Initial commit

vscode/Chapter11/LinqWithEFCore/Program.Functions.cs

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+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}");
+    }
+  }
+}