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CSHARP-4443: Add comprehensive dictionary LINQ support for all 3 representations #1804

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bc008db
CSHARP-4443: Add comprehensive dictionary LINQ support for all 3 repr…
adelinowona Oct 31, 2025
462dc1c
add tests and update/remove duplicated tests
adelinowona Oct 31, 2025
205eb56
rebase on main for keys and values work from robert
adelinowona Nov 13, 2025
4c2d0bb
update some mql based on robert's suggestions
adelinowona Nov 13, 2025
f1d98e4
add a new translator for dictionary indexer comparison cases
adelinowona Nov 20, 2025
94484c9
split the tests by representation
adelinowona Nov 26, 2025
a416316
move keys and values tests to CSharp5779Tests.cs
adelinowona Nov 26, 2025
fdb6fa7
rebase on main to pull in the filter limit optimization work
adelinowona Nov 26, 2025
0cb78dd
check filter limit support for indexer access
adelinowona Nov 26, 2025
cf57bad
Address code review feedback
adelinowona Dec 18, 2025
cb800c4
CSHARP-4443: POC of unwrapping wrapped values in TranslateEnumerable.
rstam Jan 2, 2026
5530f89
update Values unwrapping tests
adelinowona Jan 5, 2026
1d1ee9b
add AstSimplifier optimization for $size with maps
adelinowona Jan 6, 2026
2ae6720
allow non-string keys to work with array representations
adelinowona Jan 6, 2026
ac6d457
generalize the $size with maps optimization
adelinowona Jan 12, 2026
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28 changes: 27 additions & 1 deletion 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 +29,22 @@ public interface IKeyValuePairSerializer
BsonType Representation { get; }
}

/// <summary>
/// An extended interface for KeyValuePairSerializer that provides access to key and value serializers.
/// </summary>
public interface IKeyValuePairSerializerV2 : IKeyValuePairSerializer
{
/// <summary>
/// Gets the key serializer.
/// </summary>
IBsonSerializer KeySerializer { get; }

/// <summary>
/// Gets the value serializer.
/// </summary>
IBsonSerializer ValueSerializer { get; }
}

/// <summary>
/// Static factory class for KeyValuePairSerializers.
/// </summary>
Expand Down Expand Up @@ -61,7 +77,7 @@ public static IBsonSerializer Create(
public sealed class KeyValuePairSerializer<TKey, TValue> :
StructSerializerBase<KeyValuePair<TKey, TValue>>,
IBsonDocumentSerializer,
IKeyValuePairSerializer
IKeyValuePairSerializerV2
{
// private constants
private static class Flags
Expand Down Expand Up @@ -191,6 +207,16 @@ public IBsonSerializer<TValue> ValueSerializer
get { return _lazyValueSerializer.Value; }
}

/// <summary>
/// Gets the key serializer.
/// </summary>
IBsonSerializer IKeyValuePairSerializerV2.KeySerializer => KeySerializer;

/// <summary>
/// Gets the value serializer.
/// </summary>
IBsonSerializer IKeyValuePairSerializerV2.ValueSerializer => ValueSerializer;

// public methods
/// <summary>
/// Deserializes a value.
Expand Down
5 changes: 5 additions & 0 deletions src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstExpression.cs
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Expand Up @@ -134,6 +134,11 @@ public static AstExpression ArrayElemAt(AstExpression array, AstExpression index
return new AstBinaryExpression(AstBinaryOperator.ArrayElemAt, array, index);
}

public static AstExpression ArrayToObject(AstExpression arg)
{
return new AstUnaryExpression(AstUnaryOperator.ArrayToObject, arg);
}

public static AstExpression Avg(AstExpression array)
{
return new AstUnaryExpression(AstUnaryOperator.Avg, array);
Expand Down
93 changes: 68 additions & 25 deletions src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Optimizers/AstSimplifier.cs
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Expand Up @@ -452,34 +452,36 @@ public override AstNode VisitMapExpression(AstMapExpression node)

