        "Mean unit price:",
+        db.Products.Average(p => p.UnitPrice));
+      
+      WriteLine("{0,-25} {1,10:N0}", 
+        "Median units in stock:",
+        db.Products.Median(p => p.UnitsInStock));
+      
+      WriteLine("{0,-25} {1,10:$#,##0.00}", 
+        "Median unit price:",
+        db.Products.Median(p => p.UnitPrice));
+      
+      WriteLine("{0,-25} {1,10:N0}", 
+        "Mode units in stock:",
+        db.Products.Mode(p => p.UnitsInStock));
+      
+      WriteLine("{0,-25} {1,10:$#,##0.00}", 
+        "Mode unit price:",
+        db.Products.Mode(p => p.UnitPrice));
+    }
+  }
+
+  static void OutputProductsAsXml()
+  {
+    SectionTitle("Output products as XML");
+
+    using (Northwind db = new())
+    {
+      Product[] productsArray = db.Products.ToArray();
+
+      XElement xml = new("products",
+        from p in productsArray
+        select new XElement("product",
+          new XAttribute("id", p.ProductId),
+          new XAttribute("price", p.UnitPrice),
+         new XElement("name", p.ProductName)));
+
+      WriteLine(xml.ToString());
+    }
+  }
+
+  static void ProcessSettings()
+  {
+    string path = Path.Combine(
+      Environment.CurrentDirectory, "settings.xml");
+
+    WriteLine($"Settings file path: {path}");
+    XDocument doc = XDocument.Load(path);
+
+    var appSettings = doc.Descendants("appSettings")
+      .Descendants("add")
+      .Select(node => new
+      {
+        Key = node.Attribute("key")?.Value,
+        Value = node.Attribute("value")?.Value
+      }).ToArray();
+
+    foreach (var item in appSettings)
+    {
+      WriteLine($"{item.Key}: {item.Value}");
+    }
+  }
+}

vscode/Chapter11/LinqWithEFCore/Program.Helpers.cs

@@ -0,0 +1,12 @@
+partial class Program
+{
+  static void SectionTitle(string title)
+  {
+    ConsoleColor previousColor = ForegroundColor;
+    ForegroundColor = ConsoleColor.DarkYellow;
+    WriteLine("*");
+    WriteLine($"* {title}");
+    WriteLine("*");
+    ForegroundColor = previousColor;
+  }
+}

vscode/Chapter11/LinqWithEFCore/Program.cs

@@ -0,0 +1,13 @@
+// FilterAndSort();
+
+// JoinCategoriesAndProducts();
+
+// GroupJoinCategoriesAndProducts();
+
+// AggregateProducts();
+
+// CustomExtensionMethods();
+
+// OutputProductsAsXml();
+
+ProcessSettings();

vscode/Chapter11/LinqWithEFCore/settings.xml

@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<appSettings>
+	<add key="color" value="red" />
+	<add key="size" value="large" />
+	<add key="price" value="23.99" />
+</appSettings>

vscode/Chapter11/LinqWithObjects/LinqWithObjects.csproj

@@ -0,0 +1,15 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+	  <Using Include="System.Console" Static="true" />
+	  <!--<Using Remove="System.Linq" />-->
+  </ItemGroup>
+
+</Project>

vscode/Chapter11/LinqWithObjects/Program.Functions.cs

@@ -0,0 +1,9 @@
+partial class Program
+{
+  static bool NameLongerThanFour(string name)
+  {
+    return name.Length > 4;
+  }
+
+}
+

vscode/Chapter11/LinqWithObjects/Program.Helpers.cs

@@ -0,0 +1,23 @@
+partial class Program
+{
+  static void SectionTitle(string title)
+  {
+    ConsoleColor previousColor = ForegroundColor;
+    ForegroundColor = ConsoleColor.DarkYellow;
+    WriteLine("*");
+    WriteLine($"* {title}");
+    WriteLine("*");
+    ForegroundColor = previousColor;
+  }
+
+  static void Output(IEnumerable<string> cohort, string description = "")
+  {
+    if (!string.IsNullOrEmpty(description))
+    {
+      WriteLine(description);
+    }
+    Write(" ");
+    WriteLine(string.Join(", ", cohort.ToArray()));
+    WriteLine();
+  }
+}

