Reintroduce legacy support to emulate row skipping in the most outer SELECT statement, by letting JetDataReader ignore returned rows.

src/EFCore.Jet/Infrastructure/Internal/IJetOptions.cs

@@ -13,5 +13,6 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
     {
         string ConnectionString { get; }
         DataAccessProviderType DataAccessProviderType { get; }
+        bool UseOuterSelectSkipEmulationViaDataReader { get; }
     }
 }

src/EFCore.Jet/Infrastructure/Internal/JetOptionsExtension.cs

@@ -22,6 +22,7 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
 
         // private bool? _rowNumberPaging;
         private DbProviderFactory _dataAccessProviderFactory;
+        private bool _useOuterSelectSkipEmulationViaDataReader;
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -46,6 +47,7 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
         {
             // _rowNumberPaging = copyFrom._rowNumberPaging;
             _dataAccessProviderFactory = copyFrom._dataAccessProviderFactory;
+            _useOuterSelectSkipEmulationViaDataReader = copyFrom._useOuterSelectSkipEmulationViaDataReader;
         }
 
         /// <summary>
@@ -114,6 +116,29 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
             return clone;
         }
 
+        /// <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 bool UseOuterSelectSkipEmulationViaDataReader => _useOuterSelectSkipEmulationViaDataReader;
+
+        /// <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 JetOptionsExtension WithUseOuterSelectSkipEmulationViaDataReader(bool enabled)
+        {
+            var clone = (JetOptionsExtension) Clone();
+
+            clone._useOuterSelectSkipEmulationViaDataReader = enabled;
+
+            return clone;
+        }
+
         /// <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
@@ -160,6 +185,11 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
                             builder.Append("DataAccessProviderFactory ");
                         }
 
+                        if (Extension._useOuterSelectSkipEmulationViaDataReader)
+                        {
+                            builder.Append("UseOuterSelectSkipEmulationViaDataReader ");
+                        }
+
                         _logFragment = builder.ToString();
                     }
 
@@ -172,7 +202,8 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
                 if (_serviceProviderHash == null)
                 {
                     _serviceProviderHash = (base.GetServiceProviderHashCode() * 397) ^
-                                           (Extension._dataAccessProviderFactory?.GetHashCode() ?? 0L) /* ^
+                                           (Extension._dataAccessProviderFactory?.GetHashCode() ?? 0L) ^
+                                           (Extension._useOuterSelectSkipEmulationViaDataReader.GetHashCode() * 397) /* ^
                                            (Extension._rowNumberPaging?.GetHashCode() ?? 0L)*/;
                 }
 
@@ -185,8 +216,12 @@ namespace EntityFrameworkCore.Jet.Infrastructure.Internal
                 debugInfo["Jet:" + nameof(JetDbContextOptionsBuilder.UseRowNumberForPaging)]
                     = (Extension._rowNumberPaging?.GetHashCode() ?? 0L).ToString(CultureInfo.InvariantCulture);
                 */
-                debugInfo["Jet:" + nameof(JetOptionsExtension.DataAccessProviderFactory)]
+                debugInfo["Jet:" + nameof(DataAccessProviderFactory)]
                     = (Extension._dataAccessProviderFactory?.GetHashCode() ?? 0L).ToString(CultureInfo.InvariantCulture);
+#pragma warning disable 618
+                debugInfo["Jet:" + nameof(JetDbContextOptionsBuilder.UseOuterSelectSkipEmulationViaDataReader)]
+#pragma warning restore 618
+                    = Extension._useOuterSelectSkipEmulationViaDataReader.GetHashCode().ToString(CultureInfo.InvariantCulture);
             }
         }
     }

src/EFCore.Jet/Infrastructure/JetDbContextOptionsBuilder.cs

@@ -40,6 +40,20 @@ namespace EntityFrameworkCore.Jet.Infrastructure
         // public virtual JetDbContextOptionsBuilder UseRowNumberForPaging(bool useRowNumberForPaging = true)
         //    => WithOption(e => e.WithRowNumberPaging(useRowNumberForPaging));
 