// { $map : { input : { $map : { input : <innerInput>, as : "inner", in : { A : <exprA>, B : <exprB>, ... } } }, as: "outer", in : { F : '$$outer.A', G : "$$outer.B", ... } } }
// => { $map : { input : <innerInput>, as: "inner", in : { F : <exprA>, G : <exprB>, ... } } }
if (node.Input is AstMapExpression innerMapExpression &&
node.As is var outerVar &&
node.In is AstComputedDocumentExpression outerComputedDocumentExpression &&
innerMapExpression.Input is var innerInput &&
innerMapExpression.As is var innerVar &&
innerMapExpression.In is AstComputedDocumentExpression innerComputedDocumentExpression &&
outerComputedDocumentExpression.Fields.All(outerField =>
outerField.Value is AstGetFieldExpression outerGetFieldExpression &&
outerGetFieldExpression.Input == outerVar &&
outerGetFieldExpression.FieldName is AstConstantExpression { Value : BsonString { Value : var matchingFieldName } } &&
innerComputedDocumentExpression.Fields.Any(innerField => innerField.Path == matchingFieldName)))
{
var rewrittenOuterFields = new List<AstComputedField>();
foreach (var outerField in outerComputedDocumentExpression.Fields)
{
var outerGetFieldExpression = (AstGetFieldExpression)outerField.Value;
var matchingFieldName = ((AstConstantExpression)outerGetFieldExpression.FieldName).Value.AsString;
var matchingInnerField = innerComputedDocumentExpression.Fields.Single(innerField => innerField.Path == matchingFieldName);
var rewrittenOuterField = AstExpression.ComputedField(outerField.Path, matchingInnerField.Value);
rewrittenOuterFields.Add(rewrittenOuterField);
}
if (node.Input is AstMapExpression innerMapExpression &&
node.As is var outerVar &&
node.In is AstComputedDocumentExpression outerComputedDocumentExpression &&
innerMapExpression.Input is var innerInput &&
innerMapExpression.As is var innerVar &&
innerMapExpression.In is AstComputedDocumentExpression innerComputedDocumentExpression &&
outerComputedDocumentExpression.Fields.All(outerField =>
outerField.Value is AstGetFieldExpression outerGetFieldExpression &&
outerGetFieldExpression.Input == outerVar &&
outerGetFieldExpression.FieldName is AstConstantExpression { Value : BsonString { Value : var matchingFieldName } } &&
innerComputedDocumentExpression.Fields.Any(innerField => innerField.Path == matchingFieldName)))
{
var rewrittenOuterFields = new List<AstComputedField>();
foreach (var outerField in outerComputedDocumentExpression.Fields)
{
var outerGetFieldExpression = (AstGetFieldExpression)outerField.Value;
var matchingFieldName = ((AstConstantExpression)outerGetFieldExpression.FieldName).Value.AsString;
var matchingInnerField = innerComputedDocumentExpression.Fields.Single(innerField => innerField.Path == matchingFieldName);
var rewrittenOuterField = AstExpression.ComputedField(outerField.Path, matchingInnerField.Value);
rewrittenOuterFields.Add(rewrittenOuterField);
}

var simplified = AstExpression.Map(
input: innerInput,
@as: innerVar,
@in: AstExpression.ComputedDocument(rewrittenOuterFields));
var simplified = AstExpression.Map(
input: innerInput,
@as: innerVar,
@in: AstExpression.ComputedDocument(rewrittenOuterFields));

return Visit(simplified);
return Visit(simplified);
}
}

// { $map : { input : [{ A : <exprA1>, B : <exprB1>, ... }, { A : <exprA2>, B : <exprB2>, ... }, ...], as : "item", in: { F : "$$item.A", G : "$$item.B", ... } } }
Expand Down Expand Up @@ -523,6 +525,32 @@ mappedField.Value is AstGetFieldExpression mappedGetField &&
return Visit(simplified);
}

