Can we run it? Yes we can!

Design meeting feedback on #19334 for #6482

* Formatting of the relational query string can now be overridden by providers
* SQL Server overrides this to create runnable `Parameter` declarations
* Tested by:
  * Executing the DbCommand we create when using `CreateDbCommand`
  * Executing a DbCommand created externally and given the generated query string

src/EFCore.Relational/Extensions/RelationalQueryableExtensions.cs

@@ -10,6 +10,7 @@
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Query;
+using Microsoft.EntityFrameworkCore.Query.Internal;
 using Microsoft.EntityFrameworkCore.Utilities;
 
 // ReSharper disable once CheckNamespace

src/EFCore.Relational/Infrastructure/EntityFrameworkRelationalServicesBuilder.cs

@@ -72,6 +72,7 @@ public static readonly IDictionary<Type, ServiceCharacteristics> RelationalServi
                 { typeof(IMethodCallTranslatorProvider), new ServiceCharacteristics(ServiceLifetime.Singleton) },
                 { typeof(IMemberTranslatorProvider), new ServiceCharacteristics(ServiceLifetime.Singleton) },
                 { typeof(ISqlExpressionFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
+                { typeof(IRelationalQueryStringFactory), new ServiceCharacteristics(ServiceLifetime.Singleton) },
                 { typeof(ICommandBatchPreparer), new ServiceCharacteristics(ServiceLifetime.Scoped) },
                 { typeof(IModificationCommandBatchFactory), new ServiceCharacteristics(ServiceLifetime.Scoped) },
                 { typeof(IMigrationsModelDiffer), new ServiceCharacteristics(ServiceLifetime.Scoped) },
@@ -167,6 +168,7 @@ public override EntityFrameworkServicesBuilder TryAddCoreServices()
             TryAdd<ISqlExpressionFactory, SqlExpressionFactory>();
             TryAdd<IQueryTranslationPreprocessorFactory, RelationalQueryTranslationPreprocessorFactory>();
             TryAdd<IRelationalParameterBasedQueryTranslationPostprocessorFactory, RelationalParameterBasedQueryTranslationPostprocessorFactory>();
+            TryAdd<IRelationalQueryStringFactory, RelationalQueryStringFactory>();
 
             ServiceCollectionMap.GetInfrastructure()
                 .AddDependencySingleton<RelationalSqlGenerationHelperDependencies>()

src/EFCore.Relational/Query/IRelationalQueryStringFactory.cs

@@ -0,0 +1,27 @@
+// 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.Data.Common;
+using JetBrains.Annotations;
+
+namespace Microsoft.EntityFrameworkCore.Query
+{
+    /// <summary>
+    ///     <para>
+    ///         Implemented by database providers to generate the query string for <see cref="EntityFrameworkQueryableExtensions.ToQueryString" />.
+    ///     </para>
+    ///     <para>
+    ///         This interface is typically used by database providers (and other extensions). It is generally
+    ///         not used in application code.
+    ///     </para>
+    /// </summary>
+    public interface IRelationalQueryStringFactory
+    {
+        /// <summary>
+        ///     Returns a formatted query string for the given command.
+        /// </summary>
+        /// <param name="command"> The command that represents the query. </param>
+        /// <returns> The formatted string. </returns>
+        string Create([NotNull] DbCommand command);
+    }
+}

src/EFCore.Relational/Query/Internal/IRelationalQueryingEnumerable.cs

@@ -0,0 +1,24 @@
+// 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.Data.Common;
+
+namespace Microsoft.EntityFrameworkCore.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 interface IRelationalQueryingEnumerable : IQueryingEnumerable
+    {
+        /// <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>
+        DbCommand CreateDbCommand();
+    }
+}

src/EFCore.Relational/Query/Internal/QueryingEnumerable.cs

@@ -6,13 +6,11 @@
 using System.Collections.Generic;
 using System.Data.Common;
 using System.Linq;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Storage;
-using Microsoft.EntityFrameworkCore.Storage.Internal;
 
 namespace Microsoft.EntityFrameworkCore.Query.Internal
 {
@@ -107,22 +105,7 @@ public virtual DbCommand CreateDbCommand()
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
         public virtual string ToQueryString()
-        {
-            using var command = CreateDbCommand();
-
-            if (command.Parameters.Count == 0)
-            {
-                return command.CommandText;
-            }
-
-            var builder = new StringBuilder();
-            foreach (var parameter in command.Parameters.FormatParameterList(logParameterValues: true))
-            {
-                builder.Append("-- ").AppendLine(parameter);
-            }
-
-            return builder.Append(command.CommandText).ToString();
-        }
+            => _relationalQueryContext.RelationalQueryStringFactory.Create(CreateDbCommand());
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore.Relational/Query/Internal/RelationalQueryStringFactory.cs

@@ -0,0 +1,40 @@
+// 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.Data.Common;
+using System.Text;
+using Microsoft.EntityFrameworkCore.Storage.Internal;
+
+namespace Microsoft.EntityFrameworkCore.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 RelationalQueryStringFactory : IRelationalQueryStringFactory
+    {
+        /// <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 string Create(DbCommand command)
+        {
+            if (command.Parameters.Count == 0)
+            {
+                return command.CommandText;
+            }
+
+            var builder = new StringBuilder();
+            foreach (DbParameter parameter in command.Parameters)
+            {
+                builder.Append("-- ").AppendLine(parameter.FormatParameter(logParameterValues: true));
+            }
+
+            return builder.Append(command.CommandText).ToString();
+        }
+    }
+}

src/EFCore.Relational/Query/RelationalQueryContext.cs

@@ -1,6 +1,7 @@
 // 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.Data.Common;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Storage;
 using Microsoft.EntityFrameworkCore.Utilities;
@@ -38,6 +39,12 @@ public RelationalQueryContext(
         /// </summary>
         protected virtual RelationalQueryContextDependencies RelationalDependencies { get; }
 