+        /// <summary>
+        ///     Jet/ACE doesn't natively support row skipping. When this option is enabled, row skipping will be
+        ///     emulated in the most outer SELECT statement, by letting the JetDataReader ignore as many returned rows
+        ///     as should have been skipped by the database.
+        ///     This will only work when `JetCommand.ExecuteDataReader()` is beeing used to execute the `JetCommand`.
+        ///     It is recommanded to not use this option, but to switch to client evaluation instead, by inserting a
+        ///     call to either `AsEnumerable()`, `AsAsyncEnumerable()`, `ToList()`, or `ToListAsync()` and only then
+        ///     to use `Skip()`. This will work in all cases and independent of the specific `JetCommand.Execute()`
+        ///     method called. 
+        /// </summary>
+        [Obsolete("This method exists for backward compatibility reasons only. Switch to client evaluation instead.")]
+        public virtual JetDbContextOptionsBuilder UseOuterSelectSkipEmulationViaDataReader(bool enabled = true)
+            => WithOption(e => e.WithUseOuterSelectSkipEmulationViaDataReader(enabled));
+
         /// <summary>
         ///     Configures the context to use the default retrying <see cref="IExecutionStrategy" />.
         /// </summary>

src/EFCore.Jet/Internal/JetOptions.cs

@@ -27,6 +27,7 @@ namespace EntityFrameworkCore.Jet.Internal
             // RowNumberPagingEnabled = jetOptions.RowNumberPaging ?? false;
             
             DataAccessProviderType = GetDataAccessProviderTypeFromOptions(jetOptions);
+            UseOuterSelectSkipEmulationViaDataReader = jetOptions.UseOuterSelectSkipEmulationViaDataReader;
             ConnectionString = jetOptions.Connection?.ConnectionString ?? jetOptions.ConnectionString;
         }
 
@@ -55,6 +56,14 @@ namespace EntityFrameworkCore.Jet.Internal
                         nameof(JetOptionsExtension.DataAccessProviderFactory),
                         nameof(DbContextOptionsBuilder.UseInternalServiceProvider)));
             }
+
+            if (UseOuterSelectSkipEmulationViaDataReader != jetOptions.UseOuterSelectSkipEmulationViaDataReader)
+            {
+                throw new InvalidOperationException(
+                    CoreStrings.SingletonOptionChanged(
+                        nameof(JetOptionsExtension.UseOuterSelectSkipEmulationViaDataReader),
+                        nameof(DbContextOptionsBuilder.UseInternalServiceProvider)));
+            }
         }
         
         private static DataAccessProviderType GetDataAccessProviderTypeFromOptions(JetOptionsExtension jetOptions)
@@ -108,6 +117,14 @@ namespace EntityFrameworkCore.Jet.Internal
         /// </summary>
         public virtual DataAccessProviderType DataAccessProviderType { get; private set; }
 
+        /// <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 bool UseOuterSelectSkipEmulationViaDataReader { get; private set; }
+
         /// <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

src/EFCore.Jet/Query/Sql/Internal/JetQuerySqlGenerator.cs

@@ -5,13 +5,12 @@ using System.Collections.Generic;
 using System.Data.Jet;
 using System.Linq;
 using System.Linq.Expressions;
-using System.Text;
+using EntityFrameworkCore.Jet.Infrastructure.Internal;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Storage;
 using EntityFrameworkCore.Jet.Utilities;
 using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Infrastructure;
-using Microsoft.EntityFrameworkCore.Internal;
 using Microsoft.EntityFrameworkCore.Query;
 using Microsoft.EntityFrameworkCore.Query.SqlExpressions;
 
@@ -37,6 +36,7 @@ namespace EntityFrameworkCore.Jet.Query.Sql.Internal
         };
 
         private readonly ITypeMappingSource _typeMappingSource;
+        private readonly IJetOptions _options;
         private readonly JetSqlExpressionFactory _sqlExpressionFactory;
         private readonly ISqlGenerationHelper _sqlGenerationHelper;
         private CoreTypeMapping _boolTypeMapping;
@@ -48,11 +48,13 @@ namespace EntityFrameworkCore.Jet.Query.Sql.Internal
         public JetQuerySqlGenerator(
             [NotNull] QuerySqlGeneratorDependencies dependencies,
             ISqlExpressionFactory sqlExpressionFactory,
-            ITypeMappingSource typeMappingSource)
+            ITypeMappingSource typeMappingSource,
+            IJetOptions options)
             : base(dependencies)
         {
             _sqlExpressionFactory = (JetSqlExpressionFactory) sqlExpressionFactory;
             _typeMappingSource = typeMappingSource;
+            _options = options;
             _sqlGenerationHelper = dependencies.SqlGenerationHelper;
             _boolTypeMapping = _typeMappingSource.FindMapping(typeof(bool));
         }
@@ -350,9 +352,18 @@ namespace EntityFrameworkCore.Jet.Query.Sql.Internal
             Check.NotNull(selectExpression, nameof(selectExpression));
 
