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CSHARP-5658: Convert value type to match field serializer type in Equals filter translation #1981

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CSHARP-5658: Convert value type to match field serializer type in Equals filter translation #1981

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318b932
try to convert value type to match field type before serialization
kyra-rk May 1, 2026
b39159e
add test for equals
kyra-rk May 1, 2026
0158d1c
make testing better
kyra-rk May 1, 2026
44cb8f1
add tests/change names
kyra-rk May 1, 2026
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9 changes: 9 additions & 0 deletions ...slators/ExpressionToFilterTranslators/MethodTranslators/EqualsMethodToFilterTranslator.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
* limitations under the License.
*/

using System;
using System.Linq.Expressions;
using MongoDB.Driver.Linq.Linq3Implementation.Ast.Filters;
using MongoDB.Driver.Linq.Linq3Implementation.ExtensionMethods;
Expand Down Expand Up @@ -72,6 +73,14 @@ private static AstFilter Translate(TranslationContext context, Expression expres

var fieldTranslation = ExpressionToFilterFieldTranslator.Translate(context, fieldExpression);
var value = valueExpression.GetConstantValue<object>(containingExpression: expression);

var serializerValueType = fieldTranslation.Serializer.ValueType;
if (value != null && !serializerValueType.IsInstanceOfType(value))
{
var targetType = Nullable.GetUnderlyingType(serializerValueType) ?? serializerValueType;
value = Convert.ChangeType(value, targetType);
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Copilot AI May 1, 2026

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The new Convert.ChangeType call can throw (InvalidCastException/OverflowException/FormatException) and will currently bubble out of translation without context. Please catch conversion failures here and rethrow an ExpressionNotSupportedException tied to the original expression so users get a consistent LINQ translation error.

Suggested change
value = Convert.ChangeType(value, targetType);
try
{
value = Convert.ChangeType(value, targetType);
}
catch (InvalidCastException)
{
throw new ExpressionNotSupportedException(expression);
}
catch (OverflowException)
{
throw new ExpressionNotSupportedException(expression);
}
catch (FormatException)
{
throw new ExpressionNotSupportedException(expression);
}

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}

var serializedValue = SerializationHelper.SerializeValue(fieldTranslation.Serializer, value);
return AstFilter.Eq(fieldTranslation.Ast, serializedValue);
}
Comment on lines +80 to 86
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Conversion is attempted for any value/type mismatch, which can introduce unintended/culture-dependent conversions (e.g., string->number) rather than failing translation. Consider restricting this conversion to known-safe cases (e.g., numeric/char and nullable numeric via ConvertHelper/TypeExtensions) and leaving other mismatches to fail predictably.

Suggested change
var targetType = Nullable.GetUnderlyingType(serializerValueType) ?? serializerValueType;
value = Convert.ChangeType(value, targetType);
}
var serializedValue = SerializationHelper.SerializeValue(fieldTranslation.Serializer, value);
return AstFilter.Eq(fieldTranslation.Ast, serializedValue);
}
if (!TryConvertKnownSafeValue(value, serializerValueType, out value))
{
throw new ExpressionNotSupportedException(expression);
}
}
var serializedValue = SerializationHelper.SerializeValue(fieldTranslation.Serializer, value);
return AstFilter.Eq(fieldTranslation.Ast, serializedValue);
}
private static bool TryConvertKnownSafeValue(object value, Type serializerValueType, out object convertedValue)
{
var sourceType = value.GetType();
var targetType = Nullable.GetUnderlyingType(serializerValueType) ?? serializerValueType;
if (targetType.IsInstanceOfType(value))
{
convertedValue = value;
return true;
}
if (IsNumericOrCharType(sourceType) && IsNumericOrCharType(targetType))
{
convertedValue = Convert.ChangeType(value, targetType);
return true;
}
convertedValue = null;
return false;
}
private static bool IsNumericOrCharType(Type type)
{
type = Nullable.GetUnderlyingType(type) ?? type;
switch (Type.GetTypeCode(type))
{
case TypeCode.Byte:
case TypeCode.SByte:
case TypeCode.Int16:
case TypeCode.UInt16:
case TypeCode.Int32:
case TypeCode.UInt32:
case TypeCode.Int64:
case TypeCode.UInt64:
case TypeCode.Single:
case TypeCode.Double:
case TypeCode.Decimal:
case TypeCode.Char:
return true;
default:
return false;
}
}

