CSHARP-5505: Add $geoNear stage aggregation builders

src/MongoDB.Driver/Core/Misc/Feature.cs

@@ -311,6 +311,8 @@ public class Feature
         /// <summary>
         /// Gets the geoNear command feature.
         /// </summary>
+        ///
+        [Obsolete("This property will be removed in a later release.")]
         public static Feature GeoNearCommand => __geoNearCommand;
 
         /// <summary>

src/MongoDB.Driver/GeoNearOptions.cs

@@ -0,0 +1,71 @@
+/* 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 MongoDB.Bson.Serialization;
+
+namespace MongoDB.Driver
+{
+    /// <summary>
+    /// Represents options for the $geoNear stage.
+    /// </summary>
+    public class GeoNearOptions<TInputDocument, TOutputDocument>
+    {
+        /// <summary>
+        /// Gets or sets the output field that contains the calculated distance. Required if querying a time-series collection.
+        /// Optional for non-time series collections in MongoDB 8.1+
+        /// </summary>
+        public FieldDefinition<TOutputDocument> DistanceField { get; set; }
+
+        /// <summary>
+        /// Gets or sets the factor to multiply all distances returned by the query.
+        /// </summary>
+        public double? DistanceMultiplier { get; set; }
+
+        /// <summary>
+        /// Gets or sets the output field that identifies the location used to calculate the distance.
+        /// </summary>
+        public FieldDefinition<TOutputDocument> IncludeLocs { get; set; }
+
+        /// <summary>
+        /// Gets or sets the geospatial indexed field used when calculating the distance.
+        /// </summary>
+        public string Key { get; set; }
+
+        /// <summary>
+        /// Gets or sets the max distance from the center point that the documents can be.
+        /// </summary>
+        public double? MaxDistance { get; set; }
+
+        /// <summary>
+        /// Gets or sets the min distance from the center point that the documents can be.
+        /// </summary>
+        public double? MinDistance { get; set; }
+
+        /// <summary>
+        /// Gets or sets the output serializer.
+        /// </summary>
+        public IBsonSerializer<TOutputDocument> OutputSerializer { get; set; }
+
+        /// <summary>
+        /// Gets or sets the query that limits the results to the documents that match the query.
+        /// </summary>
+        public FilterDefinition<TInputDocument> Query { get; set; }
+
+        /// <summary>
+        /// Gets or sets the spherical option which determines how to calculate the distance between two points.
+        /// </summary>
+        public bool? Spherical { get; set; }
+    }
+}

src/MongoDB.Driver/IAggregateFluentExtensions.cs

@@ -22,6 +22,7 @@
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization;
 using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.GeoJsonObjectModel;
 
 namespace MongoDB.Driver
 {
@@ -252,6 +253,44 @@ public static IAggregateFluent<TNewResult> Facet<TResult, TNewResult>(
             return aggregate.AppendStage(PipelineStageDefinitionBuilder.Facet<TResult, TNewResult>(facets));
         }
 
+        /// <summary>
+        /// Appends a $geoNear stage to the pipeline.
+        /// </summary>
+        /// <typeparam name="TResult">The type of the result.</typeparam>
+        /// <typeparam name="TNewResult">The type of the new result.</typeparam>
+        /// <typeparam name="TCoordinates">The type of the coordinates for the point.</typeparam>
+        /// <param name="aggregate">The aggregate.</param>
+        /// <param name="near">The point for which to find the closest documents.</param>
+        /// <param name="options">The options.</param>
+        /// <returns>The fluent aggregate interface.</returns>
+        public static IAggregateFluent<TNewResult> GeoNear<TResult, TCoordinates, TNewResult>(
+            this IAggregateFluent<TResult> aggregate,
+            GeoJsonPoint<TCoordinates> near,
+            GeoNearOptions<TResult, TNewResult> options = null)
+            where TCoordinates : GeoJsonCoordinates
+        {
+            Ensure.IsNotNull(aggregate, nameof(aggregate));
+            return aggregate.AppendStage(PipelineStageDefinitionBuilder.GeoNear<TResult, GeoJsonPoint<TCoordinates>, TNewResult>(near, options));
+        }
+
+        /// <summary>
+        /// Appends a $geoNear stage to the pipeline.
+        /// </summary>
+        /// <typeparam name="TResult">The type of the result.</typeparam>
+        /// <typeparam name="TNewResult">The type of the new result.</typeparam>
+        /// <param name="aggregate">The aggregate.</param>
+        /// <param name="near">The point for which to find the closest documents.</param>
+        /// <param name="options">The options.</param>
+        /// <returns>The fluent aggregate interface.</returns>
+        public static IAggregateFluent<TNewResult> GeoNear<TResult, TNewResult>(
+            this IAggregateFluent<TResult> aggregate,
+            double[] near,
+            GeoNearOptions<TResult, TNewResult> options = null)
+        {
+            Ensure.IsNotNull(aggregate, nameof(aggregate));
+            return aggregate.AppendStage(PipelineStageDefinitionBuilder.GeoNear<TResult, TNewResult>(near, options));
+        }
+
         /// <summary>
         /// Appends a $graphLookup stage to the pipeline.
         /// </summary>