             if (selectExpression.Offset != null)
+            {
+                if (_options.UseOuterSelectSkipEmulationViaDataReader)
+                {
+                    Sql.Append("SKIP ");
+                    Visit(selectExpression.Offset);
+                    Sql.Append(" ");
+                }
+                else
                 {
                     throw new InvalidOperationException("Jet does not support skipping rows. Switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync() if needed.");
                 }
+            }
 
             if (selectExpression.Limit != null)
             {

src/EFCore.Jet/Query/Sql/Internal/JetQuerySqlGeneratorFactory.cs

@@ -1,5 +1,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using EntityFrameworkCore.Jet.Infrastructure.Internal;
 using JetBrains.Annotations;
 using Microsoft.EntityFrameworkCore.Query;
 using Microsoft.EntityFrameworkCore.Storage;
@@ -15,6 +16,7 @@ namespace EntityFrameworkCore.Jet.Query.Sql.Internal
         [NotNull] private readonly QuerySqlGeneratorDependencies _dependencies;
         [NotNull] private readonly JetSqlExpressionFactory _sqlExpressionFactory;
         [NotNull] private readonly ITypeMappingSource _typeMappingSource;
+        [NotNull] private readonly IJetOptions _options;
 
         /// <summary>
         ///     This API supports the Entity Framework Core infrastructure and is not intended to be used
@@ -23,14 +25,16 @@ namespace EntityFrameworkCore.Jet.Query.Sql.Internal
         public JetQuerySqlGeneratorFactory(
             [NotNull] QuerySqlGeneratorDependencies dependencies,
             [NotNull] ISqlExpressionFactory sqlExpressionFactory,
-            [NotNull] ITypeMappingSource typeMappingSource)
+            [NotNull] ITypeMappingSource typeMappingSource,
+            [NotNull] IJetOptions options)
         {
             _dependencies = dependencies;
             _sqlExpressionFactory = (JetSqlExpressionFactory)sqlExpressionFactory;
             _typeMappingSource = typeMappingSource;
+            _options = options;
         }
 
         public virtual QuerySqlGenerator Create()
-            => new JetQuerySqlGenerator(_dependencies, _sqlExpressionFactory, _typeMappingSource);
+            => new JetQuerySqlGenerator(_dependencies, _sqlExpressionFactory, _typeMappingSource, _options);
     }
 }

src/System.Data.Jet/JetCommand.cs

@@ -16,8 +16,12 @@ namespace System.Data.Jet
         private readonly JetConnection _connection;
         private JetTransaction _transaction;
         
+        private int _outerSelectSkipEmulationViaDataReaderSkipCount;
+
         private static readonly Regex _createProcedureExpression = new Regex(@"^\s*create\s*procedure\b", RegexOptions.IgnoreCase);
         private static readonly Regex _topParameterRegularExpression = new Regex(@"(?<=(?:^|\s)select\s+top\s+)(?:@\w+|\?)(?=\s)", RegexOptions.IgnoreCase);
+        private static readonly Regex _outerSelectTopValueRegularExpression = new Regex(@"(?<=^\s*select\s+top\s+)\d+(?=\s)", RegexOptions.IgnoreCase);
+        private static readonly Regex _outerSelectSkipValueOrParameterRegularExpression = new Regex(@"(?<=^\s*select)\s+skip\s+(?<SkipValueOrParameter>@\w+|\?|\d+)(?=\s)", RegexOptions.IgnoreCase);
         private static readonly Regex _selectRowCountRegularExpression = new Regex(@"^\s*select\s*@@rowcount\s*;?\s*$", RegexOptions.IgnoreCase);
         private static readonly Regex _ifStatementRegex = new Regex(@"^\s*if\s*(?<not>not)?\s*exists\s*\((?<sqlCheckCommand>.+)\)\s*then\s*(?<sqlCommand>.*)$", RegexOptions.IgnoreCase);
 
