Add async LoadFromQueryable

It is primarily based on the IAsyncEnumerable interface,
but requires some hacks to get access to the CountAsync method.

src/Framework/Core/Controls/GridViewDataSetExtensions.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace DotVVM.Framework.Controls
@@ -35,6 +37,44 @@ public static void LoadFromQueryable<T>(this IGridViewDataSet<T> dataSet, IQuery
             dataSet.IsRefreshRequired = false;
         }
 
+        public static async Task LoadFromQueryableAsync<T>(this IGridViewDataSet<T> dataSet, IQueryable<T> queryable, CancellationToken cancellationToken = default)
+        {
+            if (dataSet.FilteringOptions is not IApplyToQueryable filteringOptions)
+            {
+                throw new ArgumentException($"The FilteringOptions of {dataSet.GetType()} must implement IApplyToQueryable!");
+            }
+            if (dataSet.SortingOptions is not IApplyToQueryable sortingOptions)
+            {
+                throw new ArgumentException($"The SortingOptions of {dataSet.GetType()} must implement IApplyToQueryable!");
+            }
+            if (dataSet.PagingOptions is not IApplyToQueryable pagingOptions)
+            {
+                throw new ArgumentException($"The PagingOptions of {dataSet.GetType()} must implement IApplyToQueryable!");
+            }
+
+            var filtered = filteringOptions.ApplyToQueryable(queryable);
+            var sorted = sortingOptions.ApplyToQueryable(filtered);
+            var paged = pagingOptions.ApplyToQueryable(sorted);
+            if (paged is not IAsyncEnumerable<T> asyncPaged)
+            {
+                throw new ArgumentException($"The specified IQueryable ({queryable.GetType().FullName}), does not support async enumeration. Please use the LoadFromQueryable method.", nameof(queryable));
+            }
+
+            var result = new List<T>();
+            await foreach (var item in asyncPaged.WithCancellation(cancellationToken))
+            {
+                result.Add(item);
+            }
+            dataSet.Items = result;
+
+            if (pagingOptions is IPagingOptionsLoadingPostProcessor pagingOptionsLoadingPostProcessor)
+            {
+                await pagingOptionsLoadingPostProcessor.ProcessLoadedItemsAsync(filtered, result, cancellationToken);
+            }
+
+            dataSet.IsRefreshRequired = false;
+        }
+
         public static void GoToFirstPageAndRefresh(this IPageableGridViewDataSet<IPagingFirstPageCapability> dataSet)
         {
             dataSet.PagingOptions.GoToFirstPage();

src/Framework/Core/Controls/Options/IPagingOptionsLoadingPostProcessor.cs

@@ -1,10 +1,13 @@
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace DotVVM.Framework.Controls;
 
 /// <summary> Provides an extension point to the <see cref="GridViewDataSetExtensions.LoadFromQueryable{T}(DotVVM.Framework.Controls.IGridViewDataSet{T}, IQueryable{T})" /> method, which is invoked after the items are loaded from database. </summary>
 public interface IPagingOptionsLoadingPostProcessor
 {
     void ProcessLoadedItems<T>(IQueryable<T> filteredQueryable, IList<T> items);
+    Task ProcessLoadedItemsAsync<T>(IQueryable<T> filteredQueryable, IList<T> items, CancellationToken cancellationToken);
 }

src/Framework/Core/Controls/Options/PagingImplementation.cs

@@ -1,9 +1,15 @@
-using System.Linq;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace DotVVM.Framework.Controls
 {
     public static class PagingImplementation
     {
+        public static Func<IQueryable, CancellationToken, Task<int?>>? CustomAsyncQueryableCountDelegate;
 
         /// <summary>
         /// Applies paging to the <paramref name="queryable" /> after the total number
@@ -17,6 +23,87 @@ public static IQueryable<T> ApplyPagingToQueryable<T, TPagingOptions>(IQueryable
                 ? queryable.Skip(options.PageSize * options.PageIndex).Take(options.PageSize)
                 : queryable;
         }
-    }
 