// { $map : { input : { $map : { input : <array>Expr, as : <innerVar>, in : { ..., fieldName : <fieldExpr>, ... } } }, as : <outerVar>, in : "$$<outerVar>.fieldName" } }
// => { $map : { input : <arrayExpr>, as : <innerVar>, in : <fieldExpr> } }
{
if (node.Input is AstMapExpression innerMap &&
node.As is var outerVar &&
node.In is AstGetFieldExpression outerGetFieldExpression &&
outerGetFieldExpression.Input == outerVar &&
outerGetFieldExpression.FieldName is AstConstantExpression { Value : { BsonType : BsonType.String } } fieldNameExpression &&
fieldNameExpression.Value.AsString is var fieldName &&
innerMap.Input is var arrayExpression &&
innerMap.As is var innerVar &&
innerMap.In is AstComputedDocumentExpression innerComputedDocument &&
innerComputedDocument.Fields.SingleOrDefault(f => f.Path == fieldName) is var computedField &&
computedField != null &&
computedField.Value is var fieldExpr)
{
var simplified =
AstExpression.Map(
input: arrayExpression,
@as: innerVar,
@in: fieldExpr);

return Visit(simplified);
}
}

return base.VisitMapExpression(node);

static AstExpression UltimateGetFieldInput(AstGetFieldExpression getField)
Expand Down Expand Up @@ -656,6 +684,21 @@ item is AstComputedDocumentExpression computedDocumentExpression &&
return AstExpression.ComputedDocument(computedFields);
}

// { $size : { $map : { input : <array>, as : <var>, in : "$$<var>.fieldname" } } } => { $size : <array> }
// { $size : { $map : { input : <array>, as : <var>, in : { arrayElemAt: ... } } } } => { $size : <array> }
// { $size : { $map : { input : <array>, as : <var>, in : { k : { $arrayElemAt : ... }, v : { $arrayElemAt : ... } } } } => { $size : <array> }
if (node.Operator == AstUnaryOperator.Size &&
arg is AstMapExpression mapExpression &&
mapExpression.As is var mapVar &&
((mapExpression.In is AstFieldPathExpression fieldPath &&
fieldPath.Path.StartsWith($"$${mapVar.Name}.")) ||
mapExpression.In is AstBinaryExpression { Operator: AstBinaryOperator.ArrayElemAt } ||
(mapExpression.In is AstComputedDocumentExpression computedDoc &&
computedDoc.Fields.All(f => f.Value is AstBinaryExpression { Operator: AstBinaryOperator.ArrayElemAt }))))
{
return AstExpression.Size(mapExpression.Input);
}

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@rstam rstam Jan 9, 2026

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I think this simplification could be applied more generally:

 // { $size : { map : { input : <array>, as : <var> in : <expr> } } } => { $size : <array> }
 if (node.Operator == AstUnaryOperator.Size &&                                              
     arg is AstMapExpression mapExpression)                                                 
 {                                                                                          
     return AstExpression.Size(mapExpression.Input);                                        
 }

return node.Update(arg);

static AstComputedField KeyValuePairDocumentToComputedField(AstExpression expression)
Expand Down
15 changes: 15 additions & 0 deletions ...pressionToAggregationExpressionTranslators/ExpressionToAggregationExpressionTranslator.cs
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Expand Up @@ -126,6 +126,21 @@ public static TranslatedExpression TranslateEnumerable(TranslationContext contex
aggregateExpression = new TranslatedExpression(expression, ast, arrayOfDocumentsDictionarySerializer);
}

if (aggregateExpression.Serializer is IBsonArraySerializer arraySerializer &&
arraySerializer.TryGetItemSerializationInfo(out var itemSerializationInfo) &&
itemSerializationInfo.Serializer is IWrappedValueSerializer wrappedItemSerializer)
{
var itemVar = AstExpression.Var("item");
var unwrappedItemsAst = AstExpression.Map(
input: aggregateExpression.Ast,
@as: itemVar,
@in: AstExpression.GetField(itemVar, wrappedItemSerializer.FieldName));
var unwrappedItemSerializer = wrappedItemSerializer.ValueSerializer;
var unwrappedItemsSerializer = ArraySerializerHelper.CreateSerializer(unwrappedItemSerializer);

aggregateExpression = new TranslatedExpression(expression, unwrappedItemsAst, unwrappedItemsSerializer);
}

return aggregateExpression;
}

Expand Down
63 changes: 58 additions & 5 deletions ...onToAggregationExpressionTranslators/MemberExpressionToAggregationExpressionTranslator.cs
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Expand Up @@ -14,7 +14,6 @@
*/

