address pr comments

Author: adelinowona

src/MongoDB.Driver/SortDefinition.cs

@@ -47,6 +47,9 @@ public abstract class SortDefinition<TDocument>
         /// <returns>A <see cref="BsonDocument"/>.</returns>
         public abstract BsonDocument Render(RenderArgs<TDocument> args);
 
+        // TODO: remove this and refactor Render to return a BsonValue in 4.0
+        internal virtual BsonValue RenderAsBsonValue(RenderArgs<TDocument> args) => Render(args);
+
         /// <summary>
         /// Performs an implicit conversion from <see cref="BsonDocument"/> to <see cref="SortDefinition{TDocument}"/>.
         /// </summary>

src/MongoDB.Driver/SortDefinitionBuilder.cs

@@ -133,10 +133,10 @@ public sealed class SortDefinitionBuilder<TDocument>
         /// <summary>
         /// Creates a value ascending sort.
         /// </summary>
-        /// <returns>An ascending sort.</returns>
+        /// <returns>A value ascending sort.</returns>
         public SortDefinition<TDocument> Ascending()
         {
-            return new NoFieldDirectionalSortDefinition<TDocument>(SortDirection.Ascending);
+            return new ValueDirectionalSortDefinition<TDocument>(SortDirection.Ascending);
         }
 
         /// <summary>
@@ -182,10 +182,10 @@ public SortDefinition<TDocument> Combine(IEnumerable<SortDefinition<TDocument>>
         /// <summary>
         /// Creates a value descending sort.
         /// </summary>
-        /// <returns>A descending sort.</returns>
+        /// <returns>A value descending sort.</returns>
         public SortDefinition<TDocument> Descending()
         {
-            return new NoFieldDirectionalSortDefinition<TDocument>(SortDirection.Descending);
+            return new ValueDirectionalSortDefinition<TDocument>(SortDirection.Descending);
         }
 
         /// <summary>
@@ -251,7 +251,7 @@ public CombinedSortDefinition(IEnumerable<SortDefinition<TDocument>> sorts)
         {
             _sorts = Ensure.IsNotNull(sorts, nameof(sorts)).ToList();
 
-            if (_sorts.Any(sort => sort is NoFieldDirectionalSortDefinition<TDocument>))
+            if (_sorts.Any(sort => sort is ValueDirectionalSortDefinition<TDocument>))
             {
                 throw new InvalidOperationException("Value-based sort cannot be combined with other sorts. When sorting by the entire element value, no other sorting criteria can be applied.");
             }
@@ -295,42 +295,25 @@ public override BsonDocument Render(RenderArgs<TDocument> args)
         {
             var renderedField = _field.Render(args);
 
-            BsonValue value;
-            switch (_direction)
-            {
-                case SortDirection.Ascending:
-                    value = 1;
-                    break;
-                case SortDirection.Descending:
-                    value = -1;
-                    break;
-                default:
-                    throw new InvalidOperationException("Unknown value for " + typeof(SortDirection) + ".");
-            }
-
-            return new BsonDocument(renderedField.FieldName, value);
+            return new BsonDocument(renderedField.FieldName, _direction.ToBsonValue());
         }
     }
 
-    internal sealed class NoFieldDirectionalSortDefinition<TDocument> : SortDefinition<TDocument>
+    internal sealed class ValueDirectionalSortDefinition<TDocument> : SortDefinition<TDocument>
     {
         private readonly SortDirection _direction;
 
-        public NoFieldDirectionalSortDefinition(SortDirection direction)
+        public ValueDirectionalSortDefinition(SortDirection direction)
         {
             _direction = direction;
         }
 
+        internal override BsonValue RenderAsBsonValue(RenderArgs<TDocument> args) => _direction.ToBsonValue();
+
         public override BsonDocument Render(RenderArgs<TDocument> args)
         {
-            BsonValue value = _direction switch
-            {
-                SortDirection.Ascending => 1,
-                SortDirection.Descending => -1,
-                _ => throw new InvalidOperationException("Unknown value for " + typeof(SortDirection) + ".")
-            };
-
-            return new BsonDocument("direction",  value);
+            throw new InvalidOperationException(
+                "Value-based sort cannot be rendered as a document. You might be trying to use a value-based sort where a field-based sort is expected.");
         }
     }
 }

src/MongoDB.Driver/SortDirectionExtensions.cs

@@ -0,0 +1,33 @@
+/* Copyright 2010-present MongoDB Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System;
+using MongoDB.Bson;
+
+namespace MongoDB.Driver
+{
+    internal static class SortDirectionExtensions
+    {
+        internal static BsonValue ToBsonValue(this SortDirection direction)
+        {
+            return direction switch
+            {
+                SortDirection.Ascending => 1,
+                SortDirection.Descending => -1,
+                _ => throw new InvalidOperationException($"Invalid sort direction: {direction}.")
+            };
+        }
+    }
+}

src/MongoDB.Driver/UpdateDefinitionBuilder.cs

@@ -1685,13 +1685,7 @@ public override BsonValue Render(RenderArgs<TDocument> args)
 
             if (_sort != null)
             {
-                var newArgs = args.WithNewDocumentType((IBsonSerializer<TItem>)itemSerializer);
-
-                var renderedSort = _sort is NoFieldDirectionalSortDefinition<TItem>
-                    ? _sort.Render(newArgs)["direction"]
-                    : _sort.Render(newArgs);
-
-                document["$push"][renderedField.FieldName]["$sort"] = renderedSort;
+                document["$push"][renderedField.FieldName]["$sort"] = _sort.RenderAsBsonValue(args.WithNewDocumentType((IBsonSerializer<TItem>)itemSerializer));
             }
 
             return document;

tests/MongoDB.Driver.Tests/SortDefinitionBuilderTests.cs

@@ -33,7 +33,7 @@ public void Ascending()
         }
 
         [Fact]
-        public void Ascending_no_field()
+        public void Ascending_value()
         {
             var subject = CreateSubject<BsonDocument>();
 
@@ -104,7 +104,7 @@ public void Descending()
         }
 
         [Fact]
-        public void Descending_no_field()
+        public void Descending_value()
         {
             var subject = CreateSubject<BsonDocument>();