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

Inizia in lib/jsonapi/resource.rb, in _create_to_many_links intorno alla riga 280, dove l’issue segnala che il modello di join viene salvato immediatamente. Esegui o esamina la spec che fallisce del commit 928485a4ea071edf164e954496c06b0de314d555; il lavoro è completato quando gli errori di validazione producono una risposta 422 con una risposta di errore JSON:API formattata correttamente invece di una 500.