‘Iacta alea est’

Form Formation: Reform (2)

Yesterday I gave a high-level introduction to Trailblazer’s Reform. In the about page of the Trailblazer book, Trailblazer, A New Architecture For Rails, it describes the importance of forms (and Reform) and their responsibilities:

Forms are an integral part of Trailblazer. They orchestrate deserialization of input, population and validation.

Forms are also mentioned as a key element in the Trailblazer architectural style. They can be paired with Trailblazer Operations for maximum effect.

But what does a form look like? As mentioned it is a distinct entity and defining a form class, the basis for a form object, looks like this:

class AlbumForm < Reform::Form
  property :title
  validates :title, presence: true
end

A form field is defined using property. Validations are added to fields using validates. The creation of a form object is done in normal Ruby style and requires a model which the form represents:

form = AlbumForm.new(Album.new)

To validate a form you can call the validate method passing the input data as the parameter:

form.validate(params)

The model remains untouched. The input data is the property of the form at this stage. If #validate returns false then you can fetch errors:

form.errors

These are returned in the Rails’ ActiveModel format. Should #validate return true, and you want to modify the model object, then you can call #sync which updates the object without persisting or #save which syncs and saves in one go.

To render a form you can use the normal view methods but instead of passing a model object you pass the Reform form object:

form_for @form           # Rails default
semantic_form_for @form  # Formtastic
simple_form_for @form    # Simple Form

Where Reform really comes into its own is when there are more complex requirements that go beyond a simple one-to-one mapping between a form and a model object. That’s an avenue for future enquiry.

—Sunday 30th May 2021.