Merge pull request #123 from DataObjects-NET/prefetch-for-delayedquery

Dedicated Prefetch extensions for DelayedQuery{T} and QueryResult{T}

Author: alex-kulakov

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

@@ -1,4 +1,4 @@
-// Copyright (C) 2008-2020 Xtensive LLC.
+// Copyright (C) 2008-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 // Created by: Alex Yakunin
@@ -14,7 +14,7 @@
 using System.Threading.Tasks;
 using Xtensive.Collections;
 using Xtensive.Collections.Graphs;
-using Xtensive.Orm.Internals;
+using Xtensive.Orm;
 
 
 namespace Xtensive.Core

Orm/Xtensive.Orm/Core/Extensions/EnumerableExtensions.cs

@@ -1,4 +1,4 @@
-// Copyright (C) 2009-2020 Xtensive LLC.
+// Copyright (C) 2009-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 // Created by: Alexander Nikolaev
@@ -10,9 +10,10 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Xtensive.Core;
+using Xtensive.Orm.Internals;
 using Xtensive.Orm.Linq;
 
-namespace Xtensive.Orm.Internals
+namespace Xtensive.Orm
 {
   /// <summary>
   /// Represents a delayed sequence query (query where result can be enumerated after an execution).

Orm/Xtensive.Orm/Orm/DelayedQuery{T}.cs

@@ -1,4 +1,4 @@
-// Copyright (C) 2020 Xtensive LLC.
+// Copyright (C) 2020-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 
@@ -11,20 +11,23 @@
 
 namespace Xtensive.Orm.Linq.Materialization
 {
-  public interface IMaterializingReader<out TItem>
+  internal interface IMaterializingReader<out TItem>
   {
+    Session Session { get; }
     IEnumerator<TItem> AsEnumerator();
     IAsyncEnumerator<TItem> AsAsyncEnumerator();
   }
 
-  public class MaterializingReader<TItem>: IMaterializingReader<TItem>, IEnumerator<TItem>, IAsyncEnumerator<TItem>
+  internal class MaterializingReader<TItem>: IMaterializingReader<TItem>, IEnumerator<TItem>, IAsyncEnumerator<TItem>
   {
     private readonly RecordSetReader recordSetReader;
     private readonly MaterializationContext context;
     private readonly ParameterContext parameterContext;
     private readonly IItemMaterializer<TItem> itemMaterializer;
     private readonly Queue<Action> materializationQueue;
 
+    public Session Session => context.Session;
+
     public IEnumerator<TItem> AsEnumerator()
     {
       recordSetReader.Reset();

Orm/Xtensive.Orm/Orm/Linq/Materialization/MaterializingReader.cs

@@ -1,4 +1,4 @@
-// Copyright (C) 2009-2020 Xtensive LLC.
+// Copyright (C) 2009-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 // Created by: Alexander Nikolaev
@@ -37,6 +37,42 @@ public static PrefetchQuery<TElement> Prefetch<TElement, TFieldValue>(
       return Prefetch(source, Session.Demand(), expression);
     }
 
+    /// <summary>
+    /// Registers fields specified by <paramref name="expression"/> for prefetch.
+    /// </summary>
+    /// <typeparam name="TElement">The type of the element of the source sequence.</typeparam>
+    /// <typeparam name="TFieldValue">The type of the field's value to be prefetched.</typeparam>
+    /// <param name="source">The source query.</param>
+    /// <param name="expression">The expression specifying a field to be prefetched.</param>
+    /// <returns>An <see cref="IEnumerable{TElement}"/> of source items.</returns>
+    public static PrefetchQuery<TElement> Prefetch<TElement, TFieldValue>(
+      this DelayedQuery<TElement> source,
+      Expression<Func<TElement, TFieldValue>> expression)
+    {
+      return new PrefetchQuery<TElement>(source.Session, source).RegisterPath(expression);
+    }
+
+    /// <summary>
+    /// Registers fields specified by <paramref name="expression"/> for prefetch.
+    /// </summary>
+    /// <typeparam name="TElement">The type of the element of the source sequence.</typeparam>
+    /// <typeparam name="TFieldValue">The type of the field's value to be prefetched.</typeparam>
+    /// <param name="source">The source query.</param>
+    /// <param name="expression">The expression specifying a field to be prefetched.</param>
+    /// <returns>An <see cref="IEnumerable{TElement}"/> of source items.</returns>
+    public static PrefetchQuery<TElement> Prefetch<TElement, TFieldValue>(
+      this QueryResult<TElement> source,
+      Expression<Func<TElement, TFieldValue>> expression)
+    {
+      var session = source.Session;
+      if (session != null) {
+        return new PrefetchQuery<TElement>(session, source).RegisterPath(expression);
+      }
+      return new PrefetchQuery<TElement>(Session.Demand(), source).RegisterPath(expression);
+    }
+
+
+
     /// <summary>
     /// Registers fields specified by <paramref name="expression"/> for prefetch.
     /// </summary>

Orm/Xtensive.Orm/Orm/PrefetchExtensions.cs

@@ -1,10 +1,11 @@
-// Copyright (C) 2020 Xtensive LLC.
+// Copyright (C) 2020-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using JetBrains.Annotations;
 using Xtensive.Orm.Linq.Materialization;
 
 namespace Xtensive.Orm
@@ -19,6 +20,8 @@ private class EnumerableReader : IMaterializingReader<TItem>
     {
       private readonly IEnumerable<TItem> items;
 
+      public Session Session => null;
+
       public IEnumerator<TItem> AsEnumerator() => items.GetEnumerator();
 
       public IAsyncEnumerator<TItem> AsAsyncEnumerator() => throw new System.NotSupportedException();
@@ -29,8 +32,11 @@ public EnumerableReader(IEnumerable<TItem> items)
       }
     }
 
-    private readonly IMaterializingReader<TItem> reader;
     private readonly StateLifetimeToken lifetimeToken;
+    private readonly IMaterializingReader<TItem> reader;
+
+    [CanBeNull]
+    internal Session Session => reader.Session;
 
     /// <inheritdoc/>
     IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
@@ -70,7 +76,7 @@ internal QueryResult(IMaterializingReader<TItem> reader, StateLifetimeToken life
     internal QueryResult(IEnumerable<TItem> items)
     {
       reader = new EnumerableReader(items);
-      this.lifetimeToken = default;
+      lifetimeToken = default;
     }
   }
 }