Marked EnumerableUtils.One as obsolete to not be in use

alex-kulakov · alex-kulakov · commit aa2bbed42d1a · 2026-03-09T15:08:59.000+05:00
There are three dotnet alternatives which work better - Repeat, Append and
Prepend, which cover all the possible scenarios and track actual number of items in
result sequence
diff --git a/Orm/Xtensive.Orm.Tests.Core/Collections/EnumerableExtensionsTest.cs b/Orm/Xtensive.Orm.Tests.Core/Collections/EnumerableExtensionsTest.cs
@@ -112,7 +112,7 @@ private static IEnumerable<Node> Flatten(Node root, bool rootFirst)
 
     private static IEnumerable<Node> Flatten(Node root, bool rootFirst, Action<Node> exitAction)
     {
-      return EnumerableUtils.One(root).Flatten(n => n != null ? n.Children : null, exitAction, rootFirst);
+      return Enumerable.Repeat(root, 1).Flatten(n => n != null ? n.Children : null, exitAction, rootFirst);
     }
 
     [Test]
diff --git a/Orm/Xtensive.Orm.Tests.Core/Collections/TopologicalSorterTest.cs b/Orm/Xtensive.Orm.Tests.Core/Collections/TopologicalSorterTest.cs
@@ -70,7 +70,7 @@ public void SelfReferenceTest()
         {
             var node = new Node<int>(1);
             var edge = new Edge<int>(node, node, 1);
-            var graph = new Graph<Node<int>, Edge<int>>(EnumerableUtils.One(node));
+            var graph = new Graph<Node<int>, Edge<int>>(Enumerable.Repeat(node, 1));
 
             var result = TopologicalSorter.Sort(graph, e => e.Source==e.Target);
             Assert.AreEqual(1, result.SortedNodes.Count);
diff --git a/Orm/Xtensive.Orm.Tests.Core/Helpers/TopologicalSorterTest.cs b/Orm/Xtensive.Orm.Tests.Core/Helpers/TopologicalSorterTest.cs
@@ -126,13 +126,13 @@ public void SelfReferenceTest()
       var connection2 = new NodeConnection<int, string>(node2, node2, "ConnectionItem");
       connection2.BindToNodes();
 
-      var result = TopologicalSorter.SortToList(EnumerableUtils.One(node1), out var removedEdges1);
+      var result = TopologicalSorter.SortToList(Enumerable.Repeat(node1, 1), out var removedEdges1);
       Assert.AreEqual(1, result.Count);
       Assert.AreEqual(node1.Item, result[0]);
       Assert.AreEqual(1, removedEdges1.Count);
       Assert.AreEqual(connection1, removedEdges1[0]);
 
