CSHARP-5672: Support sorting by value in PushEach operation

src/MongoDB.Driver/SortDefinitionBuilder.cs

@@ -130,6 +130,15 @@ public static SortDefinition<TDocument> MetaTextScore<TDocument>(this SortDefini
     /// <typeparam name="TDocument">The type of the document.</typeparam>
     public sealed class SortDefinitionBuilder<TDocument>
     {
+        /// <summary>
+        /// Creates a value ascending sort.
+        /// </summary>
+        /// <returns>An ascending sort.</returns>
+        public SortDefinition<TDocument> Ascending()
+        {
+            return new NoFieldDirectionalSortDefinition<TDocument>(SortDirection.Ascending);
+        }
+
         /// <summary>
         /// Creates an ascending sort.
         /// </summary>
@@ -170,6 +179,15 @@ public SortDefinition<TDocument> Combine(IEnumerable<SortDefinition<TDocument>>
             return new CombinedSortDefinition<TDocument>(sorts);
         }
 
+        /// <summary>
+        /// Creates a value descending sort.
+        /// </summary>
+        /// <returns>A descending sort.</returns>
+        public SortDefinition<TDocument> Descending()
+        {
+            return new NoFieldDirectionalSortDefinition<TDocument>(SortDirection.Descending);
+        }
+
         /// <summary>
         /// Creates a descending sort.
         /// </summary>
@@ -232,6 +250,11 @@ internal sealed class CombinedSortDefinition<TDocument> : SortDefinition<TDocume
         public CombinedSortDefinition(IEnumerable<SortDefinition<TDocument>> sorts)
         {
             _sorts = Ensure.IsNotNull(sorts, nameof(sorts)).ToList();
+
+            if (_sorts.Any(sort => sort is NoFieldDirectionalSortDefinition<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.");
+            }
         }
 
         public override BsonDocument Render(RenderArgs<TDocument> args)
@@ -288,4 +311,26 @@ public override BsonDocument Render(RenderArgs<TDocument> args)
             return new BsonDocument(renderedField.FieldName, value);
         }
     }
+
+    internal sealed class NoFieldDirectionalSortDefinition<TDocument> : SortDefinition<TDocument>
+    {
+        private readonly SortDirection _direction;
+
+        public NoFieldDirectionalSortDefinition(SortDirection direction)
+        {
+            _direction = direction;
+        }
+
+        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);
+        }
+    }
 }

src/MongoDB.Driver/UpdateDefinitionBuilder.cs

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

tests/MongoDB.Driver.Tests/SortDefinitionBuilderTests.cs

@@ -13,6 +13,7 @@
 * limitations under the License.
 */
 
+using System;
 using FluentAssertions;
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization;
@@ -31,6 +32,14 @@ public void Ascending()
             Assert(subject.Ascending("a"), "{a: 1}");
         }
 
+        [Fact]
+        public void Ascending_no_field()
+        {
+            var subject = CreateSubject<BsonDocument>();
+
+            Assert(subject.Ascending(), "{direction: 1}");
+        }
+
         [Fact]
         public void Ascending_Typed()
         {
@@ -76,6 +85,16 @@ public void Combine_with_repeated_fields_using_extension_methods()
             Assert(sort, "{b: -1, a: -1}");
         }
 
+        [Fact]
+        public void Combine_with_value_based_sort_and_additional_sort_should_throw()
+        {
+            var subject = CreateSubject<BsonDocument>();
+
+            var exception = Record.Exception(() => subject.Ascending().Descending("b"));
+
+            exception.Should().BeOfType<InvalidOperationException>();
+        }
+
         [Fact]
         public void Descending()
         {
@@ -84,6 +103,14 @@ public void Descending()
             Assert(subject.Descending("a"), "{a: -1}");
         }
 
+        [Fact]
+        public void Descending_no_field()
+        {
+            var subject = CreateSubject<BsonDocument>();
+
+            Assert(subject.Descending(), "{direction: -1}");
+        }
+
         [Fact]
         public void Descending_Typed()
         {