CSHARP-2221: RunCommand should use transaction's ReadPreference.

Author: rstam

src/MongoDB.Driver/MongoCollectionImpl.cs

@@ -27,7 +27,6 @@
 using MongoDB.Driver.Core.Operations;
 using MongoDB.Driver.Core.WireProtocol.Messages.Encoders;
 using MongoDB.Driver.Linq;
-using MongoDB.Bson.Serialization.Serializers;
 
 namespace MongoDB.Driver
 {
@@ -977,8 +976,8 @@ private IBsonSerializer<TField> GetValueSerializerForDistinct<TField>(RenderedFi
 
         private TResult ExecuteReadOperation<TResult>(IClientSessionHandle session, IReadOperation<TResult> operation, CancellationToken cancellationToken = default(CancellationToken))
         {
-            var readPreference = GetReadPreference(session);
-            return ExecuteReadOperation(session, operation, readPreference, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, null, _settings.ReadPreference);
+            return ExecuteReadOperation(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         private TResult ExecuteReadOperation<TResult>(IClientSessionHandle session, IReadOperation<TResult> operation, ReadPreference readPreference, CancellationToken cancellationToken = default(CancellationToken))
@@ -991,8 +990,8 @@ private IBsonSerializer<TField> GetValueSerializerForDistinct<TField>(RenderedFi
 
         private Task<TResult> ExecuteReadOperationAsync<TResult>(IClientSessionHandle session, IReadOperation<TResult> operation, CancellationToken cancellationToken = default(CancellationToken))
         {
-            var readPreference = GetReadPreference(session);
-            return ExecuteReadOperationAsync(session, operation, readPreference, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, null, _settings.ReadPreference);
+            return ExecuteReadOperationAsync(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         private async Task<TResult> ExecuteReadOperationAsync<TResult>(IClientSessionHandle session, IReadOperation<TResult> operation, ReadPreference readPreference, CancellationToken cancellationToken = default(CancellationToken))
@@ -1019,22 +1018,6 @@ private IBsonSerializer<TField> GetValueSerializerForDistinct<TField>(RenderedFi
             }
         }
 
-        private ReadPreference GetReadPreference(IClientSession session)
-        {
-            var readPreference = _settings.ReadPreference;
-
-            if (session.IsInTransaction)
-            {
-                var transactionReadPreference = session.WrappedCoreSession.CurrentTransaction.TransactionOptions.ReadPreference;
-                if (transactionReadPreference != null)
-                {
-                    readPreference = transactionReadPreference;
-                }
-            }
-
-            return readPreference;
-        }
-
         private IEnumerable<BsonDocument> RenderArrayFilters(IEnumerable<ArrayFilterDefinition> arrayFilters)
         {
             if (arrayFilters == null)

src/MongoDB.Driver/MongoDB.Driver.csproj

@@ -304,6 +304,7 @@
     <Compile Include="ProjectionDefinitionBuilder.cs" />
     <Compile Include="IndexKeysDefinitionBuilder.cs" />
     <Compile Include="IServerSession.cs" />
+    <Compile Include="ReadPreferenceResolver.cs" />
     <Compile Include="ServerSession.cs" />
     <Compile Include="SortDefinitionBuilder.cs" />
     <Compile Include="FilterDefinitionBuilder.cs" />

src/MongoDB.Driver/MongoDatabaseImpl.cs

@@ -14,8 +14,6 @@
 */
 
 using System;
-using System.Collections.Generic;
-using System.Linq;
 using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
@@ -203,7 +201,8 @@ public override IAsyncCursor<BsonDocument> ListCollections(IClientSessionHandle
             Ensure.IsNotNull(session, nameof(session));
             options = options ?? new ListCollectionsOptions();
             var operation = CreateListCollectionsOperation(options);
-            return ExecuteReadOperation(session, operation, ReadPreference.Primary, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, null, ReadPreference.Primary);
+            return ExecuteReadOperation(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         public override Task<IAsyncCursor<BsonDocument>> ListCollectionsAsync(ListCollectionsOptions options, CancellationToken cancellationToken)
@@ -216,7 +215,8 @@ public override Task<IAsyncCursor<BsonDocument>> ListCollectionsAsync(IClientSes
             Ensure.IsNotNull(session, nameof(session));
             options = options ?? new ListCollectionsOptions();
             var operation = CreateListCollectionsOperation(options);
-            return ExecuteReadOperationAsync(session, operation, ReadPreference.Primary, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, null, ReadPreference.Primary);
+            return ExecuteReadOperationAsync(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         public override void RenameCollection(string oldName, string newName, RenameCollectionOptions options, CancellationToken cancellationToken)
@@ -260,10 +260,10 @@ public override Task RenameCollectionAsync(IClientSessionHandle session, string
         {
             Ensure.IsNotNull(session, nameof(session));
             Ensure.IsNotNull(command, nameof(command));
-            readPreference = readPreference ?? ReadPreference.Primary;
 
             var operation = CreateRunCommandOperation(command);
-            return ExecuteReadOperation(session, operation, readPreference, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, readPreference, ReadPreference.Primary);
+            return ExecuteReadOperation(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         public override Task<TResult> RunCommandAsync<TResult>(Command<TResult> command, ReadPreference readPreference = null, CancellationToken cancellationToken = default(CancellationToken))
@@ -275,10 +275,10 @@ public override Task RenameCollectionAsync(IClientSessionHandle session, string
         {
             Ensure.IsNotNull(session, nameof(session));
             Ensure.IsNotNull(command, nameof(command));
-            readPreference = readPreference ?? ReadPreference.Primary;
 
             var operation = CreateRunCommandOperation(command);
-            return ExecuteReadOperationAsync(session, operation, readPreference, cancellationToken);
+            var effectiveReadPreference = ReadPreferenceResolver.GetEffectiveReadPreference(session, readPreference, ReadPreference.Primary);
+            return ExecuteReadOperationAsync(session, operation, effectiveReadPreference, cancellationToken);
         }
 
         public override IMongoDatabase WithReadConcern(ReadConcern readConcern)

src/MongoDB.Driver/ReadPreferenceResolver.cs

@@ -0,0 +1,42 @@
+/* Copyright 2018-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.
+*/
+
+namespace MongoDB.Driver
+{
+    internal static class ReadPreferenceResolver
+    {
+        public static ReadPreference GetEffectiveReadPreference(
+            IClientSessionHandle session,
+            ReadPreference explicitReadPreference,
+            ReadPreference defaultReadPreference)
+        {
+            if (explicitReadPreference != null)
+            {
+                return explicitReadPreference;
+            }
+
+            if (session.IsInTransaction)
+            {
+                var transactionReadPreference = session.WrappedCoreSession.CurrentTransaction.TransactionOptions.ReadPreference;
+                if (transactionReadPreference != null)
+                {
+                    return transactionReadPreference;
+                }
+            }
+
+            return defaultReadPreference ?? ReadPreference.Primary;
+        }
+    }
+}