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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
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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
64 changes: 59 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 +284,36 @@ private static bool TryTranslateDictionaryProperty(TranslationContext context, M
translatedDictionaryProperty = null;
return false;
}

private static bool TryTranslateKeyValuePairProperty(MemberExpression expression, TranslatedExpression container, MemberInfo memberInfo, out TranslatedExpression result)
{
result = null;
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@rstam rstam Dec 13, 2025

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I don't like assigning null to out variables at the beginning of the method.

I realize it makes it more convenient to return false, but it also disables the compiler warning you get if you try to return true without setting an out parameter.

Your call.


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?

{
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;
}

return false;
}
}
}
17 changes: 16 additions & 1 deletion ...ExpressionTranslators/MethodTranslators/AverageMethodToAggregationExpressionTranslator.cs
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Expand Up @@ -21,6 +21,7 @@
using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
using MongoDB.Driver.Linq.Linq3Implementation.Misc;
using MongoDB.Driver.Linq.Linq3Implementation.Reflection;
using MongoDB.Driver.Linq.Linq3Implementation.Serializers;

namespace MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToAggregationExpressionTranslators.MethodTranslators
{
Expand Down Expand Up @@ -123,7 +124,21 @@ public static TranslatedExpression Translate(TranslationContext context, MethodC
}
else
{
ast = AstExpression.Avg(sourceTranslation.Ast);
var sourceItemSerializer = ArraySerializerHelper.GetItemSerializer(sourceTranslation.Serializer);
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@rstam rstam Dec 13, 2025

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There is similar code in the translators for Max, Min and Sum.

Is there any way to share the code?

No problem if not.

if (sourceItemSerializer is IWrappedValueSerializer wrappedValueSerializer)
{
var itemVar = AstExpression.Var("item");
var unwrappedItemAst = AstExpression.GetField(itemVar, wrappedValueSerializer.FieldName);
ast = AstExpression.Avg(
AstExpression.Map(
input: sourceTranslation.Ast,
@as: itemVar,
@in: unwrappedItemAst));
}
else
{
ast = AstExpression.Avg(sourceTranslation.Ast);
}
}
IBsonSerializer serializer = expression.Type switch
{
Expand Down
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
49 changes: 49 additions & 0 deletions ...xpressionTranslators/MethodTranslators/ContainsMethodToAggregationExpressionTranslator.cs
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Expand Up @@ -13,6 +13,7 @@
* limitations under the License.
*/

using System.Collections.Generic;
using System.Linq.Expressions;
using MongoDB.Bson.Serialization.Serializers;
using MongoDB.Driver.Linq.Linq3Implementation.Ast.Expressions;
Expand All @@ -33,6 +34,11 @@ public static TranslatedExpression Translate(TranslationContext context, MethodC

if (IsEnumerableContainsMethod(expression, out var sourceExpression, out var valueExpression))
{
if (TryTranslateDictionaryKeysOrValuesContains(context, expression, sourceExpression, valueExpression, out var dictionaryTranslation))
{
return dictionaryTranslation;
}

return TranslateEnumerableContains(context, expression, sourceExpression, valueExpression);
}

Expand Down Expand Up @@ -83,5 +89,48 @@ private static TranslatedExpression TranslateEnumerableContains(TranslationConte

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

private static bool TryTranslateDictionaryKeysOrValuesContains(
TranslationContext context,
Expression expression,
Expression sourceExpression,
Expression valueExpression,
out TranslatedExpression translation)
{
translation = null;
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@rstam rstam Dec 13, 2025

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Same comment as above about assigning null to out parameter at top of method.


if (sourceExpression is not MemberExpression memberExpression)
{
return false;
}

var memberName = memberExpression.Member.Name;
var declaringType = memberExpression.Member.DeclaringType;

if (!declaringType.IsGenericType ||
(declaringType.GetGenericTypeDefinition() != typeof(Dictionary<,>) &&
declaringType.GetGenericTypeDefinition() != typeof(IDictionary<,>)))
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@rstam rstam Dec 13, 2025

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110-112 might be simpler like this:

if (!declaringType.ImplementsDictionaryInterface(out var keyType, out var valueType))

also: test with IReadOnlyDictionary

{
return false;
}

switch (memberName)
{
case "Keys":
{
var dictionaryExpression = memberExpression.Expression;
translation = ContainsKeyMethodToAggregationExpressionTranslator.TranslateContainsKey(context, expression, dictionaryExpression, valueExpression);
return true;
}
case "Values":
{
var dictionaryExpression = memberExpression.Expression;
translation = ContainsValueMethodToAggregationExpressionTranslator.TranslateContainsValue(context, expression, dictionaryExpression, valueExpression);
return true;
}
default:
return false;
}
}
}
}
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