-      result = TopologicalSorter.Sort(EnumerableUtils.One(node2), out var removedEdges2).ToList(1);
+      result = TopologicalSorter.Sort(Enumerable.Repeat(node2, 1), out var removedEdges2).ToList(1);
       Assert.AreEqual(1, result.Count);
       Assert.AreEqual(node2.Item, result[0]);
       Assert.AreEqual(1, removedEdges2.Count);
diff --git a/Orm/Xtensive.Orm.Tests.Sql/MySQL/MiscTests.cs b/Orm/Xtensive.Orm.Tests.Sql/MySQL/MiscTests.cs
@@ -353,7 +353,7 @@ public void FreeTextTest()
     {
       SqlSelect select = SqlDml.Select();
       var table = Catalog.DefaultSchema.Tables["Address"];
-      select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", EnumerableUtils.One(table.Columns[0].Name).ToList(), EnumerableUtils.One(table.Columns[0].Name).ToList()));
+      select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", new[] { table.Columns[0].Name }, new[] { table.Columns[0].Name }));
       select.Columns.Add(select.From.Asterisk);
       Console.WriteLine(SqlDriver.Compile(select).GetCommandText());
     }
diff --git a/Orm/Xtensive.Orm.Tests.Sql/SqlServer/MiscTests.cs b/Orm/Xtensive.Orm.Tests.Sql/SqlServer/MiscTests.cs
@@ -360,7 +360,7 @@ public void FreeTextTest()
     {
       SqlSelect select = SqlDml.Select();
       var table = Catalog.Schemas["Person"].Tables["Address"];
-      select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", EnumerableUtils.One(table.Columns[0].Name).ToList(), EnumerableUtils.One(table.Columns[0].Name).ToList()));
+      select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", new[] { table.Columns[0].Name }, new[] { table.Columns[0].Name }));
       select.Columns.Add(select.From.Asterisk);
       Console.WriteLine(sqlDriver.Compile(select).GetCommandText());
     }
@@ -372,7 +372,7 @@ public void FreeTextTopNByRankTest()
       var table = Catalog.Schemas["Person"].Tables["Address"];
       select.From = SqlDml.QueryRef( SqlDml.FreeTextTable(table,
         "How can I make my own beers",
-        EnumerableUtils.One(table.Columns[0].Name).ToList(),
+        new[] { table.Columns[0].Name },
         (SqlLiteral)5));
       Console.WriteLine(sqlDriver.Compile(select).GetCommandText());
     }
diff --git a/Orm/Xtensive.Orm.Tests/Linq/QueryMethodTests.cs b/Orm/Xtensive.Orm.Tests/Linq/QueryMethodTests.cs
@@ -190,9 +190,9 @@ public async Task Store2AsyncTest()
     private IEnumerable<Customer> GetExpectedCustomerAsSequence()
     {
       if (StorageProviderInfo.Instance.CheckProviderIs(StorageProvider.Firebird)) {
-        return EnumerableUtils.One(Session.Query.All<Customer>().OrderBy(c => c.CustomerId).AsEnumerable().First());
+        return Session.Query.All<Customer>().OrderBy(c => c.CustomerId).AsEnumerable().Take(1);
       }
-      return EnumerableUtils.One(Customers.First());
+      return Enumerable.Repeat(Customers.First(), 1);
     }
   }
 }
diff --git a/Orm/Xtensive.Orm.Tests/Storage/Multinode/QueryCachingTest.cs b/Orm/Xtensive.Orm.Tests/Storage/Multinode/QueryCachingTest.cs
@@ -426,7 +426,7 @@ private int[] GetUnexpectedTypeIds(string nodeId)
       return (nodeId == WellKnown.DefaultNodeId)
         ? CustomUpgradeHandler.TypeIdPerNode.Values.ToArray()
         : CustomUpgradeHandler.TypeIdPerNode.Where(i => i.Key != nodeId)
-            .Select(i => i.Value).Union(EnumerableUtils.One(100)).ToArray();
+            .Select(i => i.Value).Union(Enumerable.Repeat(100, 1)).ToArray();
     }
 
