Merge pull request #144 from DataObjects-NET/master-prefetch-graph-issue

Fixes prefetch graph building issue

Author: alex-kulakov

Orm/Xtensive.Orm/Orm/Internals/Prefetch/Nodes/ExpressionMapBuilder.cs

@@ -1,6 +1,6 @@
-// Copyright (C) 2012 Xtensive LLC.
-// All rights reserved.
-// For conditions of distribution and use, see license.
+// Copyright (C) 2012-2021 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
 // Created by: Denis Krjuchkov
 // Created:    2012.02.24
 
@@ -63,7 +63,7 @@ protected override Expression VisitMethodCall(MethodCallExpression call)
         // All lambdas will be associated with single parent.
         call = (MethodCallExpression) source;
         ValidateMethodCall(call);
-        source = call.Arguments[0];
+        source = call.Arguments[0].StripCasts();
         var lambda = call.Arguments[1].StripQuotes();
         subprefetches.Add(lambda);
       }

Orm/Xtensive.Orm/Orm/Internals/Prefetch/PrefetchQueryEnumerable.cs

@@ -1,4 +1,4 @@
-// Copyright (C) 2010-2020 Xtensive LLC.
+// Copyright (C) 2010-2021 Xtensive LLC.
 // This code is distributed under MIT license terms.
 // See the License.txt file in the project root for more information.
 // Created by: Alexis Kochetov
@@ -125,13 +125,6 @@ private StrongReferenceContainer ProcessFetchedElements(Guid enumerationId)
       return container;
     }
 
-    //private void Initialize()
-    //{
-    //  unknownTypeQueue = new Queue<Key>();
-    //  prefetchQueue = new Queue<Pair<IEnumerable<Key>, IHasNestedNodes>>();
-    //  fieldDescriptorCache = new Dictionary<Pair<IHasNestedNodes, TypeInfo>, IList<PrefetchFieldDescriptor>>();
-    //}
-
     public PrefetchQueryEnumerable(Session session, IEnumerable<TItem> source,
       SinglyLinkedList<KeyExtractorNode<TItem>> nodes)
     {

Orm/Xtensive.Orm/Orm/PrefetchExtensions.cs

@@ -92,6 +92,21 @@ 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 sequence.</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 PrefetchQuery<TElement> source,
+      Expression<Func<TElement, TFieldValue>> expression)
+    {
+      return source.RegisterPath(expression);
+    }
+
     /// <summary>
     /// Creates <see cref="PrefetchQuery{T}"/> for the specified <paramref name="source"/> and
     /// registers the prefetch of the field specified by <paramref name="expression"/>.