Internal server error when validation fails on a join model

Hello!

I have a model with a has_many :through relationship and a couple of validations on the join model. Whenever the validations fail i get a 500 response, a 422 with a properly formatted jsonapi error response would be preferable. For now i've resorted to using custom exceptions and fail CustomException in the validations so it's catched properly, but that's not ideal.

Problem is, the shovel (<<) method in _create_to_many_links (https://github.com/cerebris/jsonapi-resources/blob/master/lib/jsonapi/resource.rb#L280) is triggering the model's save! immediately, so when it raises ActiveRecord::ValidationFailed it's not catched and interpreted as an internal server error.

Can this be solved, or is there a preferred approach to processing such exceptions?

I've added a failing spec that demonstrates this issue here: https://github.com/needto/jsonapi-resources/commit/928485a4ea071edf164e954496c06b0de314d555

Commencez dans lib/jsonapi/resource.rb, à _create_to_many_links vers la ligne 280, où l’issue signale que le modèle de jointure est enregistré immédiatement. Exécutez ou inspectez la spec en échec du commit 928485a4ea071edf164e954496c06b0de314d555 ; le travail est terminé lorsque les échecs de validation produisent une réponse 422 avec une réponse d’erreur JSON:API correctement formatée au lieu d’une 500.