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Stages/AstGeoNearStage.cs

@@ -45,7 +45,7 @@ public AstGeoNearStage(
             string key)
         {
             _near = Ensure.IsNotNull(near, nameof(near));
-            _distanceField = Ensure.IsNotNull(distanceField, nameof(distanceField));
+            _distanceField = distanceField;
             _spherical = spherical;
             _maxDistance = maxDistance;
             _query = query;
@@ -80,7 +80,7 @@ public override BsonValue Render()
                 { "$geoNear", new BsonDocument
                     {
                         { "near", _near },
-                        { "distanceField", _distanceField },
+                        { "distanceField", _distanceField, _distanceField != null },
                         { "spherical", () => _spherical.Value, _spherical.HasValue },
                         { "maxDistance", () => _maxDistance.Value, _maxDistance.HasValue },
                         { "query", _query, _query != null },

src/MongoDB.Driver/PipelineDefinitionBuilder.cs

@@ -20,6 +20,7 @@
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization;
 using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.GeoJsonObjectModel;
 using MongoDB.Driver.Search;
 
 namespace MongoDB.Driver
@@ -484,6 +485,46 @@ public static PipelineDefinition<TInput, TInput> For<TInput>(IBsonSerializer<TIn
             return new EmptyPipelineDefinition<TInput>(inputSerializer);
         }
 
+        /// <summary>
+        /// Appends a $geoNear stage to the pipeline.
+        /// </summary>
+        /// <typeparam name="TInput">The type of the input documents.</typeparam>
+        /// <typeparam name="TIntermediate">The type of the intermediate documents.</typeparam>
+        /// <typeparam name="TOutput">The type of the output documents.</typeparam>
+        /// <typeparam name="TCoordinates">The type of the coordinates for the point.</typeparam>
+        /// <param name="pipeline">The pipeline.</param>
+        /// <param name="near">The point for which to find the closest documents.</param>
+        /// <param name="options">The options.</param>
+        /// <returns>A new pipeline with an additional stage.</returns>
+        public static PipelineDefinition<TInput, TOutput> GeoNear<TInput, TIntermediate, TCoordinates, TOutput>(
+            this PipelineDefinition<TInput, TIntermediate> pipeline,
+            GeoJsonPoint<TCoordinates> near,
+            GeoNearOptions<TIntermediate, TOutput> options = null)
+            where TCoordinates : GeoJsonCoordinates
+        {
+            Ensure.IsNotNull(pipeline, nameof(pipeline));
+            return pipeline.AppendStage(PipelineStageDefinitionBuilder.GeoNear(near, options));
+        }
+
+        /// <summary>
+        /// Appends a $geoNear stage to the pipeline.
+        /// </summary>
+        /// <typeparam name="TInput">The type of the input documents.</typeparam>
+        /// <typeparam name="TIntermediate">The type of the intermediate documents.</typeparam>
+        /// <typeparam name="TOutput">The type of the output documents.</typeparam>
+        /// <param name="pipeline">The pipeline.</param>
+        /// <param name="near">The point for which to find the closest documents.</param>
+        /// <param name="options">The options.</param>
+        /// <returns>A new pipeline with an additional stage.</returns>
+        public static PipelineDefinition<TInput, TOutput> GeoNear<TInput, TIntermediate, TOutput>(
+            this PipelineDefinition<TInput, TIntermediate> pipeline,
+            double[] near,
+            GeoNearOptions<TIntermediate, TOutput> options = null)
+        {
+            Ensure.IsNotNull(pipeline, nameof(pipeline));
+            return pipeline.AppendStage(PipelineStageDefinitionBuilder.GeoNear(near, options));
+        }
+
         /// <summary>
         /// Appends a $graphLookup stage to the pipeline.
         /// </summary>