     private List<BaseTestEntity> ExecuteSimpleQueryCaching(Session session) =>
diff --git a/Orm/Xtensive.Orm.Tests/Storage/Prefetch/PrefetchManagerBasicTest.cs b/Orm/Xtensive.Orm.Tests/Storage/Prefetch/PrefetchManagerBasicTest.cs
@@ -951,9 +951,9 @@ private void OpenSessionsAndRunPrefetches()
           var newOrder = new Order();
           var orderDetail = new OrderDetail {Product = new Product()};
           session.SaveChanges();
-          var order = EnumerableUtils.One(newOrder).Prefetch(o => o.Details).First();
+          var order = Enumerable.Repeat(newOrder, 1).Prefetch(o => o.Details).First();
           Assert.That(order, Is.Not.Null);
-          var product = EnumerableUtils.One(orderDetail).Prefetch(d => d.Product).First();
+          var product = Enumerable.Repeat(orderDetail, 1).Prefetch(d => d.Product).First();
           Assert.That(product, Is.Not.Null);
           //Query.All<Order>().Prefetch(o => o.Details).First();
           t.Complete();
diff --git a/Orm/Xtensive.Orm.Tests/Storage/Prefetch/PrefetchTest.cs b/Orm/Xtensive.Orm.Tests/Storage/Prefetch/PrefetchTest.cs
@@ -619,7 +619,7 @@ public void ArgumentsTest()
         AssertEx.Throws<KeyNotFoundException>(() => session.Query.All<Track>()
           .Prefetch(t => t.PersistenceState)
           .ToList());
-        var d = session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(Key.Create<Model.OfferContainer>(Domain, 1)))
+        var d = session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(Key.Create<Model.OfferContainer>(Domain, 1), 1))
           .Prefetch(oc => oc.IntermediateOffer.AnotherContainer.RealOffer.Book)
           .ToList();
       }
@@ -639,7 +639,7 @@ public async Task ArgumentsAsyncTest()
         _ = Assert.ThrowsAsync<KeyNotFoundException>(async () => (await session.Query.All<Track>()
           .Prefetch(t => t.PersistenceState).ExecuteAsync())
           .ToList());
-        var d = (await session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(Key.Create<Model.OfferContainer>(Domain, 1)))
+        var d = (await session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(Key.Create<Model.OfferContainer>(Domain, 1), 1))
           .Prefetch(oc => oc.IntermediateOffer.AnotherContainer.RealOffer.Book).ExecuteAsync())
           .ToList();
       }
@@ -699,7 +699,7 @@ public void RootElementIsNullPrefetchTest()
         }
         using (var tx = session.OpenTransaction()) {
           var books = session.Query.All<Model.Book>().AsEnumerable()
-            .Concat(EnumerableUtils.One<Model.Book>(null)).Prefetch(b => b.Title);
+            .Concat(Enumerable.Repeat<Model.Book>(null, 1)).Prefetch(b => b.Title);
           var titleField = Domain.Model.Types[typeof(Model.Book)].Fields[nameof(Model.Book.Title)];
           var titleType = Domain.Model.Types[typeof(Model.Title)];
           var count = 0;
@@ -727,7 +727,7 @@ public async Task RootElementIsNullPrefetchAsyncTest()
 
         await using (var tx = session.OpenTransaction()) {
           var books = session.Query.All<Model.Book>().AsEnumerable()
-            .Concat(EnumerableUtils.One<Model.Book>(null)).Prefetch(b => b.Title).AsAsyncEnumerable();
+            .Concat(Enumerable.Repeat<Model.Book>(null, 1)).Prefetch(b => b.Title).AsAsyncEnumerable();
           var titleField = Domain.Model.Types[typeof(Model.Book)].Fields[nameof(Model.Book.Title)];
           var titleType = Domain.Model.Types[typeof(Model.Title)];
           var count = 0;
@@ -804,7 +804,7 @@ public void NestedPrefetchWhenRootElementIsNullTest()
           tx.Complete();
         }
         using (var tx = session.OpenTransaction()) {
-          var books = session.Query.All<Model.Book>().AsEnumerable().Concat(EnumerableUtils.One<Model.Book>(null))
+          var books = session.Query.All<Model.Book>().AsEnumerable().Concat(Enumerable.Repeat<Model.Book>(null, 1))
             .Prefetch(b => b.Title.Book);
           var titleField = Domain.Model.Types[typeof (Model.Book)].Fields["Title"];
           var titleType = Domain.Model.Types[typeof (Model.Title)];
@@ -834,7 +834,7 @@ public async Task NestedPrefetchWhenRootElementIsNullAsyncTest()
         }
 
         await using (var tx = session.OpenTransaction()) {
-          var books = session.Query.All<Model.Book>().AsEnumerable().Concat(EnumerableUtils.One<Model.Book>(null))
+          var books = session.Query.All<Model.Book>().AsEnumerable().Concat(Enumerable.Repeat<Model.Book>(null, 1))
             .Prefetch(b => b.Title.Book).AsAsyncEnumerable();
           var titleField = Domain.Model.Types[typeof(Model.Book)].Fields[nameof(Model.Book.Title)];
           var titleType = Domain.Model.Types[typeof(Model.Title)];
@@ -861,7 +861,7 @@ public void StructureFieldsPrefetchTest()
 
