Merge pull request #465 from DataObjects-NET/7.2-prefetchquery-iasyncenumerable

PrefetchQuery<T> implements IAsyncEnumerable<T>

Author: alex-kulakov

ChangeLog/7.2.2-dev.txt

@@ -1,3 +1,5 @@
 [main] Query.CreateDelayedQuery(key, Func<IOrderedQueryable<TElement>>) applies external key instead of default computed, as it suppose to
 [main] QueryEndpoint.SingleAsync()/SingleOrDefaultAsync() get overloads that can recieve one key value as parameter without need to create array explicitly
+[main] PrefetchQuery<T> implements IAsyncEnumerable<T>, extra call for .AsAsyncEmumerable() is not needed for async enumeration
+[main] PrefetchQuery<T>.AsAsyncEmumerable() is marked as Obsolete
 [main] Support for C#14+ optimization that applies ReadOnlySpan<T>.Contains() extension instead of IEnumerable<T>.Contains() one to arrays

Orm/Xtensive.Orm.Manual/Prefetch/PrefetchTest.cs

@@ -180,7 +180,7 @@ public async Task MainAsyncTest()
           .Prefetch(p => p.Photo) // Lazy load field
           .Prefetch(p => p.Employees.Prefetch(e => e.Photo)) // EntitySet Employees and lazy load field of each of its items with the limit on number of items to be loaded
           .Prefetch(p => p.Manager.Photo); // Referenced entity and lazy load field for each of them
-        await foreach (var person in people.AsAsyncEnumerable()) {
+        await foreach (var person in people) {
           var accessor = DirectStateAccessor.Get(person);
           Assert.That(accessor.GetFieldState("Photo"), Is.EqualTo(PersistentFieldState.Loaded));
           Assert.That(accessor.GetFieldState("Manager"), Is.EqualTo(PersistentFieldState.Loaded));
@@ -275,7 +275,7 @@ orderby person.Name
           .Prefetch(p => p.Employees // EntitySet Employees
             .Prefetch(e => e.Photo)) // and lazy load field of each of its items
           .Prefetch(p => p.Manager); // Referenced entity
-        await foreach (var person in prefetchedPeople.AsAsyncEnumerable()) {
+        await foreach (var person in prefetchedPeople) {
           var accessor = DirectStateAccessor.Get(person);
           Assert.That(accessor.GetFieldState("Photo"), Is.EqualTo(PersistentFieldState.Loaded));
           Assert.That(accessor.GetFieldState("Manager"), Is.EqualTo(PersistentFieldState.Loaded));
@@ -362,7 +362,7 @@ public async Task DelayedQueryAsyncTest()
           .Prefetch(p => p.Photo) // Lazy load field
           .Prefetch(p => p.Employees.Prefetch(e => e.Photo)) // EntitySet Employees and lazy load field of each of its items with the limit on number of items to be loaded
           .Prefetch(p => p.Manager.Photo); // Referenced entity and lazy load field for each of them
-        await foreach (var person in people.AsAsyncEnumerable()) {
+        await foreach (var person in people) {
           var accessor = DirectStateAccessor.Get(person);
           Assert.That(accessor.GetFieldState("Photo"), Is.EqualTo(PersistentFieldState.Loaded));
           Assert.That(accessor.GetFieldState("Manager"), Is.EqualTo(PersistentFieldState.Loaded));
@@ -450,7 +450,7 @@ public async Task CachedQueryAsyncTest()
           .Prefetch(p => p.Photo) // Lazy load field
           .Prefetch(p => p.Employees.Prefetch(e => e.Photo)) // EntitySet Employees and lazy load field of each of its items with the limit on number of items to be loaded
           .Prefetch(p => p.Manager.Photo); // Referenced entity and lazy load field for each of them
-        await foreach (var person in people.AsAsyncEnumerable()) {
+        await foreach (var person in people) {
           var accessor = DirectStateAccessor.Get(person);
           Assert.That(accessor.GetFieldState("Photo"), Is.EqualTo(PersistentFieldState.Loaded));
           Assert.That(accessor.GetFieldState("Manager"), Is.EqualTo(PersistentFieldState.Loaded));

