Add hooks for expression fragments and visitors

Creates Npgsql implementations of `IExpressionFragmentTranslator`
and `IQueryOptimizer` to support more complex translations.

These classes make it easier to inject new fragment translations
and expression rewrites into the EF Core translation process.

This is split out from #431. Working examples can be found there.

src/EFCore.PG/Extensions/NpgsqlServiceCollectionExtensions.cs

@@ -51,6 +51,7 @@
 // ReSharper disable once CheckNamespace
 namespace Microsoft.Extensions.DependencyInjection
 {
+    // ReSharper disable once UnusedMember.Global
     public static class NpgsqlEntityFrameworkServicesBuilderExtensions
     {
         /// <summary>
@@ -106,6 +107,8 @@ public static IServiceCollection AddEntityFrameworkNpgsql([NotNull] this IServic
                 .TryAdd<IQueryCompilationContextFactory, NpgsqlQueryCompilationContextFactory>()
                 .TryAdd<IMemberTranslator, NpgsqlCompositeMemberTranslator>()
                 .TryAdd<ICompositeMethodCallTranslator, NpgsqlCompositeMethodCallTranslator>()
+                .TryAdd<IExpressionFragmentTranslator, NpgsqlCompositeExpressionFragmentTranslator>()
+                .TryAdd<IQueryOptimizer, NpgsqlQueryOptimizer>()
                 .TryAdd<IQuerySqlGeneratorFactory, NpgsqlQuerySqlGeneratorFactory>()
                 .TryAdd<ISqlTranslatingExpressionVisitorFactory, NpgsqlSqlTranslatingExpressionVisitorFactory>()
                 .TryAdd<ISingletonOptions, INpgsqlOptions>(p => p.GetService<INpgsqlOptions>())

src/EFCore.PG/Query/ExpressionTranslators/Internal/NpgsqlCompositeExpressionFragmentTranslator.cs

@@ -0,0 +1,58 @@
+#region License
+
+// The PostgreSQL License
+//
+// Copyright (C) 2016 The Npgsql Development Team
+//
+// Permission to use, copy, modify, and distribute this software and its
+// documentation for any purpose, without fee, and without a written
+// agreement is hereby granted, provided that the above copyright notice
+// and this paragraph and the following two paragraphs appear in all copies.
+//
+// IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
+// FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+// INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+// DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
+// THE POSSIBILITY OF SUCH DAMAGE.
+//
+// THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+// ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
+// TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+
+#endregion
+
+using System.Collections.Generic;
+using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.Query.ExpressionTranslators;
+
+namespace Npgsql.EntityFrameworkCore.PostgreSQL.Query.ExpressionTranslators.Internal
+{
+    /// <summary>
+    /// A composite expression fragment translator that dispatches to multiple specialized translators specific to Npgsql.
+    /// </summary>
+    public class NpgsqlCompositeExpressionFragmentTranslator : RelationalCompositeExpressionFragmentTranslator
+    {
+        /// <summary>
+        /// The default expression fragment translators registered by the Npgsql provider.
+        /// </summary>
+        [NotNull] [ItemNotNull] static readonly IExpressionFragmentTranslator[] ExpressionFragmentTranslators = {};
+
+        /// <inheritdoc />
+        public NpgsqlCompositeExpressionFragmentTranslator(
+            [NotNull] RelationalCompositeExpressionFragmentTranslatorDependencies dependencies)
+            : base(dependencies)
+        {
+            // ReSharper disable once DoNotCallOverridableMethodsInConstructor
+            AddTranslators(ExpressionFragmentTranslators);
+        }
+
+        /// <summary>
+        /// Adds additional dispatches to the translators list.
+        /// </summary>
+        /// <param name="translators">The translators.</param>
+        public new virtual void AddTranslators([NotNull] IEnumerable<IExpressionFragmentTranslator> translators)
+            => base.AddTranslators(translators);
+    }
+}

src/EFCore.PG/Query/Internal/NpgsqlQueryOptimizer.cs

@@ -0,0 +1,55 @@
+#region License
+
+// The PostgreSQL License
+//
+// Copyright (C) 2016 The Npgsql Development Team
+//
+// Permission to use, copy, modify, and distribute this software and its
+// documentation for any purpose, without fee, and without a written
+// agreement is hereby granted, provided that the above copyright notice
+// and this paragraph and the following two paragraphs appear in all copies.
+//
+// IN NO EVENT SHALL THE NPGSQL DEVELOPMENT TEAM BE LIABLE TO ANY PARTY
+// FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
+// INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
+// DOCUMENTATION, EVEN IF THE NPGSQL DEVELOPMENT TEAM HAS BEEN ADVISED OF
+// THE POSSIBILITY OF SUCH DAMAGE.
+//
+// THE NPGSQL DEVELOPMENT TEAM SPECIFICALLY DISCLAIMS ANY WARRANTIES,
+// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
+// ON AN "AS IS" BASIS, AND THE NPGSQL DEVELOPMENT TEAM HAS NO OBLIGATIONS
+// TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+
+#endregion
+
+using System.Linq.Expressions;
+using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
+using Remotion.Linq;
+
+namespace Npgsql.EntityFrameworkCore.PostgreSQL.Query.Internal
+{
+    /// <summary>
+    /// The default relational LINQ query optimizer for Npgsql.
+    /// </summary>
+    public class NpgsqlQueryOptimizer : QueryOptimizer
+    {
+        /// <summary>
+        /// The default expression visitors registered by the Npgsql provider.
+        /// </summary>
+        [NotNull] [ItemNotNull] static readonly ExpressionVisitor[] ExpressionVisitors = {};
+
+        /// <inheritdoc />
+        public override void Optimize(QueryCompilationContext queryCompilationContext, QueryModel queryModel)
+        {
+            base.Optimize(queryCompilationContext, queryModel);
+
+            for (int i = 0; i < ExpressionVisitors.Length; i++)
+            {
+                queryModel.TransformExpressions(ExpressionVisitors[i].Visit);
+            }
+        }
+    }
+}