CSHARP-956: Aggregate command with $out cannot be sent to secondary.

Author: rstam

MongoDB.Driver/CanCommandBeSentToSecondary.cs

@@ -16,6 +16,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Linq;
 using MongoDB.Bson;
 using MongoDB.Driver.Internal;
 
@@ -30,7 +31,6 @@ public static class CanCommandBeSentToSecondary
         private static Func<BsonDocument, bool> __delegate = DefaultImplementation;
         private static HashSet<string> __secondaryOkCommands = new HashSet<string>(StringComparer.InvariantCultureIgnoreCase)
         {
-            "aggregate",
             "collStats",
             "dbStats",
             "count",
@@ -80,6 +80,17 @@ public static bool DefaultImplementation(BsonDocument document)
                 return true;
             }
 
+            if (commandName.Equals("aggregate", StringComparison.InvariantCultureIgnoreCase))
+            {
+                var pipeline = document["pipeline"].AsBsonArray;
+                if (pipeline.Any(s => s.AsBsonDocument.GetElement(0).Name == "$out"))
+                {
+                    return false;
+                }
+
+                return true;
+            }
+
             if (commandName.Equals("mapreduce", StringComparison.InvariantCultureIgnoreCase))
             {
                 BsonValue outValue;

MongoDB.DriverUnitTests/CanCommandBeSentToSecondaryTests.cs

@@ -16,6 +16,7 @@
 using System;
 using MongoDB.Bson;
 using MongoDB.Driver;
+using MongoDB.Driver.Builders;
 using NUnit.Framework;
 
 namespace MongoDB.DriverUnitTests
@@ -39,7 +40,22 @@ public void TestSetDelegate()
             CanCommandBeSentToSecondary.Delegate = CanCommandBeSentToSecondary.DefaultImplementation; // reset Delegate
         }
 
-        [TestCase("aggregate", true)]
+        [Test]
+        public void TestCanSendAggregateWithReadOnlyPipelineToSecondary()
+        {
+            var pipeline = new BsonArray
+            {
+                new BsonDocument { { "$match", new BsonDocument("x", 1) } }
+            };
+            var command = new BsonDocument
+            {
+                { "aggregate", "collection" },
+                { "pipeline", pipeline }
+            };
+            var result = CanCommandBeSentToSecondary.DefaultImplementation(command);
+            Assert.IsTrue(result);
+        }
+
         [TestCase("collStats", true)]
         [TestCase("dbStats", true)]
         [TestCase("count", true)]
@@ -76,6 +92,23 @@ public void TestCanSendInlineMapReduceToSecondary()
             Assert.IsTrue(result);
         }
 
+        [Test]
+        public void TestCannotSendAggregateWithWritePipelineToSecondary()
+        {
+            var pipeline = new BsonArray
+            {
+                new BsonDocument { { "$match", new BsonDocument("x", 1) } },
+                new BsonDocument { { "$out", "output" } }
+            };
+            var command = new BsonDocument
+            {
+                { "aggregate", "collection" },
+                { "pipeline", pipeline }
+            };
+            var result = CanCommandBeSentToSecondary.DefaultImplementation(command);
+            Assert.IsFalse(result);
+        }
+
         [Test]
         public void TestCannotSendNonInlineMapReduceToSecondary()
         {