Orm/Xtensive.Orm.Tests/Storage/Prefetch/PrefetchTest.cs

@@ -181,8 +181,7 @@ public async Task PrefetchGraphPerformanceAsyncTest()
           .Prefetch(i => i.InvoiceLines
             .Prefetch(id => id.Track)
             .Prefetch(id => id.Track.Album)
-            .Prefetch(id => id.Track.Bytes))
-          .AsAsyncEnumerable();
+            .Prefetch(id => id.Track.Bytes));
         await foreach (var invoice in invoices) {
           var id = invoice.InvoiceId;
           var name = invoice.Customer.CompanyName;
@@ -247,7 +246,7 @@ public async Task EnumerableOfNonEntityAsyncTest()
       await using (var session = await Domain.OpenSessionAsync())
       await using (var tx = session.OpenTransaction()) {
         var invoices = session.Query.Many<Invoice>(keys)
-          .Prefetch(o => o.DesignatedEmployee).AsAsyncEnumerable();
+          .Prefetch(o => o.DesignatedEmployee);
         var invoiceType = Domain.Model.Types[typeof(Invoice)];
         var employeeField = invoiceType.Fields[nameof(Invoice.DesignatedEmployee)];
         var employeeType = Domain.Model.Types[typeof(Employee)];
@@ -361,7 +360,7 @@ public async Task PrefetchManyNotFullBatchAsyncTest()
         var invoicesField = Domain.Model.Types[typeof (Track)].Fields["Playlists"];
         var invoiceLinesField = Domain.Model.Types[typeof (Playlist)].Fields["Tracks"];
         var tracks = session.Query.All<Track>().Take(50)
-          .Prefetch(t => t.Playlists.Prefetch(il => il.Tracks)).AsAsyncEnumerable();
+          .Prefetch(t => t.Playlists.Prefetch(il => il.Tracks));
         int count1 = 0, count2 = 0;
         await foreach (var track in tracks) {
           count1++;
@@ -413,7 +412,7 @@ public async Task PrefetchManySeveralBatchesAsyncTest()
         var trackField = Domain.Model.Types[typeof(InvoiceLine)].Fields[nameof(InvoiceLine.Track)];
         var invoices = session.Query.All<Invoice>()
           .Take(90)
-          .Prefetch(o => o.InvoiceLines.Prefetch(od => od.Track)).AsAsyncEnumerable();
+          .Prefetch(o => o.InvoiceLines.Prefetch(od => od.Track));
         int count1 = 0, count2 = 0;
         await foreach (var invoice in invoices) {
           count1++;
@@ -483,7 +482,7 @@ public async Task PrefetchSingleAsyncTest()
         var employeeType = Domain.Model.Types[typeof(Employee)];
         var invoiceType = Domain.Model.Types[typeof(Invoice)];
         var invoices = session.Query.Many<Invoice>(keys)
-          .Prefetch(o => o.DesignatedEmployee.Invoices).AsAsyncEnumerable();
+          .Prefetch(o => o.DesignatedEmployee.Invoices);
         var count = 0;
         await foreach (var invoice in invoices) {
           Assert.AreEqual(keys[count], invoice.Key);
@@ -674,7 +673,7 @@ public async Task SimultaneouslyUsageOfMultipleEnumeratorsAsyncTest()
       await using (var session = await Domain.OpenSessionAsync())
       await using (var tx = session.OpenTransaction()) {
         var source = session.Query.All<Invoice>().ToList();
-        var prefetchQuery = source.Prefetch(i => i.InvoiceLines).AsAsyncEnumerable();
+        var prefetchQuery = source.Prefetch(i => i.InvoiceLines);
         await using (var enumerator0 = prefetchQuery.GetAsyncEnumerator()) {
           _ = await enumerator0.MoveNextAsync();
           _ = await enumerator0.MoveNextAsync();
@@ -729,7 +728,7 @@ public async Task RootElementIsNullPrefetchAsyncTest()
 
         await using (var tx = session.OpenTransaction()) {
           var books = session.Query.All<PrefetchModel.Book>().AsEnumerable()
-            .Concat(Enumerable.Repeat<PrefetchModel.Book>(null, 1)).Prefetch(b => b.Title).AsAsyncEnumerable();
+            .Concat(Enumerable.Repeat<PrefetchModel.Book>(null, 1)).Prefetch(b => b.Title);
           var titleField = Domain.Model.Types[typeof(PrefetchModel.Book)].Fields[nameof(PrefetchModel.Book.Title)];
           var titleType = Domain.Model.Types[typeof(PrefetchModel.Title)];
           var count = 0;
@@ -783,7 +782,7 @@ public async Task NestedPrefetchWhenChildElementIsNullAsyncTest()
 
         await using (var tx = session.OpenTransaction()) {
           var prefetcher = session.Query.All<PrefetchModel.Book>()
-            .Prefetch(b => b.Title.Book).AsAsyncEnumerable();
+            .Prefetch(b => b.Title.Book);
           var titleField = Domain.Model.Types[typeof(PrefetchModel.Book)].Fields[nameof(PrefetchModel.Book.Title)];
           var titleType = Domain.Model.Types[typeof(PrefetchModel.Title)];
           await foreach (var book in prefetcher) {
@@ -837,7 +836,7 @@ public async Task NestedPrefetchWhenRootElementIsNullAsyncTest()
 
