cs11dotnet7/vscode/Chapter11/LinqWithEFCore/Program.Functions.cs

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())
    {
      // Try to get an efficient count from EF Core DbSet<T>.
      if (db.Products.TryGetNonEnumeratedCount(out int countDbSet))
      {
        WriteLine("{0,-25} {1,10}",
          arg0: "Product count from DbSet:",
          arg1: countDbSet);
      }
      else
      {
        WriteLine("Products DbSet does not have a Count property.");
      }

      // Try to get an efficient count from a List<T>.
      List<Product> products = db.Products.ToList();

      if (products.TryGetNonEnumeratedCount(out int countList))
      {
        WriteLine("{0,-25} {1,10}",
          arg0: "Product count from list:",
          arg1: countList);
      }
      else
      {
        WriteLine("Products list does not have a Count property.");
      }

      WriteLine("{0,-25} {1,10}",
        arg0: "Product count:",
        arg1: db.Products.Count());

      WriteLine("{0,-27} {1,8}", // Note the different column widths.
        arg0: "Discontinued product count:",
        arg1: db.Products.Count(product => product.Discontinued));

      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 OutputTableOfProducts(Product[] products, 
    int currentPage, int totalPages)
  {
    string line = new('-', count: 73);
    string lineHalf = new('-', count: 30);

    WriteLine(line);
    WriteLine("{0,4} {1,-40} {2,12} {3,-15}",
      "ID", "Product Name", "Unit Price", "Discontinued");
    WriteLine(line);

    foreach (Product p in products)
    {
      WriteLine("{0,4} {1,-40} {2,12:C} {3,-15}",
        p.ProductId, p.ProductName, p.UnitPrice, p.Discontinued);
    }
    WriteLine("{0} Page {1} of {2} {3}",
      lineHalf, currentPage + 1, totalPages + 1, lineHalf);
  }

  static void OutputPageOfProducts(IQueryable<Product> products,
    int pageSize, int currentPage, int totalPages)
  {
    // We must order data before skipping and taking to ensure
    // the data is not randomly sorted in each page.
    var pagingQuery = products.OrderBy(p => p.ProductId)
      .Skip(currentPage * pageSize).Take(pageSize);

    // SectionTitle(pagingQuery.ToQueryString());

    OutputTableOfProducts(pagingQuery.ToArray(), 
      currentPage, totalPages);
  }

  static void PagingProducts()
  {
    SectionTitle("Paging products");

    using (Northwind db = new())
    {
      int pageSize = 10;
      int currentPage = 0;
      int productCount = db.Products.Count();
      int totalPages = productCount / pageSize;

      while (true)
      {
        OutputPageOfProducts(db.Products, pageSize, currentPage, totalPages);

        Write("Press <- to page back, press -> to page forward, any key to exit.");
        ConsoleKey key = ReadKey().Key;

        if (key == ConsoleKey.LeftArrow)
          if (currentPage == 0)
            currentPage = totalPages;
          else
            currentPage--;
        else if (key == ConsoleKey.RightArrow)
          if (currentPage == totalPages)
            currentPage = 0;
          else
            currentPage++;
        else
          break; // out of the while loop.

        WriteLine();
      }
    }
  }

  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}");
    }
  }
}