       using (var session = Domain.OpenSession())
       using (var tx = session.OpenTransaction()) {
-        var containers = session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(containerKey))
+        var containers = session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(containerKey, 1))
           .Prefetch(oc => oc.RealOffer.Book)
           .Prefetch(oc => oc.IntermediateOffer.RealOffer.BookShop);
         foreach (var key in containers) {
@@ -879,7 +879,7 @@ public async Task StructureFieldsPrefetchAsyncTest()
 
       await using (var session = await Domain.OpenSessionAsync())
       await using (var tx = session.OpenTransaction()) {
-        var containers = session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(containerKey))
+        var containers = session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(containerKey, 1))
           .Prefetch(oc => oc.RealOffer.Book)
           .Prefetch(oc => oc.IntermediateOffer.RealOffer.BookShop).AsAsyncEnumerable();
         await foreach (var key in containers) {
@@ -897,7 +897,7 @@ public void StructurePrefetchTest()
 
       using (var session = Domain.OpenSession())
       using (var tx = session.OpenTransaction()) {
-        var containers = session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(containerKey))
+        var containers = session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(containerKey, 1))
           .Prefetch(oc => oc.IntermediateOffer);
         foreach (var key in containers) {
           PrefetchTestHelper.AssertOnlySpecifiedColumnsAreLoaded(containerKey, containerKey.TypeInfo, session,
@@ -914,7 +914,7 @@ public async Task StructurePrefetchAsyncTest()
 
       await using (var session = await Domain.OpenSessionAsync())
       await using (var tx = session.OpenTransaction()) {
-        var containers = session.Query.Many<Model.OfferContainer>(EnumerableUtils.One(containerKey))
+        var containers = session.Query.Many<Model.OfferContainer>(Enumerable.Repeat(containerKey, 1))
           .Prefetch(oc => oc.IntermediateOffer).AsAsyncEnumerable();
         await foreach (var key in containers) {
           PrefetchTestHelper.AssertOnlySpecifiedColumnsAreLoaded(containerKey, containerKey.TypeInfo, session,
diff --git a/Orm/Xtensive.Orm.Tests/Storage/Randomized/Tree.cs b/Orm/Xtensive.Orm.Tests/Storage/Randomized/Tree.cs
@@ -7,6 +7,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Linq;
 using Xtensive.Collections;
 using Xtensive.Core;
 
@@ -33,7 +34,7 @@ public sealed class Tree : Entity,
     /// <inheritdoc/>
     public IEnumerator<TreeNode> GetEnumerator()
     {
-      return EnumerableUtils.One(Root).Flatten(node => node.Children, null, true).GetEnumerator();
+      return Enumerable.Repeat(Root, 1).Flatten(node => node.Children, null, true).GetEnumerator();
     }
 
     /// <inheritdoc/>
diff --git a/Orm/Xtensive.Orm.Tests/Storage/VersionRootTests.cs b/Orm/Xtensive.Orm.Tests/Storage/VersionRootTests.cs
@@ -60,7 +60,7 @@ public IEnumerable<Entity> GetVersionRoots()
       if (Order==null)
         return Enumerable.Empty<Entity>();
       else 
-        return EnumerableUtils.One((Entity) Order);
+        return Enumerable.Repeat((Entity) Order, 1);
     }
   }
 