+        /// <summary> Attempts to count the queryable asynchronously. EF Core IQueryables are supported, and IQueryables which return IAsyncEnumerable from GroupBy operator also work correctly. Otherwise, a synchronous fallback is user, or <see cref="CustomAsyncQueryableCountDelegate" /> may be set to add support for an ORM mapper of choice. </summary>
+        public static async Task<int> QueryableAsyncCount<T>(IQueryable<T> queryable, CancellationToken ct = default)
+        {
+            if (CustomAsyncQueryableCountDelegate is {} customDelegate)
+            {
+                var result = await customDelegate(queryable, ct);
+                if (result.HasValue)
+                {
+                    return result.Value;
+                }
+            }
+
+            var queryableType = queryable.GetType();
+            return await (
+                EfCoreAsyncCountHack(queryable, queryableType, ct) ?? // TODO: test this
+                Ef6AsyncCountHack(queryable, ct) ?? // TODO: test this
+                StandardAsyncCountHack(queryable, ct)
+            );
+        }
+
+        static MethodInfo? efMethodCache;
+        static Task<int>? EfCoreAsyncCountHack<T>(IQueryable<T> queryable, Type queryableType, CancellationToken ct)
+        {
+            if (!(
+                queryableType.Namespace == "Microsoft.EntityFrameworkCore.Query.Internal" && queryableType.Name == "EntityQueryable`1" ||
+                queryableType.Namespace == "Microsoft.EntityFrameworkCore.Internal" && queryableType.Name == "InternalDbSet`1"
+            ))
+                return null;
+
+            var countMethod = efMethodCache ?? queryableType.Assembly.GetType("Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions")!.GetMethods().SingleOrDefault(m => m.Name == "CountAsync" && m.GetParameters() is { Length: 2 } parameters && parameters[1].ParameterType == typeof(CancellationToken));
+            if (countMethod is null)
+                return null;
+
+            if (efMethodCache is null)
+                Interlocked.CompareExchange(ref efMethodCache, countMethod, null);
+
+            var countMethodGeneric = countMethod.MakeGenericMethod(typeof(T));
+            return (Task<int>)countMethodGeneric.Invoke(null, new object[] { queryable, ct })!;
+        }
+
+        static readonly Type? ef6IDbAsyncQueryProvider = Type.GetType("System.Data.Entity.Infrastructure.IDbAsyncQueryProvider, EntityFramework"); // https://learn.microsoft.com/en-us/dotnet/api/system.data.entity.infrastructure.idbasyncqueryprovider?view=entity-framework-6.2.0
+        static MethodInfo? ef6MethodCache;
+        static Task<int>? Ef6AsyncCountHack<T>(IQueryable<T> queryable, CancellationToken ct)
+        {
+            if (ef6IDbAsyncQueryProvider is null)
+                return null;
+            if (!ef6IDbAsyncQueryProvider.IsInstanceOfType(queryable.Provider))
+                return null;
+
+            var countMethod = ef6MethodCache ?? Type.GetType("System.Data.Entity.QueryableExtensions, EntityFramework")!.GetMethods().SingleOrDefault(m => m.Name == "CountAsync" && m.GetParameters() is { Length: 2 } parameters && parameters[1].ParameterType == typeof(CancellationToken))!;
+            if (countMethod is null)
+                return null;
+
+            if (ef6MethodCache is null)
+                Interlocked.CompareExchange(ref ef6MethodCache, countMethod, null);
+
+            var countMethodGeneric = countMethod.MakeGenericMethod(typeof(T));
+            return (Task<int>)countMethodGeneric.Invoke(null, new object[] { queryable, ct })!;
+        }
+
+        static Task<int> StandardAsyncCountHack<T>(IQueryable<T> queryable, CancellationToken ct)
+        {
+#if NETSTANDARD2_1_OR_GREATER
+            var countGroupHack = queryable.GroupBy(_ => 1).Select(group => group.Count());
+            // if not IAsyncEnumerable, just use synchronous Count
+            if (countGroupHack is not IAsyncEnumerable<int> countGroupEnumerable)
+            {
+                return Task.FromResult(queryable.Count());
+            }
+
+            return FirstOrDefaultAsync(countGroupEnumerable, ct);
+        }
+
+        static async Task<T?> FirstOrDefaultAsync<T>(IAsyncEnumerable<T> enumerable, CancellationToken ct)
+        {
+            await using var enumerator = enumerable.GetAsyncEnumerator(ct);
+            return await enumerator.MoveNextAsync() ? enumerator.Current : default;
+#else
+            throw new Exception("IAsyncEnumerable is not supported on .NET Framework and the queryable does not support EntityFramework CountAsync.");
+#endif
+        }
+    }
 }

