CSHARP-1443: fix issue with no matching documents causing count or sum results of 0 to throw an exception.

Author: craiggwilson

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

@@ -123,6 +123,14 @@ public void Count_with_predicate()
             result.Should().Be(1);
         }
 
+        [Test]
+        public void Count_with_no_matches()
+        {
+            var result = CreateQuery().Count(x => x.C.E.F == 13151235);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         public async Task CountAsync()
         {
@@ -139,6 +147,14 @@ public async Task CountAsync_with_predicate()
             result.Should().Be(1);
         }
 
+        [Test]
+        public async Task CountAsync_with_no_matches()
+        {
+            var result = await CreateQuery().CountAsync(x => x.C.E.F == 123412523);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         [RequiresServer(MinimumVersion = "2.6.0")]
         public void Distinct_followed_by_where()
@@ -364,6 +380,14 @@ public void LongCount_with_predicate()
             result.Should().Be(1);
         }
 
+        [Test]
+        public void LongCount_with_no_results()
+        {
+            var result = CreateQuery().LongCount(x => x.C.E.F == 123452135);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         public async Task LongCountAsync()
         {
@@ -380,6 +404,14 @@ public async Task LongCountAsync_with_predicate()
             result.Should().Be(1);
         }
 
+        [Test]
+        public async Task LongCountAsync_with_no_results()
+        {
+            var result = await CreateQuery().LongCountAsync(x => x.C.E.F == 12351235);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         public void Max()
         {
@@ -1039,6 +1071,14 @@ public void Sum_with_selector()
             result.Should().Be(122);
         }
 
+        [Test]
+        public void Sum_with_no_results()
+        {
+            var result = CreateQuery().Where(x => x.C.E.F == 12341235).Sum(x => x.C.E.F);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         public async Task SumAsync()
         {
@@ -1055,6 +1095,14 @@ public async Task SumAsync_with_selector()
             result.Should().Be(122);
         }
 
+        [Test]
+        public async Task SumAsync_with_no_results()
+        {
+            var result = await CreateQuery().Where(x => x.C.E.F == 21341235).SumAsync(x => x.C.E.F);
+
+            result.Should().Be(0);
+        }
+
         [Test]
         public void Take()
         {

src/MongoDB.Driver/Linq/Expressions/ResultOperators/CountResultOperator.cs

@@ -40,12 +40,12 @@ public override Type Type
 
         public LambdaExpression CreateAggregator(Type sourceType)
         {
-            return ResultTransformerHelper.CreateAggregator("Single", sourceType);
+            return ResultTransformerHelper.CreateAggregator("SingleOrDefault", sourceType);
         }
 
         public LambdaExpression CreateAsyncAggregator(Type sourceType)
         {
-            return ResultTransformerHelper.CreateAsyncAggregator("SingleAsync", sourceType);
+            return ResultTransformerHelper.CreateAsyncAggregator("SingleOrDefaultAsync", sourceType);
         }
     }
 }

src/MongoDB.Driver/Linq/Expressions/ResultOperators/SumResultOperator.cs

@@ -40,12 +40,12 @@ public override Type Type
 
         public LambdaExpression CreateAggregator(Type sourceType)
         {
-            return ResultTransformerHelper.CreateAggregator("Single", sourceType);
+            return ResultTransformerHelper.CreateAggregator("SingleOrDefault", sourceType);
         }
 
         public LambdaExpression CreateAsyncAggregator(Type sourceType)
         {
-            return ResultTransformerHelper.CreateAsyncAggregator("SingleAsync", sourceType);
+            return ResultTransformerHelper.CreateAsyncAggregator("SingleOrDefaultAsync", sourceType);
         }
     }
 }

src/MongoDB.Driver/Linq/MongoQueryProviderImpl.cs

@@ -79,7 +79,14 @@ public object Execute(Expression expression)
                 Translate(expression));
 
             var lambda = Expression.Lambda(executionPlan);
-            return lambda.Compile().DynamicInvoke(null);
+            try
+            {
+                return lambda.Compile().DynamicInvoke(null);
+            }
+            catch (TargetInvocationException tie)
+            {
+                throw tie.InnerException;
+            }
         }
 
         public Task<TResult> ExecuteAsync<TResult>(Expression expression, CancellationToken cancellationToken = default(CancellationToken))