diff --git a/Orm/Xtensive.Orm/Collections/EnumerableUtils.cs b/Orm/Xtensive.Orm/Collections/EnumerableUtils.cs
@@ -21,6 +21,7 @@ public static class EnumerableUtils
     /// </summary>
     /// <typeparam name="TItem">The type of enumerated item.</typeparam>
     /// <returns>Sequence with value inside.</returns>
+    [Obsolete("Inefficient compared with Enumerable.Repeat(value, 1), or .Append(value)/.Prepend(value) extensions.")]
     public static IEnumerable<TItem> One<TItem>(TItem value)
     {
       yield return value;
diff --git a/Orm/Xtensive.Orm/Collections/TypeRegistrationProcessorBase.cs b/Orm/Xtensive.Orm/Collections/TypeRegistrationProcessorBase.cs
@@ -34,7 +34,9 @@ public virtual void Process(TypeRegistry registry, TypeRegistration registration
       var types =
         registration.Type==null
           ? FindTypes(registration.Assembly, BaseType, (type, typeFilter) => IsAcceptable(registration, type))
-          : EnumerableUtils.One(registration.Type).Where(t => IsAcceptable(registration, t));
+          : IsAcceptable(registration, registration.Type)
+            ? Enumerable.Repeat(registration.Type, 1)
+            : Enumerable.Empty<Type>();
       foreach (var type in types)
         Process(registry, registration, type);
     }
diff --git a/Orm/Xtensive.Orm/Core/Extensions/EnumerableExtensions.cs b/Orm/Xtensive.Orm/Core/Extensions/EnumerableExtensions.cs
@@ -417,13 +417,13 @@ public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> source, i
       ArgumentValidator.EnsureArgumentIsInRange(maximalBatchSize, 0, int.MaxValue, "maximalBatchSize");
       if(maximalBatchSize < initialBatchSize)
         throw new ArgumentException(String.Format(Strings.ExArgumentXIsLessThanArgumentY,
-          "maximalBatchSize", "initialBatchSize"));
+          nameof(maximalBatchSize), nameof(initialBatchSize)));
       var currentCount = 0;
       var currentBatchSize = initialBatchSize;
       using (var enumerator = source.GetEnumerator()) {
         while (currentCount < firstFastCount && enumerator.MoveNext()) {
           currentCount++;
-          yield return EnumerableUtils.One(enumerator.Current);
+          yield return Enumerable.Repeat(enumerator.Current, 1);
         }
         while (enumerator.MoveNext()) {
           currentCount = 0;
diff --git a/Orm/Xtensive.Orm/Linq/ConstantExtractor.cs b/Orm/Xtensive.Orm/Linq/ConstantExtractor.cs
@@ -49,7 +49,7 @@ public LambdaExpression Process()
       if (constantValues != null)
         throw new InvalidOperationException();
       constantValues = new List<object>();
-      var parameters = EnumerableUtils.One(ConstantParameter).Concat(lambda.Parameters).ToArray(lambda.Parameters.Count + 1);
+      var parameters = lambda.Parameters.Prepend(ConstantParameter).ToArray(lambda.Parameters.Count + 1);
       var body = Visit(lambda.Body);
       // Preserve original delegate type because it may differ from types of parameters / return value
       return FastExpression.Lambda(FixDelegateType(lambda.Type), body, parameters);
diff --git a/Orm/Xtensive.Orm/Orm/Configuration/Internals/ConfigurationSectionExtensions.cs b/Orm/Xtensive.Orm/Orm/Configuration/Internals/ConfigurationSectionExtensions.cs
@@ -26,7 +26,7 @@ public static IEnumerable<IConfigurationSection> GetSelfOrChildren(this IConfigu
         if (isIndexed)
           return children;
         else
-          return EnumerableUtils.One(section);
+          return Enumerable.Repeat(section, 1);
       }
       return children;
     }
diff --git a/Orm/Xtensive.Orm/Orm/Entity.cs b/Orm/Xtensive.Orm/Orm/Entity.cs
@@ -397,12 +397,12 @@ public void Validate()
 
     internal void RemoveLaterInternal(EntityRemoveReason reason)
     {
-      Session.RemovalProcessor.EnqueueForRemoval(EnumerableUtils.One(this), reason);
+      Session.RemovalProcessor.EnqueueForRemoval(Enumerable.Repeat(this, 1), reason);
     }
 
     internal void RemoveInternal(EntityRemoveReason reason)
     {
-      Session.RemovalProcessor.Remove(EnumerableUtils.One(this), reason);
+      Session.RemovalProcessor.Remove(Enumerable.Repeat(this, 1), reason);
     }
 
