CSHARP-3222: Add LINQ support for median and percentile accumulators/window functions

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

@@ -83,6 +83,8 @@ public class Feature
         private static readonly Feature __loookupConciseSyntax = new Feature("LoookupConciseSyntax", WireVersion.Server50);
         private static readonly Feature __loookupDocuments= new Feature("LoookupDocuments", WireVersion.Server60);
         private static readonly Feature __mmapV1StorageEngine = new Feature("MmapV1StorageEngine", WireVersion.Zero, WireVersion.Server42);
+        private static readonly Feature __medianOperator = new Feature("MedianOperator", WireVersion.Server70);
+        private static readonly Feature __percentileOperator = new Feature("PercentileOperator", WireVersion.Server70);
         private static readonly Feature __pickAccumulatorsNewIn52 = new Feature("PickAccumulatorsNewIn52", WireVersion.Server52);
         private static readonly Feature __rankFusionStage = new Feature("RankFusionStage", WireVersion.Server81);
         private static readonly Feature __regexMatch = new Feature("RegexMatch", WireVersion.Server42);
@@ -401,6 +403,16 @@ public class Feature
         [Obsolete("This feature was removed in server version 4.2. As such, this property will be removed in a later release.")]
         public static Feature MmapV1StorageEngine => __mmapV1StorageEngine;
 
+        /// <summary>
+        /// Gets the $median operator added in 7.0
+        /// </summary>
+        public static Feature MedianOperator => __medianOperator;
+
+        /// <summary>
+        /// Gets the $percentile operator added in 7.0
+        /// </summary>
+        public static Feature PercentileOperator => __percentileOperator;
+
         /// <summary>
         /// Gets the pick accumulators new in 5.2 feature.
         /// </summary>

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/AstNodeType.cs

@@ -93,6 +93,9 @@ internal enum AstNodeType
         MatchesEverythingFilter,
         MatchesNothingFilter,
         MatchStage,
+        MedianExpression,
+        MedianAccumulatorExpression,
+        MedianWindowExpression,
         MergeStage,
         ModFilterOperation,
         NaryExpression,
@@ -104,6 +107,9 @@ internal enum AstNodeType
         NullaryWindowExpression,
         OrFilter,
         OutStage,
+        PercentileExpression,
+        PercentileAccumulatorExpression,
+        PercentileWindowExpression,
         PickAccumulatorExpression,
         PickExpression,
         Pipeline,

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs

@@ -597,6 +597,21 @@ public static AstExpression Max(AstExpression arg1, AstExpression arg2)
             return new AstNaryExpression(AstNaryOperator.Max, [arg1, arg2]);
         }
 
+        public static AstExpression Median(AstExpression input)
+        {
+            return new AstMedianExpression(input);
+        }
+
+        public static AstAccumulatorExpression MedianAccumulator(AstExpression input)
+        {
+            return new AstMedianAccumulatorExpression(input);
+        }
+
+        public static AstWindowExpression MedianWindowExpression(AstExpression input, AstWindow window)
+        {
+            return new AstMedianWindowExpression(input, window);
+        }
+
         public static AstExpression Min(AstExpression array)
         {
             return new AstUnaryExpression(AstUnaryOperator.Min, array);
@@ -653,6 +668,21 @@ public static AstExpression Or(params AstExpression[] args)
             return new AstNaryExpression(AstNaryOperator.Or, flattenedArgs);
         }
 
+        public static AstExpression Percentile(AstExpression input, AstExpression percentiles)
+        {
+            return new AstPercentileExpression(input, percentiles);
+        }
+
+        public static AstAccumulatorExpression PercentileAccumulator(AstExpression input, AstExpression percentiles)
+        {
+            return new AstPercentileAccumulatorExpression(input, percentiles);
+        }
+
+        public static AstWindowExpression PercentileWindowExpression(AstExpression input, AstExpression percentiles, AstWindow window)
+        {
+            return new AstPercentileWindowExpression(input, percentiles, window);
+        }
+
         public static AstExpression PickExpression(AstPickOperator @operator, AstExpression source, AstSortFields sortBy, AstVarExpression @as, AstExpression selector, AstExpression n)
         {
             return new AstPickExpression(@operator, source, sortBy, @as, selector, n);

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstMedianAccumulatorExpression.cs

@@ -0,0 +1,63 @@
+/* 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;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Linq.Linq3Implementation.Ast.Visitors;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions
+{
+    internal sealed class AstMedianAccumulatorExpression : AstAccumulatorExpression
+    {
+        private readonly AstExpression _input;
+
+        public AstMedianAccumulatorExpression(AstExpression input)
+        {
+            _input = Ensure.IsNotNull(input, nameof(input));
+        }
+
+        public AstExpression Input => _input;
+
+        public override AstNodeType NodeType => AstNodeType.MedianAccumulatorExpression;
+
+        public override AstNode Accept(AstNodeVisitor visitor)
+        {
+            return visitor.VisitMedianAccumulatorExpression(this);
+        }
+
+        public override BsonValue Render()
+        {
+            return new BsonDocument
+            {
+                {
+                    "$median", new BsonDocument
+                    {
+                        { "input", _input.Render() },
+                        { "method", "approximate" } // server requires this parameter but currently only allows this value
+                    }
+                }
+            };
+        }
+
+        public AstMedianAccumulatorExpression Update(AstExpression input)
+        {
+            if (input == _input)
+            {
+                return this;
+            }
+            return new AstMedianAccumulatorExpression(input);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstMedianExpression.cs

@@ -0,0 +1,63 @@
+/* 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;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Linq.Linq3Implementation.Ast.Visitors;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions
+{
+    internal sealed class AstMedianExpression : AstExpression
+    {
+        private readonly AstExpression _input;
+
+        public AstMedianExpression(AstExpression input)
+        {
+            _input = Ensure.IsNotNull(input, nameof(input));
+        }
+
+        public AstExpression Input => _input;
+
+        public override AstNodeType NodeType => AstNodeType.MedianExpression;
+
+        public override AstNode Accept(AstNodeVisitor visitor)
+        {
+            return visitor.VisitMedianExpression(this);
+        }
+
+        public override BsonValue Render()
+        {
+            return new BsonDocument
+            {
+                {
+                    "$median", new BsonDocument
+                    {
+                        { "input", _input.Render() },
+                        { "method", "approximate" } // server requires this parameter but currently only allows this value
+                    }
+                }
+            };
+        }
+
+        public AstMedianExpression Update(AstExpression input)
+        {
+            if (input == _input)
+            {
+                return this;
+            }
+            return new AstMedianExpression(input);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstMedianWindowExpression.cs

@@ -0,0 +1,69 @@
+/* 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;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Linq.Linq3Implementation.Ast.Visitors;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions
+{
+    internal sealed class AstMedianWindowExpression : AstWindowExpression
+    {
+        private readonly AstExpression _input;
+        private readonly AstWindow _window;
+
+        public AstMedianWindowExpression(AstExpression input, AstWindow window)
+        {
+            _input = Ensure.IsNotNull(input, nameof(input));
+            _window = window;
+        }
+
+        public AstExpression Input => _input;
+
+        public AstWindow Window => _window;
+
+        public override AstNodeType NodeType => AstNodeType.MedianWindowExpression;
+
+        public override AstNode Accept(AstNodeVisitor visitor)
+        {
+            return visitor.VisitMedianWindowExpression(this);
+        }
+
+        public override BsonValue Render()
+        {
+            return new BsonDocument
+            {
+                {
+                    "$median", new BsonDocument
+                    {
+                        { "input", _input.Render() },
+                        { "method", "approximate" } // server requires this parameter but currently only allows this value
+                    }
+                },
+                { "window", _window?.Render(), _window != null }
+            };
+        }
+
+        public AstMedianWindowExpression Update(AstExpression input,  AstWindow window)
+        {
+            if (input == _input && window == _window)
+            {
+                return this;
+            }
+
+            return new AstMedianWindowExpression(input, window);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstPercentileAccumulatorExpression.cs

@@ -0,0 +1,68 @@
+/* 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;
+using MongoDB.Driver.Core.Misc;
+using MongoDB.Driver.Linq.Linq3Implementation.Ast.Visitors;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions
+{
+    internal sealed class AstPercentileAccumulatorExpression : AstAccumulatorExpression
+    {
+        private readonly AstExpression _input;
+        private readonly AstExpression _percentiles;
+
+        public AstPercentileAccumulatorExpression(AstExpression input, AstExpression percentiles)
+        {
+            _input = Ensure.IsNotNull(input, nameof(input));
+            _percentiles = Ensure.IsNotNull(percentiles, nameof(percentiles));
+        }
+
+        public AstExpression Input => _input;
+
+        public AstExpression Percentiles => _percentiles;
+
+        public override AstNodeType NodeType => AstNodeType.PercentileAccumulatorExpression;
+
+        public override AstNode Accept(AstNodeVisitor visitor)
+        {
+            return visitor.VisitPercentileAccumulatorExpression(this);
+        }
+
+        public override BsonValue Render()
+        {
+            return new BsonDocument
+            {
+                {
+                    "$percentile", new BsonDocument
+                    {
+                        { "input", _input.Render() },
+                        { "p", _percentiles.Render() },
+                        { "method", "approximate" } // server requires this parameter but currently only allows this value
+                    }
+                }
+            };
+        }
+
+        public AstPercentileAccumulatorExpression Update(AstExpression input, AstExpression percentiles)
+        {
+            if (input == _input && percentiles == _percentiles)
+            {
+                return this;
+            }
+            return new AstPercentileAccumulatorExpression(input, percentiles);
+        }
+    }
+}