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;
Expand Down Expand Up @@ -71,11 +70,16 @@ public static TranslatedExpression Translate(TranslationContext context, MemberE

if (!DocumentSerializerHelper.AreMembersRepresentedAsFields(containerTranslation.Serializer, out _))
{
if (member is PropertyInfo propertyInfo && propertyInfo.Name == "Length")
if (member is PropertyInfo propertyInfo && propertyInfo.Name == "Length")
{
return LengthPropertyToAggregationExpressionTranslator.Translate(context, expression);
}

if (TryTranslateKeyValuePairProperty(expression, containerTranslation, member, out var translatedKeyValuePairProperty))
{
return translatedKeyValuePairProperty;
}

if (TryTranslateCollectionCountProperty(expression, containerTranslation, member, out var translatedCount))
{
return translatedCount;
Expand Down Expand Up @@ -126,11 +130,20 @@ private static bool TryTranslateCollectionCountProperty(MemberExpression express
{
if (EnumerableProperty.IsCountProperty(expression))
{
SerializationHelper.EnsureRepresentationIsArray(expression, container.Serializer);
AstExpression ast;

var ast = AstExpression.Size(container.Ast);
var serializer = Int32Serializer.Instance;
if (container.Serializer is IBsonDictionarySerializer dictionarySerializer &&
dictionarySerializer.DictionaryRepresentation == DictionaryRepresentation.Document)
{
ast = AstExpression.Size(AstExpression.ObjectToArray(container.Ast));
}
else
{
SerializationHelper.EnsureRepresentationIsArray(expression, container.Serializer);
ast = AstExpression.Size(container.Ast);
}

var serializer = Int32Serializer.Instance;
result = new TranslatedExpression(expression, ast, serializer);
return true;
}
Expand Down Expand Up @@ -213,6 +226,16 @@ private static bool TryTranslateDictionaryProperty(TranslationContext context, M

switch (propertyInfo.Name)
{
case "Count":
var countAst = dictionaryRepresentation switch
{
DictionaryRepresentation.ArrayOfDocuments or DictionaryRepresentation.ArrayOfArrays => AstExpression.Size(containerAst),
_ => throw new ExpressionNotSupportedException(expression, $"Unexpected dictionary representation: {dictionaryRepresentation}")
};
var countSerializer = Int32Serializer.Instance;
translatedDictionaryProperty = new TranslatedExpression(expression, countAst, countSerializer);
return true;

case "Keys":
var keysAst = dictionaryRepresentation switch
{
Expand Down Expand Up @@ -261,5 +284,35 @@ private static bool TryTranslateDictionaryProperty(TranslationContext context, M
translatedDictionaryProperty = null;
return false;
}

private static bool TryTranslateKeyValuePairProperty(MemberExpression expression, TranslatedExpression container, MemberInfo memberInfo, out TranslatedExpression result)
{
if (container.Expression.Type.IsGenericType &&
container.Expression.Type.GetGenericTypeDefinition() == typeof(KeyValuePair<,>) &&
container.Serializer is IKeyValuePairSerializerV2 { Representation: BsonType.Array } kvpSerializer)
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@rstam rstam Dec 13, 2025

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Why are we ignoring Document representation here?

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@adelinowona adelinowona Dec 18, 2025

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We're only handling Array representation in TryTranslateKeyValuePairProperty because Document representation is already correctly handled by the general member translation logic that follows (lines
94-108).

That code uses GetMemberSerializationInfo which returns the correct field names ("k" and "v") and serializers for Document-represented KeyValuePairs.