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Expand Down
143 changes: 143 additions & 0 deletions ...rs/ExpressionToFilterTranslators/MethodTranslators/EqualsMethodToFilterTranslatorTests.cs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,143 @@
/* Copyright 2010-present MongoDB Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

using System;
using System.Collections.Generic;
using System.Linq;
using FluentAssertions;
using MongoDB.Driver.TestHelpers;
using Xunit;

namespace MongoDB.Driver.Tests.Linq.Linq3Implementation.Translators.ExpressionToFilterTranslators.MethodTranslators
{
public class EqualsMethodToFilterTranslatorTests : LinqIntegrationTest<EqualsMethodToFilterTranslatorTests.ClassFixture>
{
public EqualsMethodToFilterTranslatorTests(ClassFixture fixture) : base(fixture)
{
}

[Fact]
public void Equals_with_uint64_and_nullable_int32_should_translate()
{
var collection = Fixture.Collection;
ulong value = 2;

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(value));

Comment on lines +37 to +39
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These tests cover field.Equals(constant) but not the supported shape where the constant is the receiver (constant.Equals(field)), which exercises the translator's constant/field swapping logic with the new conversion behavior. Adding at least one test for that form would help prevent regressions.

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var stages = Translate(collection, queryable);
AssertStages(stages, "{ $match : { ReportsTo : 2 } }");

var results = queryable.ToList();
results.Should().HaveCount(1);
results[0].Id.Should().Be(1);
}

[Fact]
public void Equals_with_int32_and_nullable_int32_should_translate()
{
var collection = Fixture.Collection;
int value = 2;

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(value));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $match : { ReportsTo : 2 } }");

var results = queryable.ToList();
results.Should().HaveCount(1);
results[0].Id.Should().Be(1);
}

[Fact]
public void Equals_with_null_and_nullable_int32_should_translate()
{
var collection = Fixture.Collection;

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(null));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $match : { ReportsTo : null } }");

var results = queryable.ToList();
results.Should().HaveCount(1);
results[0].Id.Should().Be(3);
}

[Fact]
public void Equals_with_string_and_nullable_int32_should_throw()
{
var collection = Fixture.Collection;
var value = "2";

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(value));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $match : { ReportsTo : 2 } }");

var results = queryable.ToList();
results.Should().HaveCount(1);
results[0].Id.Should().Be(1);
}

[Fact]
public void Equals_with_no_match_should_return_empty()
{
var collection = Fixture.Collection;
ulong value = 999;

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(value));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $match : { ReportsTo : 999 } }");

var results = queryable.ToList();
results.Should().BeEmpty();
}

[Fact]
public void Equals_with_overflowing_uint64_and_nullable_int32_should_throw()
{
var collection = Fixture.Collection;
ulong value = (ulong)int.MaxValue + 1;

var queryable = collection.AsQueryable()
.Where(e => e.ReportsTo.Equals(value));

var exception = Record.Exception(() => Translate(collection, queryable));
exception.Should().BeOfType<OverflowException>();
}

public class C
{
public int Id { get; set; }
public int? ReportsTo { get; set; }
}

public sealed class ClassFixture : MongoCollectionFixture<C>
{
protected override IEnumerable<C> InitialData =>
[
new C { Id = 1, ReportsTo = 2 },
new C { Id = 2, ReportsTo = 5 },
new C { Id = 3, ReportsTo = null }
];
}
}
}
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