Implement GROUP BY

src/EFCore.Relational.Specification.Tests/QueryNoClientEvalTestBase.cs

@@ -66,7 +66,7 @@ public virtual void Throws_when_where_subquery_correlated()
                 Assert.Equal(CoreStrings.WarningAsErrorTemplate(
                         $"{nameof(RelationalEventId)}.{nameof(RelationalEventId.QueryClientEvaluationWarning)}",
                         RelationalStrings.ClientEvalWarning(
-                            "{from Customer c2 in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[Microsoft.EntityFrameworkCore.Specification.Tests.TestModels.Northwind.Customer]) where (([c1].CustomerID == [c2].CustomerID) AndAlso [c2].IsLondon) select [c2] => Any()}")),
+                            "[c2].IsLondon")),
                     Assert.Throws<InvalidOperationException>(
                         () => context.Customers
                             .Where(c1 => context.Customers

src/EFCore.Relational/Query/ExpressionVisitors/Internal/GroupingShaper.cs

@@ -0,0 +1,85 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reflection;
+using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.Storage;
+using Remotion.Linq.Clauses.ResultOperators;
+
+namespace Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.Internal
+{
+    /// <summary>
+    ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+    ///     directly from your code. This API may change or be removed in future releases.
+    /// </summary>
+    public class GroupingShaper : Shaper, IShaper<IGrouping<ValueBuffer, ValueBuffer>>
+    {
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public GroupingShaper([NotNull] GroupResultOperator groupResultOperator)
+            : base(groupResultOperator)
+        {
+        }
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public override Type Type => typeof(IGrouping<ValueBuffer, ValueBuffer>);
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public virtual IGrouping<ValueBuffer, ValueBuffer> Shape(QueryContext queryContext, ValueBuffer valueBuffer)
+        {
+            return new ValueBufferGrouping(valueBuffer);
+        }
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public override Shaper WithOffset(int offset) => this;
+
+        /// <summary>
+        ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
+        ///     directly from your code. This API may change or be removed in future releases.
+        /// </summary>
+        public static Expression CreateValueBufferAccessExpression(
+            [NotNull] Expression valueBufferGroupingExpression)
+        {
+            return Expression.MakeMemberAccess(
+                Expression.Convert(
+                    valueBufferGroupingExpression,
+                    typeof(ValueBufferGrouping)),
+                _valueBufferGroupingValueBufferProperty);
+        }
+
+        private static readonly PropertyInfo _valueBufferGroupingValueBufferProperty
+            = typeof(ValueBufferGrouping).GetTypeInfo().GetDeclaredProperty("ValueBuffer");
+
+        private struct ValueBufferGrouping : IGrouping<ValueBuffer, ValueBuffer>
+        {
+            public ValueBufferGrouping(ValueBuffer valueBuffer)
+            {
+                ValueBuffer = valueBuffer;
+            }
+
+            public ValueBuffer ValueBuffer { get; }
+
+            public ValueBuffer Key => ValueBuffer;
+
+            public IEnumerator<ValueBuffer> GetEnumerator() => Enumerable.Repeat(ValueBuffer, 1).GetEnumerator();
+
+            IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+        }
+    }
+}

src/EFCore.Relational/Query/ExpressionVisitors/RelationalEntityQueryableExpressionVisitor.cs

@@ -32,6 +32,7 @@ public class RelationalEntityQueryableExpressionVisitor : EntityQueryableExpress
         private readonly IMaterializerFactory _materializerFactory;
         private readonly IShaperCommandContextFactory _shaperCommandContextFactory;
         private readonly IRelationalAnnotationProvider _relationalAnnotationProvider;
+        private readonly ISqlTranslatingExpressionVisitorFactory _sqlTranslatingExpressionVisitorFactory;
         private readonly IQuerySource _querySource;
 
         /// <summary>
@@ -53,6 +54,7 @@ public RelationalEntityQueryableExpressionVisitor(
             _materializerFactory = dependencies.MaterializerFactory;
             _shaperCommandContextFactory = dependencies.ShaperCommandContextFactory;
             _relationalAnnotationProvider = dependencies.RelationalAnnotationProvider;
+            _sqlTranslatingExpressionVisitorFactory = dependencies.SqlTranslatingExpressionVisitorFactory;
             _querySource = querySource;
         }
 
@@ -92,6 +94,11 @@ protected override Expression VisitMember(MemberExpression node)
         {
             Check.NotNull(node, nameof(node));
 
+            if (TryHandleGroupingKeyExpression(node))
+            {
+                return node;
+            }
+
             QueryModelVisitor
                 .BindMemberExpression(
                     node,
@@ -105,6 +112,46 @@ protected override Expression VisitMember(MemberExpression node)
             return base.VisitMember(node);
         }
 
+        private bool TryHandleGroupingKeyExpression(MemberExpression node)
+        {
+            if (node.Expression == null || !node.Expression.Type.IsGrouping() || node.Member.Name != "Key")
+            {
+                return false;
+            }
+
+            var groupedQuerySource = node.Expression.TryGetQuerySource();
+
+            if (groupedQuerySource == null)
+            {
+                return false;
+            }
+
+            var targetSelectExpression = QueryModelVisitor.TryGetQuery(groupedQuerySource);
+
+            if (targetSelectExpression == null)
+            {
+                return false;
+            }
+
+            var sqlTranslator = _sqlTranslatingExpressionVisitorFactory.Create(QueryModelVisitor);
+            var sqlExpression = sqlTranslator.Visit(node);
+
+            if (sqlExpression is CompositeExpression compositeExpression)
+            {
+                foreach (var expression in compositeExpression.Flatten())
+                {
+                    targetSelectExpression.AddToProjection(
+                        targetSelectExpression.RetargetProjectionExpression(
+                            expression, 
+                            groupedQuerySource));
+                }
+
+                return true;
+            }
+
+            return false;
+        }
+
         /// <summary>
         ///     Visit a method call expression.
         /// </summary>

src/EFCore.Relational/Query/ExpressionVisitors/RelationalEntityQueryableExpressionVisitorDependencies.cs