src/Framework/Core/Controls/Options/PagingOptions.cs

@@ -1,6 +1,8 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
 using DotVVM.Framework.ViewModel;
 
 namespace DotVVM.Framework.Controls
@@ -125,5 +127,10 @@ public virtual void ProcessLoadedItems<T>(IQueryable<T> filteredQueryable, IList
         {
             TotalItemsCount = filteredQueryable.Count();
         }
+        public async Task ProcessLoadedItemsAsync<T>(IQueryable<T> filteredQueryable, IList<T> items, CancellationToken cancellationToken)
+        {
+            TotalItemsCount = await PagingImplementation.QueryableAsyncCount(filteredQueryable, cancellationToken);
+        }
+
     }
 }

src/Samples/Common/ViewModels/ControlSamples/GridView/GridViewStaticCommandViewModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using DotVVM.Framework.Controls;
 using DotVVM.Framework.ViewModel;
@@ -123,6 +124,12 @@ public void ProcessLoadedItems<T>(IQueryable<T> filteredQueryable, IList<T> item
                     NextPageToken = lastToken.ToString();
                 }
             }
+
+            Task IPagingOptionsLoadingPostProcessor.ProcessLoadedItemsAsync<T>(IQueryable<T> filteredQueryable, IList<T> items, CancellationToken cancellationToken)
+            {
+                ProcessLoadedItems(filteredQueryable, items);
+                return Task.CompletedTask;
+            }
         }
 
         public class NextTokenHistoryGridViewDataSet() : GenericGridViewDataSet<CustomerData, NoFilteringOptions, SortingOptions, CustomerDataNextTokenHistoryPagingOptions, RowInsertOptions<CustomerData>, RowEditOptions>(
@@ -165,6 +172,12 @@ public void ProcessLoadedItems<T>(IQueryable<T> filteredQueryable, IList<T> item
                     TokenHistory.Add((lastToken ?? 0).ToString());
                 }
             }
+
+            Task IPagingOptionsLoadingPostProcessor.ProcessLoadedItemsAsync<T>(IQueryable<T> filteredQueryable, IList<T> items, CancellationToken cancellationToken)
+            {
+                ProcessLoadedItems(filteredQueryable, items);
+                return Task.CompletedTask;
+            }
         }
 
         public class MultiSortGridViewDataSet() : GenericGridViewDataSet<CustomerData, NoFilteringOptions, MultiCriteriaSortingOptions, PagingOptions, RowInsertOptions<CustomerData>, RowEditOptions>(

src/Tests/DotVVM.Framework.Tests.csproj

@@ -42,6 +42,8 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">
     <ProjectReference Include="../Framework/Hosting.AspNetCore/DotVVM.Framework.Hosting.AspNetCore.csproj" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="8.0.8" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="8.0.8" />
     <PackageReference Include="CheckTestOutput" Version="0.6.3" />
   </ItemGroup>
   <ItemGroup>

