Hello everyone,

When validating anested object using MapRequestPayload, and given payload schema doesn't respect the DTO provided, Symfony serializer throwsPartialDenormalizationException.

Unfortunately theMapRequestPayloadResolver doesn't have enough information about the Dto structure to be able to provide a more detailed error, Instead symfony throws the errors "This value should be of type unknown."

Thisunknown type is originated from theAbstractNormalizer in the serializer component, which injects this value toNotNormalizableValueException class.
I propose to add new Serialization contextAbstractNormalizer::USE_CLASS_AS_DEFAULT_EXPECTED_TYPE,
which allows us to retrieve the class as the expected type for Our DTO if needed.

Example when using the context AbstractNormalizer::USE_CLASS_AS_DEFAULT_EXPECTED_TYPE:

I honestly do not know the reason behind using unkown instead of the FQCN. I find adding a new context more safe, and certainlyBackward compatible to support both usages.

Usage example in a controller:

https://github.com/mmouih/apps-demo/blob/19f9edfa4361567a4b592a32041ead327fb3b898/src/Controller/HomeController.php#L22,L28

I included tests for the new feature:

https://github.com/mmouih/symfony/blob/05ef92028cb75c556ebbf2857617bdf40b8f1643/src/Symfony/Component/HttpKernel/Tests/Controller/ArgumentResolver/RequestPayloadValueResolverTest.php#L288C21-L288C94

Best regards.