The SerializerFinder's CreateCollectionSerializerFromItemSerializer in SerializerFinderHelperMethods.cs creates IQueryableSerializer for all IQueryable<> types. However, when the result is from a nested array operation (e.g., x.A.AsQueryable().Select(...) or x.B.AsQueryable().SelectMany(...)), the translator needs a NestedAsQueryableSerializer (which implements the INestedAsQueryableSerializer marker interface). This marker is required by NestedAsQueryableHelper.EnsureQueryableMethodHasNestedAsQueryableSource for downstream Queryable method chaining.
Because of this mismatch, the translators for Select and SelectMany cannot use context.GetSerializer(expression) for their result serializers and must construct the correct NestedAsQueryableSerializer ad-hoc via NestedAsQueryableSerializer.CreateIEnumerableOrNestedAsQueryableSerializer.
To fully align with the architectural direction of having all serializer information come from the known serializer map, the SerializerFinder would need to be taught the distinction between top-level IQueryable (from the database/pipeline) and nested AsQueryable() (from a nested array), so it can produce the correct serializer type.
Found during CSHARP-5847 implementation.
- related to
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CSHARP-5975 LINQ translators should get lambda parameter serializers from context instead of deriving ad-hoc
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- Backlog
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