src/Tests/ViewModel/EFCoreGridViewDataSetTests.cs

@@ -0,0 +1,139 @@
+#if NET8_0_OR_GREATER
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using DotVVM.Framework.Controls;
+using DotVVM.Framework.ViewModel;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace DotVVM.Framework.Tests.ViewModel
+{
+    [TestClass]
+    public class EFCoreGridViewDataSetTests
+    {
+        private readonly DbContextOptions<MyDbContext> contextOptions;
+
+        public EFCoreGridViewDataSetTests()
+        {
+            contextOptions = new DbContextOptionsBuilder<MyDbContext>()
+                .UseInMemoryDatabase("BloggingControllerTest")
+                .ConfigureWarnings(b => b.Ignore(InMemoryEventId.TransactionIgnoredWarning))
+                .Options;
+        }
+
+        class MyDbContext: DbContext
+        {
+            public MyDbContext(DbContextOptions options) : base(options)
+            {
+            }
+
+            public DbSet<Entry> Entries { get; set; }
+        }
+
+        record Entry(int Id, string Name, int SomethingElse = 0);
+
+        MyDbContext Init()
+        {
+            var context = new MyDbContext(contextOptions);
+            context.Database.EnsureDeleted();
+            context.Database.EnsureCreated();
+            context.Entries.AddRange([
+                new (1, "Z"),
+                new (2, "Y"),
+                new (3, "X"),
+                new (4, "W"),
+                new (5, "V"),
+                new (6, "U", 5),
+                new (7, "T", 5),
+                new (8, "S", 5),
+                new (9, "R", 3),
+                new (10, "Q", 3),
+            ]);
+            context.SaveChanges();
+            return context;
+        }
+
+        [TestMethod]
+        public void LoadData_PagingSorting()
+        {
+            using var context = Init();
+
+            var dataSet = new GridViewDataSet<Entry>()
+            {
+                PagingOptions = { PageSize = 3, PageIndex = 0 },
+                SortingOptions = { SortExpression = nameof(Entry.Name), SortDescending = false },
+            };
+
+            dataSet.LoadFromQueryable(context.Entries);
+
+            Assert.AreEqual(3, dataSet.Items.Count);
+            Assert.AreEqual(10, dataSet.PagingOptions.TotalItemsCount);
+            Assert.AreEqual(10, dataSet.Items[0].Id);
+            Assert.AreEqual(9, dataSet.Items[1].Id);
+            Assert.AreEqual(8, dataSet.Items[2].Id);
+        }
+
+        [TestMethod]
+        public void LoadData_PagingSorting_PreFiltered()
+        {
+            using var context = Init();
+
+            var dataSet = new GridViewDataSet<Entry>()
+            {
+                PagingOptions = { PageSize = 3, PageIndex = 0 },
+                SortingOptions = { SortExpression = nameof(Entry.Name), SortDescending = false },
+            };
+
+            dataSet.LoadFromQueryable(context.Entries.Where(e => e.SomethingElse == 3));
+
+            Assert.AreEqual(2, dataSet.Items.Count);
+            Assert.AreEqual(2, dataSet.PagingOptions.TotalItemsCount);
+            Assert.AreEqual(10, dataSet.Items[0].Id);
+            Assert.AreEqual(9, dataSet.Items[1].Id);
+        }
+
+        [TestMethod]
+        public async Task LoadData_PagingSortingAsync()
+        {
+            using var context = Init();
+
+            var dataSet = new GridViewDataSet<Entry>()
+            {
+                PagingOptions = { PageSize = 3, PageIndex = 0 },
+                SortingOptions = { SortExpression = nameof(Entry.Name), SortDescending = false },
+            };
+
+            await dataSet.LoadFromQueryableAsync(context.Entries);
+
+            Assert.AreEqual(3, dataSet.Items.Count);
+            Assert.AreEqual(10, dataSet.PagingOptions.TotalItemsCount);
+            Assert.AreEqual(10, dataSet.Items[0].Id);
+            Assert.AreEqual(9, dataSet.Items[1].Id);
+            Assert.AreEqual(8, dataSet.Items[2].Id);
+        }
+
+        [TestMethod]
+        public async Task LoadData_PagingSorting_PreFilteredAsync()
+        {
+            using var context = Init();
+
+            var dataSet = new GridViewDataSet<Entry>()
+            {
+                PagingOptions = { PageSize = 3, PageIndex = 0 },
+                SortingOptions = { SortExpression = nameof(Entry.Name), SortDescending = false },
+            };
+
+            await dataSet.LoadFromQueryableAsync(context.Entries.Where(e => e.SomethingElse == 3));
+
+            Assert.AreEqual(2, dataSet.Items.Count);
+            Assert.AreEqual(2, dataSet.PagingOptions.TotalItemsCount);
+            Assert.AreEqual(10, dataSet.Items[0].Id);
+            Assert.AreEqual(9, dataSet.Items[1].Id);
+        }
+    }
+}
+#endif