vscode/Chapter11/LinqWithObjects/Program.cs

@@ -0,0 +1,97 @@
+// a string array is a sequence that implements IEnumerable<string>
+string[] names = new[] { "Michael", "Pam", "Jim", "Dwight",
+  "Angela", "Kevin", "Toby", "Creed" };
+
+SectionTitle("Deferred execution");
+
+// Question: Which names end with an M?
+// (written using a LINQ extension method)
+var query1 = names.Where(name => name.EndsWith("m"));
+
+// Question: Which names end with an M?
+// (written using LINQ query comprehension syntax)
+var query2 = from name in names where name.EndsWith("m") select name;
+
+// Answer returned as an array of strings containing Pam and Jim
+string[] result1 = query1.ToArray();
+
+// Answer returned as a list of strings containing Pam and Jim
+List<string> result2 = query2.ToList();
+
+// Answer returned as we enumerate over the results
+foreach (string name in query1)
+{
+  WriteLine(name); // outputs Pam
+  names[2] = "Jimmy"; // change Jim to Jimmy
+  // on the second iteration Jimmy does not end with an M
+}
+
+SectionTitle("Writing queries");
+
+// Where requires a Func<T, T> delegate instance...
+// var query = names.Where(
+//   new Func<string, bool>(NameLongerThanFour));
+
+// ...but the compiler can create it for us...
+// var query = names.Where(NameLongerThanFour);
+
+// ...or we can use a lambda expression.
+IOrderedEnumerable<string> query = names
+  .Where(name => name.Length > 4)
+  .OrderBy(name => name.Length)
+  .ThenBy(name => name);
+
+foreach (string item in query)
+{
+  WriteLine(item);
+}
+
+SectionTitle("Filtering by type");
+
+List<Exception> exceptions = new()
+{
+  new ArgumentException(),
+  new SystemException(),
+  new IndexOutOfRangeException(),
+  new InvalidOperationException(),
+  new NullReferenceException(),
+  new InvalidCastException(),
+  new OverflowException(),
+  new DivideByZeroException(),
+  new ApplicationException()
+};
+
+IEnumerable<ArithmeticException> arithmeticExceptionsQuery =
+  exceptions.OfType<ArithmeticException>();
+
+foreach (ArithmeticException exception in arithmeticExceptionsQuery)
+{
+  WriteLine(exception);
+}
+
+string[] cohort1 = new[]
+  { "Rachel", "Gareth", "Jonathan", "George" };
+
+string[] cohort2 = new[]
+  { "Jack", "Stephen", "Daniel", "Jack", "Jared" };
+
+string[] cohort3 = new[]
+  { "Declan", "Jack", "Jack", "Jasmine", "Conor" };
+
+SectionTitle("The cohorts");
+
+Output(cohort1, "Cohort 1");
+Output(cohort2, "Cohort 2");
+Output(cohort3, "Cohort 3");
+
+SectionTitle("Set operations");
+
+Output(cohort2.Distinct(), "cohort2.Distinct()");
+Output(cohort2.DistinctBy(name => name.Substring(0, 2)),
+  "cohort2.DistinctBy(name => name.Substring(0, 2)):");
+Output(cohort2.Union(cohort3), "cohort2.Union(cohort3)");
+Output(cohort2.Concat(cohort3), "cohort2.Concat(cohort3)");
+Output(cohort2.Intersect(cohort3), "cohort2.Intersect(cohort3)");
+Output(cohort2.Except(cohort3), "cohort2.Except(cohort3)");
+Output(cohort1.Zip(cohort2, (c1, c2) => $"{c1} matched with {c2}"),
+  "cohort1.Zip(cohort2)");