Sidnei da Silva wrote:

Valid in general, invalid in the Archetypes field validation cycle.

Not all CMFFormController validators are used to validate edit forms. In fact, "success" and "failure" are not the only two outcome states possible - it's just an arbitrary string. It may be a bad idea in many cases, but that doesn't mean we should abort the transaction. As Philipp pointed out, this can cause problems later.

We almost never do explicit transaction management (apart from savepoints, which are safe), because it's so much safer and easier to let Zope do the transaction management for us. Let's say someone wanted a write on a validator-failed path (Martin Krafft already said he does), you're proposing we get a commit-then-abort or something equally weird.

For your use case, why don't you just subclass from ReferenceField and override set() to do your object creation? That seems much more in line with how AT fields and widget work (and the very notion of a widget, which to my mind is about presentation only!), relatively easy and doesn't mean changing the fundamental libraries that come with Plone.

Martin