Query : Add support for final GroupBy operator

src/EFCore.InMemory/Extensions/InMemoryServiceCollectionExtensions.cs

@@ -48,6 +48,7 @@ public static IServiceCollection AddEntityFrameworkInMemoryDatabase(this IServic
             .TryAdd<ITypeMappingSource, InMemoryTypeMappingSource>()
             .TryAdd<IShapedQueryCompilingExpressionVisitorFactory, InMemoryShapedQueryCompilingExpressionVisitorFactory>()
             .TryAdd<IQueryableMethodTranslatingExpressionVisitorFactory, InMemoryQueryableMethodTranslatingExpressionVisitorFactory>()
+            .TryAdd<IQueryTranslationPreprocessorFactory, InMemoryQueryTranslationPreprocessorFactory>()
             .TryAdd<ISingletonOptions, IInMemorySingletonOptions>(p => p.GetRequiredService<IInMemorySingletonOptions>())
             .TryAddProviderSpecificServices(
                 b => b

src/EFCore.InMemory/Properties/InMemoryStrings.resx

@@ -134,6 +134,9 @@
     <value>Transactions are not supported by the in-memory store. See http://go.microsoft.com/fwlink/?LinkId=800142</value>
     <comment>Warning InMemoryEventId.TransactionIgnoredWarning</comment>
   </data>
+  <data name="NonComposedGroupByNotSupported" xml:space="preserve">
+    <value>A 'GroupBy' operation which is not composed into aggregate or projection of elements is not supported.</value>
+  </data>
   <data name="NoQueryStrings" xml:space="preserve">
     <value>There is no query string because the in-memory provider does not use a string-based query language.</value>
   </data>

src/EFCore.InMemory/Query/Internal/InMemoryQueryTranslationPreprocessor.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.EntityFrameworkCore.InMemory.Internal;
+using System.Linq.Expressions;
+
+namespace Microsoft.EntityFrameworkCore.InMemory.Query.Internal;
+
+/// <summary>
+///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+///     any release. You should only use it directly in your code with extreme caution and knowing that
+///     doing so can result in application failures when updating to a new Entity Framework Core release.
+/// </summary>
+public class InMemoryQueryTranslationPreprocessor : QueryTranslationPreprocessor
+{
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public InMemoryQueryTranslationPreprocessor(
+        QueryTranslationPreprocessorDependencies dependencies,
+        QueryCompilationContext queryCompilationContext)
+        : base(dependencies, queryCompilationContext)
+    {
+    }
+
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public override Expression Process(Expression query)
+    {
+        var result = base.Process(query);
+
+        if (result is MethodCallExpression methodCallExpression
+            && methodCallExpression.Method.IsGenericMethod
+            && (methodCallExpression.Method.GetGenericMethodDefinition() == QueryableMethods.GroupByWithKeySelector
+                || methodCallExpression.Method.GetGenericMethodDefinition() == QueryableMethods.GroupByWithKeyElementSelector))
+        {
+            throw new InvalidOperationException(
+                CoreStrings.TranslationFailedWithDetails(methodCallExpression.Print(), InMemoryStrings.NonComposedGroupByNotSupported));
+        }
+
+        return result;
+    }
+}

src/EFCore.InMemory/Query/Internal/InMemoryQueryTranslationPreprocessorFactory.cs

@@ -0,0 +1,39 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace Microsoft.EntityFrameworkCore.InMemory.Query.Internal;
+
+/// <summary>
+///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+///     any release. You should only use it directly in your code with extreme caution and knowing that
+///     doing so can result in application failures when updating to a new Entity Framework Core release.
+/// </summary>
+public class InMemoryQueryTranslationPreprocessorFactory : IQueryTranslationPreprocessorFactory
+{
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public InMemoryQueryTranslationPreprocessorFactory(
+        QueryTranslationPreprocessorDependencies dependencies)
+    {
+        Dependencies = dependencies;
+    }
+
+    /// <summary>
+    ///     Dependencies for this service.
+    /// </summary>
+    protected virtual QueryTranslationPreprocessorDependencies Dependencies { get; }
+
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    public virtual QueryTranslationPreprocessor Create(QueryCompilationContext queryCompilationContext)
+        => new InMemoryQueryTranslationPreprocessor(Dependencies, queryCompilationContext);
+}