     /// <exception cref="InvalidOperationException">Entity is removed.</exception>
diff --git a/Orm/Xtensive.Orm/Orm/Internals/Prefetch/Nodes/NodeBuilder.cs b/Orm/Xtensive.Orm/Orm/Internals/Prefetch/Nodes/NodeBuilder.cs
@@ -116,7 +116,7 @@ private IEnumerable<BaseFieldNode> VisitMemberAccess(MemberExpression access)
         result = new FieldNode(path, field);
       }
 
-      return EnumerableUtils.One(result);
+      return Enumerable.Repeat(result, 1);
     }
 
     private static ObjectModel.ReadOnlyCollection<BaseFieldNode> WrapNodes(IEnumerable<BaseFieldNode> nodes)
diff --git a/Orm/Xtensive.Orm/Orm/Linq/Expressions/LocalCollectionExpression.cs b/Orm/Xtensive.Orm/Orm/Linq/Expressions/LocalCollectionExpression.cs
@@ -28,7 +28,7 @@ internal class LocalCollectionExpression : ParameterizedExpression,
     public IEnumerable<ColumnExpression> Columns =>
       Fields
         .SelectMany(field => field.Value is ColumnExpression
-          ? EnumerableUtils.One(field.Value)
+          ? Enumerable.Repeat(field.Value, 1)
           : ((LocalCollectionExpression) field.Value).Columns.Cast<IMappedExpression>())
         .Cast<ColumnExpression>();
 
diff --git a/Orm/Xtensive.Orm/Orm/Linq/ItemToTupleConverter{TItem}.cs b/Orm/Xtensive.Orm/Orm/Linq/ItemToTupleConverter{TItem}.cs
@@ -42,7 +42,7 @@ private class TupleTypeCollection: IReadOnlyCollection<Type>
       public void Add(Type type)
       {
         count++;
-        types = types==null ? EnumerableUtils.One(type) : types.Concat(EnumerableUtils.One(type));
+        types = types==null ? Enumerable.Repeat(type, 1) : types.Append(type);
       }
 
       public void AddRange(IReadOnlyCollection<Type> newTypes)
diff --git a/Orm/Xtensive.Orm/Orm/Operations/KeySetOperation.cs b/Orm/Xtensive.Orm/Orm/Operations/KeySetOperation.cs
@@ -49,7 +49,7 @@ protected override void PrepareSelf(OperationExecutionContext context)
 
     /// <inheritdoc/>
     public KeySetOperation(Key key)
-      : this(EnumerableUtils.One(key))
+      : this(Enumerable.Repeat(key, 1))
     {
     }
 
diff --git a/Orm/Xtensive.Orm/Orm/Rse/Transformation/ColumnMappingInspector.cs b/Orm/Xtensive.Orm/Orm/Rse/Transformation/ColumnMappingInspector.cs
@@ -45,7 +45,7 @@ protected override IncludeProvider VisitInclude(IncludeProvider provider)
 
       var currentMapping = mappings[provider.Source];
       var calulatedColumn = provider.Header.Columns.Last();
-      mappings[provider] = Merge(currentMapping, EnumerableUtils.One(calulatedColumn.Index));
+      mappings[provider] = Merge(currentMapping, Enumerable.Repeat(calulatedColumn.Index, 1));
       if (source == provider.Source) {
         return provider;
       }
@@ -327,7 +327,7 @@ protected override RowNumberProvider VisitRowNumber(RowNumberProvider provider)
       var newSource = VisitCompilable(provider.Source);
       var currentMapping = mappings[provider.Source];
       var rowNumberColumn = provider.Header.Columns.Last();
-      mappings[provider] = Merge(currentMapping, EnumerableUtils.One(rowNumberColumn.Index));
+      mappings[provider] = Merge(currentMapping, Enumerable.Repeat(rowNumberColumn.Index, 1));
       return newSource == provider.Source
         ? provider
         : new RowNumberProvider(newSource, rowNumberColumn.Name);
diff --git a/Orm/Xtensive.Orm/Orm/Transaction.cs b/Orm/Xtensive.Orm/Orm/Transaction.cs
@@ -276,7 +276,7 @@ private void PromoteLifetimeTokens()
     private void PromoteLifetimeTokensToSession()
     {
       if (Outer == null
-          && Session.TryPromoteTokens(EnumerableUtils.One(LifetimeToken).Union(lifetimeTokens))) {
+          && Session.TryPromoteTokens(Enumerable.Repeat(LifetimeToken, 1).Union(lifetimeTokens))) {
         ClearLifetimeTokens();
       }
     }
diff --git a/Orm/Xtensive.Orm/Orm/Upgrade/Internals/HintGenerator.cs b/Orm/Xtensive.Orm/Orm/Upgrade/Internals/HintGenerator.cs
@@ -811,7 +811,7 @@ bool IsMovedToAnotherHierarchy(StoredTypeInfo oldType)
 
