Responders don't use valid? to check for errors in models to figure out if the request was successful or not, and relies on your controllers to call save or create to trigger the validations.

ActiveInteraction type checks your inputs. Often you'll want more than that. For instance, you may want an input to be a string with at least one non-whitespace character. Instead of writing your own validation for that, you can use validations from ActiveModel. These validations aren't provided by ActiveInteraction. They're from ActiveModel. You can also use any custom validations you wrote yourself in your interactions.

Note that it's perfectly fine to add errors during execution. Not all errors have to come from type checking or validation.

with ActiveForm-Rails, validations is the responsability of the form and not of the models. There is no need to synchronize errors from the form to the models and vice versa.

I agre with your concern. I realy prefer to do this : form.assign_attributes(hash) if form.valid? my_service.update(form) #render something else #render somthing else end It looks more like a normal controller.

My only concern with this approach is that if someone calls #valid? on the form object afterwards, it would under the hood currently delete the existing errors on the form object and revalidate. The could have unexpected side effects where the errors added by the models passed in or the service called will be lost.

My concern with this approach is still that it's somewhat brittle with the current implementation of valid? because whilst valid? appears to be a predicate and should have no side effects, this is not the case and could remove the errors applied by one of the steps above.

Some developers found work arounds by using virtual attributes to # skip validators

Any attribute in the list will be allowed, and any defined as attr_{accessor,reader,writer} will not be populated when passed in as params. This means we no longer need to use strong_params in the controllers because the form has a clear definition of what it expects and protects us by design.

If you include ActiveModel::Validations you can write the same validators as you would with ActiveRecord. However, in this case, our form is just a collection of Contact objects, which are ActiveRecord and have their own validations. When I save the ContactListForm, it attempts to save all the contacts. In doing so, each contact has its error_messages available.

As mentioned in StateMachines::Machine#state, you can define behaviors, like validations, that only execute for certain states. One important caveat here is that, due to a constraint in ActiveRecord's validation framework, custom validators will not work as expected when defined to run in multiple states.

Responders don't use valid? to check for errors in models to figure out if the request was successful or not, and relies on your controllers to call save or create to trigger the validations.

Arguably, the rails-team's choice of raising ArgumentError instead of validation error is correct in the sense that we have full control over what options a user can select from a radio buttons group, or can select over a select field, so if a programmer happens to add a new radio button that has a typo for its value, then it is good to raise an error as it is an application error, and not a user error. However, for APIs, this will not work because we do not have any control anymore on what values get sent to the server.

When the controller creates the user, instead of adding a validation error to the record, it raises an exception. How to avoid this?

In case anyone wants a hack, here is what I came up with.