The method is only called when !AreMembersRepresentedAsFields (line 71), which is true for Array representation but false for Document representation.

{
AstExpression ast;
IBsonSerializer serializer;

switch (memberInfo.Name)
{
case "Key":
ast = AstExpression.ArrayElemAt(container.Ast, 0);
serializer = kvpSerializer.KeySerializer;
break;
case "Value":
ast = AstExpression.ArrayElemAt(container.Ast, 1);
serializer = kvpSerializer.ValueSerializer;
break;
default:
throw new ExpressionNotSupportedException(expression);
}
result = new TranslatedExpression(expression, ast, serializer);
return true;
}

result = null;
return false;
}
}
}
54 changes: 42 additions & 12 deletions ...essionTranslators/MethodTranslators/ContainsKeyMethodToAggregationExpressionTranslator.cs
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Expand Up @@ -36,27 +36,57 @@ public static TranslatedExpression Translate(TranslationContext context, MethodC
{
var dictionaryExpression = expression.Object;
var keyExpression = arguments[0];
return TranslateContainsKey(context, expression, dictionaryExpression, keyExpression);
}

throw new ExpressionNotSupportedException(expression);
}

var dictionaryTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, dictionaryExpression);
var dictionarySerializer = GetDictionarySerializer(expression, dictionaryTranslation);
var dictionaryRepresentation = dictionarySerializer.DictionaryRepresentation;
public static TranslatedExpression TranslateContainsKey(TranslationContext context, Expression expression, Expression dictionaryExpression, Expression keyExpression)
{
var dictionaryTranslation = ExpressionToAggregationExpressionTranslator.Translate(context, dictionaryExpression);
var dictionarySerializer = GetDictionarySerializer(expression, dictionaryTranslation);
var dictionaryRepresentation = dictionarySerializer.DictionaryRepresentation;

AstExpression ast;
switch (dictionaryRepresentation)
{
case DictionaryRepresentation.Document:
AstExpression ast;
switch (dictionaryRepresentation)
{
case DictionaryRepresentation.Document:
{
var keyFieldName = GetKeyFieldName(context, expression, keyExpression, dictionarySerializer.KeySerializer);
ast = AstExpression.IsNotMissing(AstExpression.GetField(dictionaryTranslation.Ast, keyFieldName));
break;
}

default:
throw new ExpressionNotSupportedException(expression, because: $"ContainsKey is not supported when DictionaryRepresentation is: {dictionaryRepresentation}");
}
case DictionaryRepresentation.ArrayOfDocuments:
{
var keyFieldName = GetKeyFieldName(context, expression, keyExpression, dictionarySerializer.KeySerializer);
var kvpVar = AstExpression.Var("kvp");
var keysArray = AstExpression.Map(
input: dictionaryTranslation.Ast,
@as: kvpVar,
@in: AstExpression.GetField(kvpVar, "k"));
ast = AstExpression.In(keyFieldName, keysArray);
break;
}

case DictionaryRepresentation.ArrayOfArrays:
{
var keyFieldName = GetKeyFieldName(context, expression, keyExpression, dictionarySerializer.KeySerializer);
var kvpVar = AstExpression.Var("kvp");
var keysArray = AstExpression.Map(
input: dictionaryTranslation.Ast,
@as: kvpVar,
@in: AstExpression.ArrayElemAt(kvpVar, 0));
ast = AstExpression.In(keyFieldName, keysArray);
break;
}

return new TranslatedExpression(expression, ast, BooleanSerializer.Instance);
default:
throw new ExpressionNotSupportedException(expression, because: $"DictionaryRepresentation: {dictionaryRepresentation} is not supported.");
}

throw new ExpressionNotSupportedException(expression);
return new TranslatedExpression(expression, ast, BooleanSerializer.Instance);
}

private static AstExpression GetKeyFieldName(TranslationContext context, Expression expression, Expression keyExpression, IBsonSerializer keySerializer)
Expand Down
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