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CSHARP-5748: Use KeyValuePairSerializer consistently for KeyValuePair #1785

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merged 1 commit into from
Oct 3, 2025
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CSHARP-5748: Use KeyValuePairSerializer consistently for KeyValuePair #1785

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24 changes: 24 additions & 0 deletions src/MongoDB.Bson/Serialization/Serializers/KeyValuePairSerializer.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,30 @@ public interface IKeyValuePairSerializer
BsonType Representation { get; }
}

/// <summary>
/// Static factory class for KeyValuePairSerializers.
/// </summary>
public static class KeyValuePairSerializer
{
/// <summary>
/// Creates a KeyValuePairSerializer.
/// </summary>
/// <param name="representation">The representation.</param>
/// <param name="keySerializer">The key serializer.</param>
/// <param name="valueSerializer">The value Serializer.</param>
/// <returns>A KeyValuePairSerializer.</returns>
public static IBsonSerializer Create(
BsonType representation,
IBsonSerializer keySerializer,
IBsonSerializer valueSerializer)
{
var keyType = keySerializer.ValueType;
var valueType = valueSerializer.ValueType;
var keyValuePairSerializerType = typeof(KeyValuePairSerializer<,>).MakeGenericType(keyType, valueType);
return (IBsonSerializer)Activator.CreateInstance(keyValuePairSerializerType, [representation, keySerializer, valueSerializer]);
}
}

/// <summary>
/// Represents a serializer for KeyValuePairs.
/// </summary>
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35 changes: 8 additions & 27 deletions ...gationExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslator.cs
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Expand Up @@ -16,7 +16,9 @@
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using MongoDB.Bson;
using MongoDB.Bson.Serialization;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;

namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators
Expand All @@ -43,37 +45,16 @@ public static TranslatedExpression Translate(
var keyTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, keyExpression);
var valueTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, valueExpression);

var serializer = CreateResultSerializer(expression.Type, keyTranslation.Serializer, valueTranslation.Serializer, out var keyElementName, out var valueElementName);
var ast = AstExpression.ComputedDocument([
AstExpression.ComputedField(keyElementName, keyTranslation.Ast),
AstExpression.ComputedField(valueElementName, valueTranslation.Ast)
AstExpression.ComputedField("k", keyTranslation.Ast),
AstExpression.ComputedField("v", valueTranslation.Ast)
]);

return new TranslatedExpression(expression, ast, serializer);
}

private static IBsonSerializer CreateResultSerializer(
Type resultType,
IBsonSerializer keySerializer,
IBsonSerializer valueSerializer,
out string keyElementName,
out string valueElementName)
{
var constructorInfo = resultType.GetConstructor([keySerializer.ValueType, valueSerializer.ValueType]);
var classMap = new BsonClassMap(resultType);
classMap.MapConstructor(constructorInfo);
classMap.AutoMap();
var keyMemberMap = classMap.GetMemberMap("Key");
keyElementName = keyMemberMap.ElementName;
keyMemberMap.SetSerializer(keySerializer);
var valueMemberMap = classMap.GetMemberMap("Value");
valueElementName = valueMemberMap.ElementName;
valueMemberMap.SetSerializer(valueSerializer);
classMap.Freeze();
var keySerializer = keyTranslation.Serializer;
var valueSerializer = valueTranslation.Serializer;
var keyValuePairSerializer = KeyValuePairSerializer.Create(BsonType.Document, keySerializer, valueSerializer);

// have to use BsonClassMapSerializer here to mimic the MemberInitExpressionToAggregationExpressionTranslator to avoid risking a behavioral breaking change
var serializerType = typeof(BsonClassMapSerializer<>).MakeGenericType(resultType);
return (IBsonSerializer)Activator.CreateInstance(serializerType, classMap);
return new TranslatedExpression(expression, ast, keyValuePairSerializer);
}
}
}
2 changes: 1 addition & 1 deletion tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp1326Tests.cs
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Expand Up @@ -49,7 +49,7 @@ public void Projection_of_ArrayOfDocuments_dictionary_keys_and_values_should_wor
stages,
"{ $match : { ParentId : { $in : [1, 2, 3] }, Gender : 'Male' } }",
"{ $group : { _id : '$ParentId', _elements : { $push : '$$ROOT' } } }",
"{ $project : { Key : '$_id', Value : '$_elements', _id : 0 } }");
"{ $project : { k : '$_id', v : '$_elements', _id : 0 } }");
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I would not call this a breaking change because it doesn't affect the results of the LINQ query.


var results = aggregate.ToList().OrderBy(x => x.Key).ToList();
results[0].Key.Should().Be(1);
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4 changes: 2 additions & 2 deletions ...nExpressionTranslators/NewKeyValuePairExpressionToAggregationExpressionTranslatorTests.cs
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Expand Up @@ -37,7 +37,7 @@ public void NewKeyValuePair_should_translate()
.Select(d => new KeyValuePair<string,int>("X", d.X));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
AssertStages(stages, "{ $project : { k : 'X', v : '$X', _id : 0 } }");

var result = queryable.Single();
result.Key.Should().Be("X");
Expand All @@ -54,7 +54,7 @@ public void KeyValuePair_Create_should_translate()
.Select(d => KeyValuePair.Create("X", d.X));

var stages = Translate(collection, queryable);
AssertStages(stages, "{ $project : { Key : 'X', Value : '$X', _id : 0 } }");
AssertStages(stages, "{ $project : { k : 'X', v : '$X', _id : 0 } }");

var result = queryable.Single();
result.Key.Should().Be("X");
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