Minor improvements to EF usage.

1) Queries are untracked by default.
2) Use projection query in CartSummaryComponent.
3) Removed redundant async methods.

src/MusicStore/Components/CartSummaryComponent.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc;
@@ -17,21 +18,14 @@ namespace MusicStore.Components
 
         public async Task<IViewComponentResult> InvokeAsync()
         {
-            var cartItems = await GetCartItems();
+            var cart = ShoppingCart.GetCart(DbContext, HttpContext);
             
-            ViewBag.CartCount = cartItems.Count();
+            var cartItems = await cart.GetCartAlbumTitles();
-            ViewBag.CartSummary = string.Join("\n", cartItems.Distinct());
+
+            ViewBag.CartCount = cartItems.Count;
+            ViewBag.CartSummary = string.Join("\n", cartItems);
 
             return View();
         }
-
-        private async Task<IOrderedEnumerable<string>> GetCartItems()
-        {
-            var cart = ShoppingCart.GetCart(DbContext, HttpContext);
-
-            return (await cart.GetCartItems())
-                .Select(a => a.Album.Title)
-                .OrderBy(x => x);
-        }
     }
 }

src/MusicStore/Components/GenreMenuComponent.cs

@@ -24,9 +24,9 @@ namespace MusicStore.Components
             return View(genres);
         }
 
-        private async Task<List<Genre>> GetGenres()
+        private Task<List<Genre>> GetGenres()
         {
-            return await DbContext.Genres
+            return DbContext.Genres
                 .Include(g => g.Albums).ThenInclude(a => a.OrderDetails)
                 // TODO use nested sum https://github.com/aspnet/EntityFramework/issues/3792
                 //.OrderByDescending(

src/MusicStore/Controllers/HomeController.cs

@@ -55,12 +55,12 @@ namespace MusicStore.Controllers
             return View("~/Views/Shared/AccessDenied.cshtml");
         }
 
-        private async Task<List<Album>> GetTopSellingAlbumsAsync(MusicStoreContext dbContext, int count)
+        private Task<List<Album>> GetTopSellingAlbumsAsync(MusicStoreContext dbContext, int count)
         {
             // Group the order details by album and return
             // the albums with the highest count
 
-            return await dbContext.Albums
+            return dbContext.Albums
                 .OrderByDescending(a => a.OrderDetails.Count)
                 .Take(count)
                 .ToListAsync();

src/MusicStore/Models/MusicStoreContext.cs

@@ -10,6 +10,7 @@ namespace MusicStore.Models
         public MusicStoreContext(DbContextOptions<MusicStoreContext> options)
             : base(options)
         {
+            ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
         }
 
         public DbSet<Album> Albums { get; set; }

src/MusicStore/Models/ShoppingCart.cs

@@ -88,10 +88,22 @@ namespace MusicStore.Models
 
         public Task<List<CartItem>> GetCartItems()
         {
-            return _dbContext.CartItems.
+            return _dbContext
-                Where(cart => cart.CartId == _shoppingCartId).
+                .CartItems
-                Include(c => c.Album).
+                .Where(cart => cart.CartId == _shoppingCartId)
-                ToListAsync();
+                .Include(c => c.Album)
+                .ToListAsync();
+        }
+        
+        public Task<List<string>> GetCartAlbumTitles()
+        {
+            return _dbContext
+                .CartItems
+                .Where(cart => cart.CartId == _shoppingCartId)
+                .Select(c => c.Album.Title)
+                .Distinct()
+                .OrderBy(n => n)
+                .ToListAsync();
         }
 
         public Task<int> GetCount()
@@ -110,7 +122,8 @@ namespace MusicStore.Models
             // the current price for each of those albums in the cart
             // sum all album price totals to get the cart total
 
-            return _dbContext.CartItems
+            return _dbContext
+                .CartItems
                 .Include(c => c.Album)
                 .Where(c => c.CartId == _shoppingCartId)
                 .Select(c => c.Album.Price * c.Count)

src/MusicStore/Startup.cs

@@ -43,12 +43,12 @@ namespace MusicStore
             if (useInMemoryStore)
             {
                 services.AddDbContext<MusicStoreContext>(options =>
-                            options.UseInMemoryDatabase());
+                    options.UseInMemoryDatabase());
             }
             else
             {
                 services.AddDbContext<MusicStoreContext>(options =>
-                            options.UseSqlServer(Configuration[StoreConfig.ConnectionStringKey.Replace("__", ":")]));
+                    options.UseSqlServer(Configuration[StoreConfig.ConnectionStringKey.Replace("__", ":")]));
             }
 
             // Add Identity services to the services container