Allow creation of a DbCommand from an EF IQueryable

Provides access to all the real parameter values, including facets. Should be executable.

However, pretty sure people will think this isn't a good idea...

src/EFCore.Relational/Extensions/RelationalQueryableExtensions.cs

@@ -2,10 +2,13 @@
 // 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.Data.Common;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
 using JetBrains.Annotations;
+using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Query;
 using Microsoft.EntityFrameworkCore.Utilities;
 
@@ -17,6 +20,39 @@ namespace Microsoft.EntityFrameworkCore
     /// </summary>
     public static class RelationalQueryableExtensions
     {
+        /// <summary>
+        ///     <para>
+        ///         Creates a <see cref="DbCommand"/> set up to execute this query.
+        ///     </para>
+        ///     <para>
+        ///         This is only typically supported by queries generated by Entity Framework Core.
+        ///     </para>
+        ///     <para>
+        ///         Warning: there is no guarantee that executing this command directly will result in the same behavior as if EF Core had
+        ///         executed the command.
+        ///     </para>
+        ///     <para>
+        ///         Note that DbCommand is an <see cref="IDisposable"/> object. The caller is responsible for disposing the returned
+        ///         command.
+        ///     </para>
+        ///     <para>
+        ///         This is only typically supported by queries generated by Entity Framework Core.
+        ///     </para>
+        /// </summary>
+        /// <param name="source"> The query source. </param>
+        /// <returns> The query string for debugging. </returns>
+        public static DbCommand CreateDbCommand([NotNull] this IQueryable source)
+        {
+            Check.NotNull(source, nameof(source));
+
+            if (source.Provider.Execute<IEnumerable>(source.Expression) is IRelationalQueryingEnumerable queryingEnumerable)
+            {
+                return queryingEnumerable.CreateDbCommand();
+            }
+
+            throw new NotSupportedException(RelationalStrings.NoDbCommand);
+        }
+
         internal static readonly MethodInfo FromSqlOnQueryableMethodInfo
             = typeof(RelationalQueryableExtensions)
                 .GetTypeInfo().GetDeclaredMethods(nameof(FromSqlOnQueryable))

src/EFCore.Relational/Properties/RelationalStrings.resx

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!-- 
-    Microsoft ResX Schema 
-    
+  <!--
+    Microsoft ResX Schema
+
     Version 2.0
-    
-    The primary goals of this format is to allow a simple XML format 
-    that is mostly human readable. The generation and parsing of the 
-    various data types are done through the TypeConverter classes 
+
+    The primary goals of this format is to allow a simple XML format
+    that is mostly human readable. The generation and parsing of the
+    various data types are done through the TypeConverter classes
     associated with the data types.
-    
+
     Example:
-    
+
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-                
-    There are any number of "resheader" rows that contain simple 
+
+    There are any number of "resheader" rows that contain simple
     name/value pairs.
-    
-    Each data row contains a name, and value. The row also contains a 
-    type or mimetype. Type corresponds to a .NET class that support 
-    text/value conversion through the TypeConverter architecture. 
-    Classes that don't support this are serialized and stored with the 
+
+    Each data row contains a name, and value. The row also contains a
+    type or mimetype. Type corresponds to a .NET class that support
+    text/value conversion through the TypeConverter architecture.
+    Classes that don't support this are serialized and stored with the
     mimetype set.
-    
-    The mimetype is used for serialized objects, and tells the 
-    ResXResourceReader how to depersist the object. This is currently not 
+
+    The mimetype is used for serialized objects, and tells the
+    ResXResourceReader how to depersist the object. This is currently not
     extensible. For a given mimetype the value must be set accordingly:
-    
-    Note - application/x-microsoft.net.object.binary.base64 is the format 
-    that the ResXResourceWriter will generate, however the reader can 
+
+    Note - application/x-microsoft.net.object.binary.base64 is the format
+    that the ResXResourceWriter will generate, however the reader can
     read any of the formats listed below.
-    
+
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with 
+    value   : The object must be serialized with
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-    
+
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with 
+    value   : The object must be serialized with
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array 
+    value   : The object must be serialized into a byte array
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -120,6 +120,9 @@
   <data name="ModificationCommandInvalidEntityState" xml:space="preserve">
     <value>Cannot save changes for an entity in state '{entityState}'.</value>
   </data>
+  <data name="NoDbCommand" xml:space="preserve">
+    <value>Cannot create a 'DbCommand' for a non-relational query.</value>
+  </data>
   <data name="UpdateConcurrencyException" xml:space="preserve">
     <value>Database operation expected to affect {expectedRows} row(s) but actually affected {actualRows} row(s). Data may have been modified or deleted since entities were loaded. See http://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.</value>
   </data>