     private static IEnumerable<StoredTypeInfo> GetAffectedMappedTypes(StoredTypeInfo type, bool includeInheritors)
     {
-      var result = EnumerableUtils.One(type);
+      var result = Enumerable.Repeat(type, 1);
       if (includeInheritors) {
         result = result.Concat(type.AllDescendants);
       }
@@ -824,7 +824,7 @@ private static IEnumerable<StoredTypeInfo> GetAffectedMappedTypes(StoredTypeInfo
     private static StoredTypeInfo[] GetAffectedMappedTypesAsArray(StoredTypeInfo type, bool includeInheritors)
     {
       var count = 1;
-      var result = EnumerableUtils.One(type);
+      var result = Enumerable.Repeat(type, 1);
       if (includeInheritors) {
         result = result.Concat(type.AllDescendants);
         count += type.AllDescendants.Length;

Original file line number	Diff line number	Diff line change
`@@ -112,7 +112,7 @@ private static IEnumerable<Node> Flatten(Node root, bool rootFirst)`
`112`	`112`
`113`	`113`	`private static IEnumerable<Node> Flatten(Node root, bool rootFirst, Action<Node> exitAction)`
`114`	`114`	`{`
`115`		`- return EnumerableUtils.One(root).Flatten(n => n != null ? n.Children : null, exitAction, rootFirst);`
	`115`	`+ return Enumerable.Repeat(root, 1).Flatten(n => n != null ? n.Children : null, exitAction, rootFirst);`
`116`	`116`	`}`
`117`	`117`
`118`	`118`	`[Test]`
Original file line number	Diff line number	Diff line change
`@@ -70,7 +70,7 @@ public void SelfReferenceTest()`
`70`	`70`	`{`
`71`	`71`	`var node = new Node<int>(1);`
`72`	`72`	`var edge = new Edge<int>(node, node, 1);`
`73`		`- var graph = new Graph<Node<int>, Edge<int>>(EnumerableUtils.One(node));`
	`73`	`+ var graph = new Graph<Node<int>, Edge<int>>(Enumerable.Repeat(node, 1));`
`74`	`74`
`75`	`75`	`var result = TopologicalSorter.Sort(graph, e => e.Source==e.Target);`
`76`	`76`	`Assert.AreEqual(1, result.SortedNodes.Count);`
Original file line number	Diff line number	Diff line change
`@@ -353,7 +353,7 @@ public void FreeTextTest()`
`353`	`353`	`{`
`354`	`354`	`SqlSelect select = SqlDml.Select();`
`355`	`355`	`var table = Catalog.DefaultSchema.Tables["Address"];`
`356`		`- select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", EnumerableUtils.One(table.Columns[0].Name).ToList(), EnumerableUtils.One(table.Columns[0].Name).ToList()));`
	`356`	`+ select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", new[] { table.Columns[0].Name }, new[] { table.Columns[0].Name }));`
`357`	`357`	`select.Columns.Add(select.From.Asterisk);`
`358`	`358`	`Console.WriteLine(SqlDriver.Compile(select).GetCommandText());`
`359`	`359`	`}`
Original file line number	Diff line number	Diff line change
`@@ -360,7 +360,7 @@ public void FreeTextTest()`
`360`	`360`	`{`
`361`	`361`	`SqlSelect select = SqlDml.Select();`
`362`	`362`	`var table = Catalog.Schemas["Person"].Tables["Address"];`
