Finished implementing CSHARP-431. Allow constant on the left in BuildModQuery.

Author: Robert Stam

Driver/Linq/Translators/SelectQuery.cs

@@ -598,26 +598,40 @@ private IMongoQuery BuildMethodCallQuery(MethodCallExpression methodCallExpressi
 
         private IMongoQuery BuildModQuery(BinaryExpression binaryExpression)
         {
-            var leftBinaryExpression = binaryExpression.Left as BinaryExpression;
-            if (leftBinaryExpression != null && leftBinaryExpression.NodeType == ExpressionType.Modulo)
+            // the constant could be on either side
+            var variableExpression = binaryExpression.Left;
+            var constantExpression = binaryExpression.Right as ConstantExpression;
+            if (constantExpression == null)
+            {
+                constantExpression = binaryExpression.Left as ConstantExpression;
+                variableExpression = binaryExpression.Right;
+            }
+
+            if (constantExpression == null || constantExpression.Type != typeof(int))
+            {
+                return null;
+            }
+            var value = ToInt32(constantExpression);
+
+            var modBinaryExpression = variableExpression as BinaryExpression;
+            if (modBinaryExpression != null && modBinaryExpression.NodeType == ExpressionType.Modulo)
             {
-                var serializationInfo = GetSerializationInfo(leftBinaryExpression.Left);
-                var modulusExpression = leftBinaryExpression.Right as ConstantExpression;
-                var equalsExpression = binaryExpression.Right as ConstantExpression;
-                if (serializationInfo != null && modulusExpression != null && equalsExpression != null)
+                var serializationInfo = GetSerializationInfo(modBinaryExpression.Left);
+                var modulusExpression = modBinaryExpression.Right as ConstantExpression;
+                if (serializationInfo != null && modulusExpression != null)
                 {
-                    var modulus = Convert.ToInt32(modulusExpression.Value);
-                    var equals = Convert.ToInt32(equalsExpression.Value);
+                    var modulus = ToInt32(modulusExpression);
                     if (binaryExpression.NodeType == ExpressionType.Equal)
                     {
-                        return Query.Mod(serializationInfo.ElementName, modulus, equals);
+                        return Query.Mod(serializationInfo.ElementName, modulus, value);
                     }
                     else
                     {
-                        return Query.Not(serializationInfo.ElementName).Mod(modulus, equals);
+                        return Query.Not(serializationInfo.ElementName).Mod(modulus, value);
                     }
                 }
             }
+
             return null;
         }
 
@@ -1000,7 +1014,7 @@ private int ToInt32(Expression expression)
                 throw new ArgumentOutOfRangeException("expression", "Expected a ConstantExpression.");
             }
 
-            return (int) constantExpression.Value;
+            return (int)constantExpression.Value;
         }
 
         private void TranslateAny(MethodCallExpression methodCallExpression)

DriverUnitTests/Linq/SelectQueryTests.cs

@@ -5368,6 +5368,29 @@ public void TestWhereXModTwoEquals1Not()
             Assert.AreEqual(2, Consume(query));
         }
 
+        [Test]
+        public void TestWhereXModTwoEquals1Reversed()
+        {
+            var query = from c in _collection.AsQueryable<C>()
+                        where 1 == c.X % 2
+                        select c;
+
+            var translatedQuery = MongoQueryTranslator.Translate(query);
+            Assert.IsInstanceOf<SelectQuery>(translatedQuery);
+            Assert.AreSame(_collection, translatedQuery.Collection);
+            Assert.AreSame(typeof(C), translatedQuery.DocumentType);
+
+            var selectQuery = (SelectQuery)translatedQuery;
+            Assert.AreEqual("(C c) => (1 == (c.X % 2))", ExpressionFormatter.ToString(selectQuery.Where));
+            Assert.IsNull(selectQuery.OrderBy);
+            Assert.IsNull(selectQuery.Projection);
+            Assert.IsNull(selectQuery.Skip);
+            Assert.IsNull(selectQuery.Take);
+
+            Assert.AreEqual("{ \"x\" : { \"$mod\" : [2, 1] } }", selectQuery.BuildQuery().ToJson());
+            Assert.AreEqual(3, Consume(query));
+        }
+
         [Test]
         public void TestWhereXModTwoNotEquals1()
         {