Using p.S.Count() == n in a LINQ query where p.S is of type string was erroneously mapping to an array length query. Now it is treated as an alternative for p.S.Length == n.

Author: rstam

Driver/Linq/Translators/SelectQuery.cs

@@ -19,6 +19,7 @@
 using System.Collections.ObjectModel;
 using System.Linq;
 using System.Linq.Expressions;
+using System.Reflection;
 using System.Text;
 using System.Text.RegularExpressions;
 
@@ -249,49 +250,40 @@ private IMongoQuery BuildArrayLengthQuery(Expression variableExpression, Express
             {
                 return null;
             }
+            var value = ToInt32(constantExpression);
 
             BsonSerializationInfo serializationInfo = null;
-            var value = ToInt32(constantExpression);
 
             var unaryExpression = variableExpression as UnaryExpression;
-            if (unaryExpression != null)
+            if (unaryExpression != null && unaryExpression.NodeType == ExpressionType.ArrayLength)
             {
-                if (unaryExpression.NodeType == ExpressionType.ArrayLength)
+                var arrayMemberExpression = unaryExpression.Operand as MemberExpression;
+                if (arrayMemberExpression != null)
                 {
-                    var memberExpression = unaryExpression.Operand as MemberExpression;
-                    if (memberExpression != null)
-                    {
-                        serializationInfo = GetSerializationInfo(memberExpression);
-                    }
+                    serializationInfo = GetSerializationInfo(arrayMemberExpression);
                 }
             }
 
-            var countPropertyExpression = variableExpression as MemberExpression;
-            if (countPropertyExpression != null)
+            var memberExpression = variableExpression as MemberExpression;
+            if (memberExpression != null && memberExpression.Member.Name == "Count")
             {
-                if (countPropertyExpression.Member.Name == "Count")
+                var arrayMemberExpression = memberExpression.Expression as MemberExpression;
+                if (arrayMemberExpression != null)
                 {
-                    var memberExpression = countPropertyExpression.Expression as MemberExpression;
-                    if (memberExpression != null)
-                    {
-                        serializationInfo = GetSerializationInfo(memberExpression);
-                    }
+                    serializationInfo = GetSerializationInfo(arrayMemberExpression);
                 }
             }
 
-            var countMethodCallExpression = variableExpression as MethodCallExpression;
-            if (countMethodCallExpression != null)
+            var methodCallExpression = variableExpression as MethodCallExpression;
+            if (methodCallExpression != null && methodCallExpression.Method.Name == "Count" && methodCallExpression.Method.DeclaringType == typeof(Enumerable))
             {
-                if (countMethodCallExpression.Method.Name == "Count")
+                var arguments = methodCallExpression.Arguments.ToArray();
+                if (arguments.Length == 1)
                 {
-                    var arguments = countMethodCallExpression.Arguments.ToArray();
-                    if (arguments.Length == 1)
+                    var arrayMemberExpression = methodCallExpression.Arguments[0] as MemberExpression;
+                    if (arrayMemberExpression != null && arrayMemberExpression.Type != typeof(string))
                     {
-                        var memberExpression = countMethodCallExpression.Arguments[0] as MemberExpression;
-                        if (memberExpression != null)
-                        {
-                            serializationInfo = GetSerializationInfo(memberExpression);
-                        }
+                        serializationInfo = GetSerializationInfo(arrayMemberExpression);
                     }
                 }
             }
@@ -756,23 +748,30 @@ private IMongoQuery BuildStringLengthQuery(Expression variableExpression, Expres
             {
                 return null;
             }
+            var value = ToInt32(constantExpression);
 
             BsonSerializationInfo serializationInfo = null;
-            var value = ToInt32(constantExpression);
 
-            var lengthPropertyExpression = variableExpression as MemberExpression;
-            if (lengthPropertyExpression != null)
+            var memberExpression = variableExpression as MemberExpression;
+            if (memberExpression != null && memberExpression.Member.Name == "Length")
             {
-                if (lengthPropertyExpression.Member.Name == "Length")
+                var stringMemberExpression = memberExpression.Expression as MemberExpression;
+                if (stringMemberExpression != null && stringMemberExpression.Type == typeof(string))
                 {
-                    var memberExpression = lengthPropertyExpression.Expression as MemberExpression;
-                    if (memberExpression != null)
+                    serializationInfo = GetSerializationInfo(stringMemberExpression);
+                }
+            }
+
+            var methodCallExpression = variableExpression as MethodCallExpression;
+            if (methodCallExpression != null && methodCallExpression.Method.Name == "Count" && methodCallExpression.Method.DeclaringType == typeof(Enumerable))
+            {
+                var args = methodCallExpression.Arguments.ToArray();
+                if (args.Length == 1)
+                {
+                    var stringMemberExpression = args[0] as MemberExpression;
+                    if (stringMemberExpression != null && stringMemberExpression.Type == typeof(string))
                     {
-                        serializationInfo = GetSerializationInfo(memberExpression);
-                        if (serializationInfo != null && serializationInfo.NominalType != typeof(string))
-                        {
-                            serializationInfo = null;
-                        }
+                        serializationInfo = GetSerializationInfo(stringMemberExpression);
                     }
                 }
             }

DriverUnitTests/Linq/SelectQueryTests.cs

@@ -4282,6 +4282,29 @@ where c.S.Contains(".")
             Assert.AreEqual(0, Consume(query));
         }
 
+        [Test]
+        public void TestWhereSCountEquals3()
+        {
+            var query = from c in _collection.AsQueryable<C>()
+                        where c.S.Count() == 3
+                        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) => (Enumerable.Count<Char>(c.S) == 3)", ExpressionFormatter.ToString(selectQuery.Where));
+            Assert.IsNull(selectQuery.OrderBy);
+            Assert.IsNull(selectQuery.Projection);
+            Assert.IsNull(selectQuery.Skip);
+            Assert.IsNull(selectQuery.Take);
+
+            Assert.AreEqual("{ \"s\" : /^.{3}$/s }", selectQuery.BuildQuery().ToJson());
+            Assert.AreEqual(1, Consume(query));
+        }
+
         [Test]
         public void TestWhereSEndsWithAbc()
         {