`363`		`- select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", EnumerableUtils.One(table.Columns[0].Name).ToList(), EnumerableUtils.One(table.Columns[0].Name).ToList()));`
	`363`	`+ select.From = SqlDml.QueryRef(SqlDml.FreeTextTable(table, "How can I make my own beers and ales?", new[] { table.Columns[0].Name }, new[] { table.Columns[0].Name }));`
`364`	`364`	`select.Columns.Add(select.From.Asterisk);`
`365`	`365`	`Console.WriteLine(sqlDriver.Compile(select).GetCommandText());`
`366`	`366`	`}`
`@@ -372,7 +372,7 @@ public void FreeTextTopNByRankTest()`
`372`	`372`	`var table = Catalog.Schemas["Person"].Tables["Address"];`
`373`	`373`	`select.From = SqlDml.QueryRef( SqlDml.FreeTextTable(table,`
`374`	`374`	`"How can I make my own beers",`
`375`		`- EnumerableUtils.One(table.Columns[0].Name).ToList(),`
	`375`	`+ new[] { table.Columns[0].Name },`
`376`	`376`	`(SqlLiteral)5));`
`377`	`377`	`Console.WriteLine(sqlDriver.Compile(select).GetCommandText());`
`378`	`378`	`}`
Original file line number	Diff line number	Diff line change
`@@ -190,9 +190,9 @@ public async Task Store2AsyncTest()`
`190`	`190`	`private IEnumerable<Customer> GetExpectedCustomerAsSequence()`
`191`	`191`	`{`
`192`	`192`	`if (StorageProviderInfo.Instance.CheckProviderIs(StorageProvider.Firebird)) {`
`193`		`- return EnumerableUtils.One(Session.Query.All<Customer>().OrderBy(c => c.CustomerId).AsEnumerable().First());`
	`193`	`+ return Session.Query.All<Customer>().OrderBy(c => c.CustomerId).AsEnumerable().Take(1);`
`194`	`194`	`}`
`195`		`- return EnumerableUtils.One(Customers.First());`
	`195`	`+ return Enumerable.Repeat(Customers.First(), 1);`
`196`	`196`	`}`
`197`	`197`	`}`
`198`	`198`	`}`
Original file line number	Diff line number	Diff line change
`@@ -426,7 +426,7 @@ private int[] GetUnexpectedTypeIds(string nodeId)`
`426`	`426`	`return (nodeId == WellKnown.DefaultNodeId)`
`427`	`427`	`? CustomUpgradeHandler.TypeIdPerNode.Values.ToArray()`
`428`	`428`	`: CustomUpgradeHandler.TypeIdPerNode.Where(i => i.Key != nodeId)`
`429`		`- .Select(i => i.Value).Union(EnumerableUtils.One(100)).ToArray();`
	`429`	`+ .Select(i => i.Value).Union(Enumerable.Repeat(100, 1)).ToArray();`
`430`	`430`	`}`
`431`	`431`
`432`	`432`	`private List<BaseTestEntity> ExecuteSimpleQueryCaching(Session session) =>`
Original file line number	Diff line number	Diff line change
`@@ -7,6 +7,7 @@`
`7`	`7`	`using System;`
`8`	`8`	`using System.Collections;`
`9`	`9`	`using System.Collections.Generic;`
	`10`	`+using System.Linq;`
`10`	`11`	`using Xtensive.Collections;`
`11`	`12`	`using Xtensive.Core;`
`12`	`13`
`@@ -33,7 +34,7 @@ public sealed class Tree : Entity,`
`33`	`34`	`/// <inheritdoc/>`
`34`	`35`	`public IEnumerator<TreeNode> GetEnumerator()`
`35`	`36`	`{`
`36`		`- return EnumerableUtils.One(Root).Flatten(node => node.Children, null, true).GetEnumerator();`
	`37`	`+ return Enumerable.Repeat(Root, 1).Flatten(node => node.Children, null, true).GetEnumerator();`
`37`	`38`	`}`
`38`	`39`
`39`	`40`	`/// <inheritdoc/>`