@@ -48,24 +48,28 @@ public sealed class RelationalEntityQueryableExpressionVisitorDependencies
         /// <param name="materializerFactory"> The materializer factory. </param>
         /// <param name="shaperCommandContextFactory"> The shaper command context factory. </param>
         /// <param name="relationalAnnotationProvider"> The relational annotation provider. </param>
+        /// <param name="sqlTranslatingExpressionVisitorFactory"> The SQL translating expression visitor factory. </param>
         public RelationalEntityQueryableExpressionVisitorDependencies(
             [NotNull] IModel model,
             [NotNull] ISelectExpressionFactory selectExpressionFactory,
             [NotNull] IMaterializerFactory materializerFactory,
             [NotNull] IShaperCommandContextFactory shaperCommandContextFactory,
-            [NotNull] IRelationalAnnotationProvider relationalAnnotationProvider)
+            [NotNull] IRelationalAnnotationProvider relationalAnnotationProvider,
+            [NotNull] ISqlTranslatingExpressionVisitorFactory sqlTranslatingExpressionVisitorFactory)
         {
             Check.NotNull(model, nameof(model));
             Check.NotNull(selectExpressionFactory, nameof(selectExpressionFactory));
             Check.NotNull(materializerFactory, nameof(materializerFactory));
             Check.NotNull(shaperCommandContextFactory, nameof(shaperCommandContextFactory));
             Check.NotNull(relationalAnnotationProvider, nameof(relationalAnnotationProvider));
+            Check.NotNull(sqlTranslatingExpressionVisitorFactory, nameof(sqlTranslatingExpressionVisitorFactory));
 
             Model = model;
             SelectExpressionFactory = selectExpressionFactory;
             MaterializerFactory = materializerFactory;
             ShaperCommandContextFactory = shaperCommandContextFactory;
             RelationalAnnotationProvider = relationalAnnotationProvider;
+            SqlTranslatingExpressionVisitorFactory = sqlTranslatingExpressionVisitorFactory;
         }
 
         /// <summary>
@@ -93,6 +97,11 @@ public RelationalEntityQueryableExpressionVisitorDependencies(
         /// </summary>
         public IRelationalAnnotationProvider RelationalAnnotationProvider { get; }
 
+        /// <summary>
+        ///     The SQL translating expression visitor factory.
+        /// </summary>
+        public ISqlTranslatingExpressionVisitorFactory SqlTranslatingExpressionVisitorFactory { get; }
+
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
         /// </summary>
@@ -104,7 +113,8 @@ public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] IMo
                 SelectExpressionFactory,
                 MaterializerFactory,
                 ShaperCommandContextFactory,
-                RelationalAnnotationProvider);
+                RelationalAnnotationProvider,
+                SqlTranslatingExpressionVisitorFactory);
 
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
@@ -117,7 +127,8 @@ public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] ISe
                 selectExpressionFactory,
                 MaterializerFactory,
                 ShaperCommandContextFactory,
-                RelationalAnnotationProvider);
+                RelationalAnnotationProvider,
+                SqlTranslatingExpressionVisitorFactory);
 
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
@@ -130,7 +141,8 @@ public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] IMa
                 SelectExpressionFactory,
                 materializerFactory,
                 ShaperCommandContextFactory,
-                RelationalAnnotationProvider);
+                RelationalAnnotationProvider,
+                SqlTranslatingExpressionVisitorFactory);
 
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
@@ -143,7 +155,8 @@ public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] ISh
                 SelectExpressionFactory,
                 MaterializerFactory,
                 shaperCommandContextFactory,
-                RelationalAnnotationProvider);
+                RelationalAnnotationProvider,
+                SqlTranslatingExpressionVisitorFactory);
 
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
@@ -156,6 +169,21 @@ public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] IRe
                 SelectExpressionFactory,
                 MaterializerFactory,
                 ShaperCommandContextFactory,
-                relationalAnnotationProvider);
+                relationalAnnotationProvider,
+                SqlTranslatingExpressionVisitorFactory);
+
+        /// <summary>
+        ///     Clones this dependency parameter object with one service replaced.
+        /// </summary>
+        /// <param name="sqlTranslatingExpressionVisitorFactory"> A replacement for the current dependency of this type. </param>
+        /// <returns> A new parameter object with the given service replaced. </returns>
+        public RelationalEntityQueryableExpressionVisitorDependencies With([NotNull] ISqlTranslatingExpressionVisitorFactory sqlTranslatingExpressionVisitorFactory)
+            => new RelationalEntityQueryableExpressionVisitorDependencies(
+                Model,
+                SelectExpressionFactory,
+                MaterializerFactory,
+                ShaperCommandContextFactory,
+                RelationalAnnotationProvider,
+                sqlTranslatingExpressionVisitorFactory);
     }
 }