CSHARP-1449: LINQ now executes over the synchronous stack.

Author: craiggwilson

src/MongoDB.Driver.Tests/Linq/MongoQueryableTests.cs

@@ -233,6 +233,27 @@ public async Task FirstOrDefaultAsync_with_predicate()
             result.Should().Be(11);
         }
 
+        [Test]
+        public void Enumerable_foreach()
+        {
+            var query = from x in CreateQuery()
+                        select x.M;
+
+            int sum = 0;
+
+            foreach (var item in query)
+            {
+                sum += item.Sum();
+            }
+
+            foreach (var item in query)
+            {
+                sum += item.Sum();
+            }
+
+            sum.Should().Be(50);
+        }
+
         [Test]
         public void GroupBy_method()
         {

src/MongoDB.Driver/Linq/AggregateQueryableExecutionModel.cs

@@ -82,19 +82,25 @@ public override string ToString()
             return sb.ToString();
         }
 
+        internal override object Execute<TInput>(IMongoCollection<TInput> collection, AggregateOptions options)
+        {
+            var pipeline = CreatePipeline<TInput>();
+
+            return collection.Aggregate(pipeline, options, CancellationToken.None);
+        }
+
         internal override Task ExecuteAsync<TInput>(IMongoCollection<TInput> collection, AggregateOptions options, CancellationToken cancellationToken)
         {
-            var pipeline = new BsonDocumentStagePipelineDefinition<TInput, TOutput>(
-                _stages,
-                _outputSerializer);
+            var pipeline = CreatePipeline<TInput>();
 
             return collection.AggregateAsync(pipeline, options, cancellationToken);
         }
 
-        internal override object Execute<TInput>(IMongoCollection<TInput> collection, AggregateOptions options)
+        private BsonDocumentStagePipelineDefinition<TInput, TOutput> CreatePipeline<TInput>()
         {
-            // TODO: modify LINQ to have a sync version of this
-            return new AsyncCursorEnumerableAdapter<TOutput>(ct => ((Task<IAsyncCursor<TOutput>>)ExecuteAsync(collection, options, ct)).GetAwaiter().GetResult(), CancellationToken.None);
+            return new BsonDocumentStagePipelineDefinition<TInput, TOutput>(
+                _stages,
+                _outputSerializer);
         }
     }
 }

src/MongoDB.Driver/Linq/ExecutionPlanBuilder.cs

@@ -15,6 +15,7 @@
 
 using System;
 using System.Linq.Expressions;
+using System.Threading;
 
 namespace MongoDB.Driver.Linq
 {
@@ -28,12 +29,24 @@ public static Expression BuildPlan(Expression provider, QueryableTranslation tra
                 null,
                 Expression.Constant(translation.Model, typeof(QueryableExecutionModel)));
 
+            executor = Expression.Convert(
+                executor,
+                typeof(IAsyncCursor<>).MakeGenericType(translation.Model.OutputType));
+
+            // we have an IAsyncCursor at this point... need to change it into an IEnumerable
+            executor = Expression.Call(
+                typeof(IAsyncCursorExtensions),
+                nameof(IAsyncCursorExtensions.ToEnumerable),
+                new Type[] { translation.Model.OutputType },
+                executor,
+                Expression.Constant(CancellationToken.None));
+
             if (translation.ResultTransformer != null)
             {
                 var lambda = translation.ResultTransformer.CreateAggregator(translation.Model.OutputType);
                 executor = Expression.Invoke(
                     lambda,
-                    Expression.Convert(executor, lambda.Parameters[0].Type));
+                    executor);
             }
 
             return executor;