Stealing Django form objects for use in Ruby web frameworks

This will become a Ruby implementation of the concepts embodied in Django's form objects. It is also an alternative to Rails' ActiveModel, with several advantages.

This is a play in 3 acts.

Act 1: Form objects (free-standing)

Using Virtus and Aequitas, define objects that support a given form, with typed attributes and validations appropriate to the given input use-case.

Form objects may be used to back a form that triggers work not directly related to any particular persistent model or to create or update several persistent resources.

These form objects correspond with the Django concept of the same name.

Act 2: Model form objects (defined by ORM model reflection)

Any ORM can be supported by defining an adapter that reflects on a persistent model and generates a form object.

The generated form object can be configured to:

1. accept a specified subset of the persistent model's total fields (subsumes attr_accessible functionality).

2. validate according to the model or differently (subsumes many uses of contextual validations)

3. build nested/dependent objects from a single form.

TODO: How to support related objects remains to be defined. This should eventually encompass both 'Embedded Value' and accepts_nested_attributes use-cases

1. serve as a home for business logic around a given data interaction (eg., Forms::UserSignup, which could create a User and send a welcome message)

Act 3: Form builders for producing different kinds of forms

Form builders will be initialized with a form object and will reflect on the attributes defined for it. Each form object has a 1-to-1 mapping with a given form (input use-case), so the form builder can be a simple implementation of the Builder pattern.

The first form builder will produce minimal but valid HTML4 form markup. A future HTML5 form builders will emit markup using HTML5 date/time/number/url, etc elements (with min/max/step/pattern attributes), and could also include data attributes to configure (arbitrarily complex) client-side validation logic.

Credits

Thanks to Django for the useful abstraction to steal.

Inspired by a remark from Yehuda Katz's presentation at GoGaRuCo 2011.