+        /// <summary>
+        ///     A factory for creating a readable query string from a <see cref="DbCommand"/>
+        /// </summary>
+        public virtual IRelationalQueryStringFactory RelationalQueryStringFactory
+            => RelationalDependencies.RelationalQueryStringFactory;
+
         /// <summary>
         ///     Gets the active relational connection.
         /// </summary>

src/EFCore.Relational/Query/RelationalQueryContextDependencies.cs

@@ -1,6 +1,7 @@
 // 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.Data.Common;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Infrastructure;
 using Microsoft.EntityFrameworkCore.Storage;
@@ -55,24 +56,40 @@ public sealed class RelationalQueryContextDependencies
         /// </summary>
         [EntityFrameworkInternal]
         public RelationalQueryContextDependencies(
-            [NotNull] IRelationalConnection relationalConnection)
+            [NotNull] IRelationalConnection relationalConnection,
+            [NotNull] IRelationalQueryStringFactory relationalQueryStringFactory)
         {
             Check.NotNull(relationalConnection, nameof(relationalConnection));
+            Check.NotNull(relationalQueryStringFactory, nameof(relationalQueryStringFactory));
 
             RelationalConnection = relationalConnection;
+            RelationalQueryStringFactory = relationalQueryStringFactory;
         }
 
         /// <summary>
         ///     The connection.
         /// </summary>
         public IRelationalConnection RelationalConnection { get; }
 
+        /// <summary>
+        ///     A factory for creating a readable query string from a <see cref="DbCommand"/>
+        /// </summary>
+        public IRelationalQueryStringFactory RelationalQueryStringFactory { get; }
+
         /// <summary>
         ///     Clones this dependency parameter object with one service replaced.
         /// </summary>
         /// <param name="relationalConnection"> A replacement for the current dependency of this type. </param>
         /// <returns> A new parameter object with the given service replaced. </returns>
         public RelationalQueryContextDependencies With([NotNull] IRelationalConnection relationalConnection)
-            => new RelationalQueryContextDependencies(relationalConnection);
+            => new RelationalQueryContextDependencies(relationalConnection, RelationalQueryStringFactory);
+
+        /// <summary>
+        ///     Clones this dependency parameter object with one service replaced.
+        /// </summary>
+        /// <param name="relationalQueryStringFactory"> A replacement for the current dependency of this type. </param>
+        /// <returns> A new parameter object with the given service replaced. </returns>
+        public RelationalQueryContextDependencies With([NotNull] IRelationalQueryStringFactory relationalQueryStringFactory)
+            => new RelationalQueryContextDependencies(RelationalConnection, relationalQueryStringFactory);
     }
 }

src/EFCore.Relational/Storage/Internal/DbParameterCollectionExtensions.cs

@@ -31,32 +31,27 @@ public static class DbParameterCollectionExtensions
         public static string FormatParameters(
             [NotNull] this DbParameterCollection parameters,
             bool logParameterValues)
-            => FormatParameterList(parameters, logParameterValues).Join();
+            => parameters
+                .Cast<DbParameter>()
+                .Select(p => FormatParameter(p, logParameterValues)).Join();
 
         /// <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 static IEnumerable<string> FormatParameterList(
-            [NotNull] this DbParameterCollection parameters,
-            bool logParameterValues)
-        {
-            return parameters
-                .Cast<DbParameter>()
-                .Select(
-                    p => FormatParameter(
-                        p.ParameterName,
-                        logParameterValues ? p.Value : "?",
-                        logParameterValues,
-                        p.Direction,
-                        p.DbType,
-                        p.IsNullable,
-                        p.Size,
-                        p.Precision,
-                        p.Scale));
-        }
+        public static string FormatParameter([NotNull] this DbParameter parameter, bool logParameterValues)
+            => FormatParameter(
+                parameter.ParameterName,
+                logParameterValues ? parameter.Value : "?",
+                logParameterValues,
+                parameter.Direction,
+                parameter.DbType,
+                parameter.IsNullable,
+                parameter.Size,
+                parameter.Precision,
+                parameter.Scale);
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to

src/EFCore.SqlServer/Extensions/SqlServerServiceCollectionExtensions.cs

@@ -68,6 +68,7 @@ public static IServiceCollection AddEntityFrameworkSqlServer([NotNull] this ISer
                 .TryAdd<IRelationalDatabaseCreator, SqlServerDatabaseCreator>()
                 .TryAdd<IHistoryRepository, SqlServerHistoryRepository>()
                 .TryAdd<IExecutionStrategyFactory, SqlServerExecutionStrategyFactory>()
+                .TryAdd<IRelationalQueryStringFactory, SqlServerQueryStringFactory>()
 
                 // New Query Pipeline
                 .TryAdd<IMethodCallTranslatorProvider, SqlServerMethodCallTranslatorProvider>()