Re-adding BasketQueryService

src/Infrastructure/Data/Queries/BasketQueryService.cs

@@ -0,0 +1,31 @@
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.eShopWeb.ApplicationCore.Interfaces;
+
+namespace Microsoft.eShopWeb.Infrastructure.Data.Queries;
+
+public class BasketQueryService : IBasketQueryService
+{
+    private readonly CatalogContext _dbContext;
+
+    public BasketQueryService(CatalogContext dbContext)
+    {
+        _dbContext = dbContext;
+    }
+
+    /// <summary>
+    /// This method performs the sum on the database rather than in memory
+    /// </summary>
+    /// <param name="username"></param>
+    /// <returns></returns>
+    public async Task<int> CountTotalBasketItems(string username)
+    {
+        var totalItems = await _dbContext.Baskets
+            .Where(basket => basket.BuyerId == username)
+            .SelectMany(item => item.Items)
+            .SumAsync(sum => sum.Quantity);
+
+        return totalItems;
+    }
+}