@@ -204,10 +208,12 @@ namespace System.Data.Jet
             if ((dataReader = TryGetDataReaderForSelectRowCount(InnerCommand.CommandText)) == null)
             {
                 FixupGlobalVariables();
+                PrepareOuterSelectSkipEmulationViaDataReader();
                 InlineTopParameters();
+                ModifyOuterSelectTopValueForOuterSelectSkipEmulationViaDataReader();
                 FixParameters();
 
-                dataReader = new JetDataReader(InnerCommand.ExecuteReader(behavior));
+                dataReader = new JetDataReader(InnerCommand.ExecuteReader(behavior), _outerSelectSkipEmulationViaDataReaderSkipCount);
 
                 _connection.RowCount = dataReader.RecordsAffected;
             }
@@ -526,6 +532,64 @@ namespace System.Data.Jet
             }
         }
         
+        private void ModifyOuterSelectTopValueForOuterSelectSkipEmulationViaDataReader()
+        {
+            // We modify the TOP clause parameter of the outer most SELECT statement if a SKIP clause was also
+            // specified, because Jet does not support skipping records at all, but we can optionally emulate skipping
+            // behavior for the outer most SELECT statement by controlling how the records are being fetched in
+            // JetDataReader.
+
+            if (_outerSelectSkipEmulationViaDataReaderSkipCount > 0)
+            {
+                InnerCommand.CommandText = _outerSelectTopValueRegularExpression.Replace(
+                    InnerCommand.CommandText,
+                    match => (int.Parse(match.Value) + _outerSelectSkipEmulationViaDataReaderSkipCount).ToString());
+            }
+        }
+
+        private void PrepareOuterSelectSkipEmulationViaDataReader()
+        {
+            // We inline the SKIP clause parameter of the outer most SELECT statement, because Jet does not support
+            // skipping records at all, but we can optionally emulate skipping behavior for the outer most SELECT
+            // statement by controlling how the records are being fetched in JetDataReader.
+
+            var match = _outerSelectSkipValueOrParameterRegularExpression.Match(InnerCommand.CommandText);
+
+            if (!match.Success)
+            {
+                return;
+            }
+
+            var skipValueOrParameter = match.Groups["SkipValueOrParameter"];
+
+            if (IsParameter(skipValueOrParameter.Value))
+            {
+                var parameters = InnerCommand.Parameters.Cast<DbParameter>()
+                    .ToList();
+
+                if (parameters.Count <= 0)
+                {
+                    throw new InvalidOperationException($@"Cannot find ""{skipValueOrParameter.Value}"" parameter for SKIP clause.");
+                }
+
+                var parameter = ExtractParameter(InnerCommand.CommandText, match.Index, parameters);
+                _outerSelectSkipEmulationViaDataReaderSkipCount = Convert.ToInt32(parameter.Value);
+                
+                InnerCommand.Parameters.Clear();
+                InnerCommand.Parameters.AddRange(parameters.ToArray());
+            }
+            else
+            {
+                _outerSelectSkipEmulationViaDataReaderSkipCount = int.Parse(skipValueOrParameter.Value);
+            }
+
+            InnerCommand.CommandText = InnerCommand.CommandText.Remove(match.Index, match.Length);
+        }
+        
+        protected virtual bool IsParameter(string fragment)
+            => fragment.Equals("?") ||
+               fragment.Length >= 2 && fragment[0] == '@' && fragment[1] != '@';
+        
         protected virtual DbParameter ExtractParameter(string commandText, int count, List<DbParameter> parameters)
         {
             var indices = GetParameterIndices(commandText.Substring(0, count));

src/System.Data.Jet/JetDataReader.cs

@@ -18,6 +18,16 @@ namespace System.Data.Jet
             _wrappedDataReader = dataReader;
         }
         
+        public JetDataReader(DbDataReader dataReader, int skipCount)
+            : this(dataReader)
+        {
+            var i = 0;
+            while (i < skipCount && _wrappedDataReader.Read())
+            {
+                i++;
+            }
+        }
+
         private readonly DbDataReader _wrappedDataReader;
 
         public override void Close()