Description

Description
In custom formats, values might be represented the same way, so it is not possible to determine if a value is intended to be a string, int, float or boolean.

If something with non string properties (int, float, bool) is deserialized, an error is thrown (I copied this from the old issue I linked below, so the line-numbers may be outdated):

PHP Fatal error:  Uncaught Symfony\Component\Serializer\Exception\NotNormalizableValueException: The type of the "width" attribute for class "App\Entities\Building" must be one of "float" ("string" given). in ./symfony-serializer-bug/Normalizer/AbstractObjectNormalizer.php:298
Stack trace:
#0 ./symfony-collection-serializer-bug/Normalizer/AbstractObjectNormalizer.php(202): Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->validateAndDenormalize('App\\Entities\\Bu...', 'width', '10.1', 'xml', Array)
#1 ./symfony-collection-serializer-bug/Serializer.php(172): Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->denormalize(Array, 'App\\Entities\\Bu...', 'xml', Array)
#2 ./symfony-collection-serializer-bug/Serializer.php(123): Symfony\Component\Serializer\Serializer->denormalize(Array, 'App\\Entities\\Bu...', 'xml', Array)
...

I've had this issue with XML and CSV in the past (see #33849 and the corresponding PR #33850).

Now I've implemented a custom decoder for multiplart-post-requests, so I can upload files to my api-endpoint (using API Platform and VichUploaderBundle), and the same problem occurs.

How to reproduce

I've used this decoder here: https://api-platform.com/docs/core/file-upload/#handling-the-multipart-deserialization
Basically you need to post some non-string fields and try to deserialize them to an entity, where the parameter of the setter are typed with non-string types (int/float/bool).

Conclusion
Since form/multipart is not natively supported as a format by the serializer, I figured this is more a feature request than a bug report.

But I would love to be able to make this work with custom encoders.

Thank you for your work!

P.S.: Workaround: I've use JSON.stringify and put the json-string in a field inside the multipart-request. In the decoder this field is handled separatly. A bit ugly but it works...

Example

No response