CSHARP-4423: LinqProvider.V3 Odata filter problem with id filter (#1130)

Author: sanych-sun

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/ConvertExpressionToAggregationExpressionTranslator.cs

@@ -39,6 +39,11 @@ public static AggregationExpression Translate(TranslationContext context, UnaryE
                 var operandExpression = expression.Operand;
                 var operandTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, operandExpression);
 
+                if (expressionType == operandExpression.Type)
+                {
+                    return operandTranslation;
+                }
+
                 if (IsConvertEnumToUnderlyingType(expression))
                 {
                     return TranslateConvertEnumToUnderlyingType(expression, operandTranslation);

src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToFilterTranslators/ToFilterFieldTranslators/ConvertExpressionToFilterFieldTranslator.cs

@@ -34,6 +34,11 @@ public static AstFilterField Translate(TranslationContext context, UnaryExpressi
                 var fieldType = field.Serializer.ValueType;
                 var targetType = expression.Type;
 
+                if (targetType == fieldType)
+                {
+                    return field;
+                }
+
                 if (IsConvertEnumToUnderlyingType(fieldType, targetType))
                 {
                     return TranslateConvertEnumToUnderlyingType(field, targetType);

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/ConvertExpressionToFilterFieldTranslatorTests.cs

@@ -14,6 +14,8 @@
 */
 
 using FluentAssertions;
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
 using MongoDB.Driver.Linq;
 using Xunit;
 
@@ -22,7 +24,7 @@ namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Translators.ExpressionTo
     public class ConvertExpressionToFilterFieldTranslatorTests : Linq3IntegrationTest
     {
         [Fact]
-        public void Should_translate_to_derived_class_on_method_call()
+        public void Projection_using_convert_to_derived_class_with_field_expression_should_work()
         {
             var collection = GetCollection();
 
@@ -39,12 +41,11 @@ public void Should_translate_to_derived_class_on_method_call()
                 "{ '$project' : { _id : '$_id', A : { '$toUpper' : '$A' } } }");
 
             var result = queryable.Single();
-            result.Id.Should().Be(1);
             result.A.Should().Be("TEST VALUE");
         }
 
         [Fact]
-        public void Should_translate_to_derived_class_on_projection()
+        public void Projection_using_convert_to_derived_class_should_work()
         {
             var collection = GetCollection();
 
@@ -61,24 +62,41 @@ public void Should_translate_to_derived_class_on_projection()
                 "{ '$project' : { _id : '$_id', A : '$A' } }");
 
             var result = queryable.Single();
-            result.Id.Should().Be(1);
             result.A.Should().Be("test value");
         }
 
+        [Fact]
+        public void Filter_using_string_as_objectid_should_work()
+        {
+            var collection = GetCollection();
+            var queryable = collection.AsQueryable()
+                // do not remove this extra unnecessary convert to string, it's important to reproduce the issue
+                .Where(i => ((string)i.Id) == "000000000000000000000001");
+
+            var stages = Translate(collection, queryable);
+            AssertStages(
+                stages,
+                "{ $match : { _id : ObjectId('000000000000000000000001') } }");
+
+            var result = queryable.Single();
+            result.Id.Should().Be("000000000000000000000001");
+        }
+
         private IMongoCollection<BaseClass> GetCollection()
         {
             var collection = GetCollection<BaseClass>("test");
             CreateCollection(collection, new DerivedClass()
             {
-                Id = 1,
+                Id = "000000000000000000000001",
                 A = "test value"
             });
             return collection;
         }
 
         private class BaseClass
         {
-            public int Id { get; set; }
+            [BsonRepresentation(BsonType.ObjectId)]
+            public string Id { get; set; }
         }
 
         private class DerivedClass : BaseClass