src/EFCore.Relational/Query/IRelationalQueryingEnumerable.cs

@@ -0,0 +1,38 @@
+// 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.Data.Common;
+
+namespace Microsoft.EntityFrameworkCore.Query
+{
+    /// <summary>
+    ///     <para>
+    ///         Interface that can be implemented by a database provider's <see cref="IEnumerable" /> implementation to
+    ///         provide the query string for debugging purposes.
+    ///     </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 IRelationalQueryingEnumerable : IQueryingEnumerable
+    {
+        /// <summary>
+        ///     <para>
+        ///         Creates a <see cref="DbCommand"/> set up to execute this query.
+        ///     </para>
+        ///     <para>
+        ///         Warning: there is no guarantee that executing this command directly will result in the same behavior as if EF Core had
+        ///         executed the command.
+        ///     </para>
+        ///     <para>
+        ///         Note that DbCommand is an <see cref="IDisposable"/> object. The caller is responsible for disposing the returned
+        ///         command.
+        ///     </para>
+        /// </summary>
+        /// <returns> The newly created command. </returns>
+        DbCommand CreateDbCommand();
+    }
+}

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

@@ -22,7 +22,7 @@ namespace Microsoft.EntityFrameworkCore.Query.Internal
     ///     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 QueryingEnumerable<T> : IEnumerable<T>, IAsyncEnumerable<T>, IQueryingEnumerable
+    public class QueryingEnumerable<T> : IEnumerable<T>, IAsyncEnumerable<T>, IRelationalQueryingEnumerable
     {
         private readonly RelationalQueryContext _relationalQueryContext;
         private readonly RelationalCommandCache _relationalCommandCache;
@@ -87,9 +87,8 @@ public virtual IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken cancella
         ///     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 ToQueryString()
-        {
-            using var command = _relationalCommandCache
+        public virtual DbCommand CreateDbCommand()
+            => _relationalCommandCache
                 .GetRelationalCommand(_relationalQueryContext.ParameterValues)
                 .CreateCommand(
                     new RelationalCommandParameterObject(
@@ -101,6 +100,16 @@ public virtual string ToQueryString()
                     Guid.Empty,
                     (DbCommandMethod)(-1));
 
+        /// <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 ToQueryString()
+        {
+            using var command = CreateDbCommand();
+
             if (command.Parameters.Count == 0)
             {
                 return command.CommandText;

src/EFCore/Query/IQueryingEnumerable.cs

@@ -11,15 +11,19 @@ namespace Microsoft.EntityFrameworkCore.Query
     ///         provide the query string for debugging purposes.
     ///     </para>
     ///     <para>
-    ///         This method is typically used by database providers (and other extensions). It is generally
+    ///         This interface is typically used by database providers (and other extensions). It is generally
     ///         not used in application code.
     ///     </para>
     /// </summary>
     public interface IQueryingEnumerable
     {
         /// <summary>
-        ///     A string representation of the query used. This string may not be suitable for direct execution is intended only
-        ///     for use in debugging.
+        ///     <para>
+        ///         A string representation of the query used.
+        ///     </para>
+        ///     <para>
+        ///         Warning: this string may not be suitable for direct execution is intended only for use in debugging.
+        ///     </para>
         /// </summary>
         /// <returns> The query string. </returns>
         string ToQueryString();