         await using (var tx = session.OpenTransaction()) {
           var books = session.Query.All<PrefetchModel.Book>().AsEnumerable().Concat(Enumerable.Repeat<PrefetchModel.Book>(null, 1))
-            .Prefetch(b => b.Title.Book).AsAsyncEnumerable();
+            .Prefetch(b => b.Title.Book);
           var titleField = Domain.Model.Types[typeof(PrefetchModel.Book)].Fields[nameof(PrefetchModel.Book.Title)];
           var titleType = Domain.Model.Types[typeof(PrefetchModel.Title)];
           var count = 0;
@@ -883,7 +882,7 @@ public async Task StructureFieldsPrefetchAsyncTest()
       await using (var tx = session.OpenTransaction()) {
         var containers = session.Query.Many<PrefetchModel.OfferContainer>(Enumerable.Repeat(containerKey, 1))
           .Prefetch(oc => oc.RealOffer.Book)
-          .Prefetch(oc => oc.IntermediateOffer.RealOffer.BookShop).AsAsyncEnumerable();
+          .Prefetch(oc => oc.IntermediateOffer.RealOffer.BookShop);
         await foreach (var key in containers) {
           PrefetchTestHelper.AssertOnlyDefaultColumnsAreLoaded(book0Key, book0Key.TypeInfo, session);
           PrefetchTestHelper.AssertOnlyDefaultColumnsAreLoaded(bookShop1Key, bookShop1Key.TypeInfo, session);
@@ -917,7 +916,7 @@ public async Task StructurePrefetchAsyncTest()
       await using (var session = await Domain.OpenSessionAsync())
       await using (var tx = session.OpenTransaction()) {
         var containers = session.Query.Many<PrefetchModel.OfferContainer>(Enumerable.Repeat(containerKey, 1))
-          .Prefetch(oc => oc.IntermediateOffer).AsAsyncEnumerable();
+          .Prefetch(oc => oc.IntermediateOffer);
         await foreach (var key in containers) {
           PrefetchTestHelper.AssertOnlySpecifiedColumnsAreLoaded(containerKey, containerKey.TypeInfo, session,
             field => PrefetchTestHelper.IsFieldToBeLoadedByDefault(field) || field.Name.StartsWith("IntermediateOffer"));

Orm/Xtensive.Orm/Orm/PrefetchQuery.cs

@@ -19,8 +19,27 @@ namespace Xtensive.Orm
   /// initial query result.
   /// </summary>
   /// <typeparam name="TElement">The type of the queried elements.</typeparam>
-  public readonly struct PrefetchQuery<TElement> : IEnumerable<TElement>
+  public readonly struct PrefetchQuery<TElement> : IEnumerable<TElement>, IAsyncEnumerable<TElement>
   {
+    #region Nested types
+    private class ExecuteAsyncResult : IEnumerable<TElement>
+    {
+      private readonly List<TElement> items;
+      // We need to hold StrongReferenceContainer to prevent loaded entities from being collected
+      private readonly StrongReferenceContainer referenceContainer;
+
+      IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+      public IEnumerator<TElement> GetEnumerator() => items.GetEnumerator();
+
+      public ExecuteAsyncResult(List<TElement> items, StrongReferenceContainer referenceContainer)
+      {
+        this.items = items;
+        this.referenceContainer = referenceContainer;
+      }
+    }
+    #endregion
+
     private readonly Session session;
     private readonly IEnumerable<TElement> source;
     private readonly SinglyLinkedList<KeyExtractorNode<TElement>> nodes;
@@ -38,38 +57,25 @@ internal PrefetchQuery<TElement> RegisterPath<TValue>(Expression<Func<TElement,
     public IEnumerator<TElement> GetEnumerator() =>
       new PrefetchQueryEnumerable<TElement>(session, source, nodes).GetEnumerator();
 
+    /// <inheritdoc />
+    public IAsyncEnumerator<TElement> GetAsyncEnumerator(CancellationToken token = default) =>
+      new PrefetchQueryAsyncEnumerable<TElement>(session, source, nodes).GetAsyncEnumerator(token);
+
     /// <summary>
     /// Transforms <see cref="PrefetchQuery{TElement}"/> to an <see cref="IAsyncEnumerable{T}"/> sequence.
     /// </summary>
+    [Obsolete("PrefetchQuery itself is an IAsyncEnumerable implementation")]
     public IAsyncEnumerable<TElement> AsAsyncEnumerable() =>
       new PrefetchQueryAsyncEnumerable<TElement>(session, source, nodes);
 
-    private class ExecuteAsyncResult : IEnumerable<TElement>
-    {
-      private readonly List<TElement> items;
-      // We need to hold StrongReferenceContainer to prevent loaded entities from being collected
-      private readonly StrongReferenceContainer referenceContainer;
-
-      IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
-
-      public IEnumerator<TElement> GetEnumerator() => items.GetEnumerator();
-
-      public ExecuteAsyncResult(List<TElement> items, StrongReferenceContainer referenceContainer)
-      {
-        this.items = items;
-        this.referenceContainer = referenceContainer;
-      }
-    }
-
     /// <summary>
     /// Asynchronously executes given <see cref="PrefetchQuery{TElement}"/> instance.
     /// </summary>
     /// <remarks>
     /// <para>
     /// This method internally puts all elements of the resulting sequence to a list
     /// and then it wraps mentioned list as a <see cref="QueryResult{TItem}"/>.
-    /// As a consequence it is more efficient to use asynchronous enumeration over result of
-    /// <see cref="AsAsyncEnumerable"/> method call because it can perform lazily
+    /// As a consequence it is more efficient to use asynchronous enumeration because it can perform lazily
     /// not putting everything into intermediate list.
     /// </para>
     /// <para> Multiple active operations are not supported. Use <see langword="await"/>