Support foreign_type in has_one association

I am updating an app to use jsonapi:resources and have had to change a model association name without changing the underlying table. This model had a polymorphic field :resource which is now called :item, however the underlying table still has fields resource_id and resource_type.

In my model I can do this:

belongs_to :item, polymorphic: true, foreign_key: "resource_id", foreign_type: "resource_type"

However when I do this in my resource file:

has_one :item, polymorphic: true, foreign_key: 'resource_id', foreign_type: 'resource_type'

I receive an error "undefined method item_type=". From the docs it looks like foreign_key is supported but foreign_type is not. Could this be easily fixed?

Thanks for a great gem, it's been a pleasure to work with!

Inizia dalla gestione dell’associazione has_one e dal supporto esistente per foreign_key, quindi riproduci le configurazioni del modello e della risorsa mostrate nell’issue. Il lavoro è completo quando foreign_type viene accettato senza chiamare il metodo non definito item_type=, con una copertura per le associazioni polimorfiche il cui nome del modello differisce dalla colonna del tipo sottostante.