cs11dotnet7/vscode/Chapter10/WorkingWithEFCore/Program.Queries.cs

using Microsoft.EntityFrameworkCore; // Include extension method
using Microsoft.EntityFrameworkCore.ChangeTracking; // CollectionEntry
using Packt.Shared; // Northwind, Category, Product

partial class Program
{
  static void QueryingCategories()
  {
    using (Northwind db = new())
    {
      SectionTitle("Categories and how many products they have:");

      // a query to get all categories and their related products
      IQueryable<Category>? categories;
      // = db.Categories;
      // .Include(c => c.Products);

      db.ChangeTracker.LazyLoadingEnabled = false;

      Write("Enable eager loading? (Y/N): ");
      bool eagerLoading = (ReadKey(intercept: true).Key == ConsoleKey.Y);
      bool explicitLoading = false;
      WriteLine();

      if (eagerLoading)
      {
        categories = db.Categories?.Include(c => c.Products);
      }
      else
      {
        categories = db.Categories;
        Write("Enable explicit loading? (Y/N): ");
        explicitLoading = (ReadKey(intercept: true).Key == ConsoleKey.Y);
        WriteLine();
      }

      if (categories is null)
      {
        Fail("No categories found.");
        return;
      }

      // execute query and enumerate results
      foreach (Category c in categories)
      {
        if (explicitLoading)
        {
          Write($"Explicitly load products for {c.CategoryName}? (Y/N): ");
          ConsoleKeyInfo key = ReadKey(intercept: true);
          WriteLine();

          if (key.Key == ConsoleKey.Y)
          {
            CollectionEntry<Category, Product> products =
              db.Entry(c).Collection(c2 => c2.Products);

            if (!products.IsLoaded) products.Load();
          }
        }

        WriteLine($"{c.CategoryName} has {c.Products.Count} products.");
      }
    }
  }

  static void FilteredIncludes()
  {
    using (Northwind db = new())
    {
      SectionTitle("Products with a minimum number of units in stock.");

      string? input;
      int stock;

      do
      {
        Write("Enter a minimum for units in stock: ");
        input = ReadLine();
      } while (!int.TryParse(input, out stock));

      IQueryable<Category>? categories = db.Categories?
        .Include(c => c.Products.Where(p => p.Stock >= stock));

      if (categories is null)
      {
        Fail("No categories found.");
        return;
      }

      Info($"ToQueryString: {categories.ToQueryString()}");

      foreach (Category c in categories)
      {
        WriteLine($"{c.CategoryName} has {c.Products.Count} products with a minimum of {stock} units in stock.");
        foreach (Product p in c.Products)
        {
          WriteLine($"  {p.ProductName} has {p.Stock} units in stock.");
        }
      }
    }
  }

  static void QueryingProducts()
  {
    using (Northwind db = new())
    {
      SectionTitle("Products that cost more than a price, highest at top.");

      string? input;
      decimal price;

      do
      {
        Write("Enter a product price: ");
        input = ReadLine();
      } while (!decimal.TryParse(input, out price));

      IQueryable<Product>? products = db.Products?
        .Where(product => product.Cost > price)
        .OrderByDescending(product => product.Cost);

      if (products is null)
      {
        Fail("No products found.");
        return;
      }

      Info($"ToQueryString: {products.ToQueryString()}");

      foreach (Product p in products)
      {
        WriteLine(
          "{0}: {1} costs {2:$#,##0.00} and has {3} in stock.",
          p.ProductId, p.ProductName, p.Cost, p.Stock);
      }
    }
  }

  static void QueryingWithLike()
  {
    using (Northwind db = new())
    {
      SectionTitle("Pattern matching with LIKE.");

      Write("Enter part of a product name: ");
      string? input = ReadLine();

      if (string.IsNullOrWhiteSpace(input))
      {
        Fail("You did not enter part of a product name.");
        return;
      }

      IQueryable<Product>? products = db.Products?
        .Where(p => EF.Functions.Like(p.ProductName, $"%{input}%"));

      if (products is null)
      {
        Fail("No products found.");
        return;
      }

      foreach (Product p in products)
      {
        WriteLine("{0} has {1} units in stock. Discontinued? {2}",
          p.ProductName, p.Stock, p.Discontinued);
      }
    }
  }

  static void GetRandomProduct()
  {
    using (Northwind db = new())
    {
      SectionTitle("Get a random product.");

      int? rowCount = db.Products?.Count();

      if (rowCount == null)
      {
        Fail("Products table is empty.");
        return;
      }

      Product? p = db.Products?.FirstOrDefault(
        p => p.ProductId == (int)(EF.Functions.Random() * rowCount));

      if (p == null)
      {
        Fail("Product not found.");
        return;
      }

      WriteLine($"Random product: {p.ProductId} {p.ProductName}");
    }
  }

}