Validation Scopes

This gem adds a simple class method validation_scope to ActiveRecord. This generates a new collection of ActiveRecord::Errors that can be manipulated independently of the standard errors, valid? and save methods. The full power of ActiveRecord validations are preserved in these distinct error collections, including all the macros.

For example, in addition to standard errors that prevent an object from being saved to the database, you may want a second collection of warnings that you display to the user or otherwise shape the control flow:

class Film < ActiveRecord::Base
  validates_presence_of :title # Standard errors

  validation_scope :warnings do |s|
    s.validate :ensure_title_is_capitalized
    s.validate { |r| r.warnings.add_to_base("Inline warning") }
    s.validates_presence_of…
    s.validates_inclusion_of…
    s.validates_each…
    s.validates_on_create…
  end

  def ensure_title_is_capitalized
    warnings.add(:title, "should be capitalized") unless title =~ %r{\A[A-Z]}
  end
end

The generated scope produces 3 helper methods based on the symbol passed to the validation_scope method. Continuing the previous example:

film = Film.new(:title => 'lowercase title')
film.valid?
=> true

film.no_warnings?   # analagous to valid?
=> false

film.has_warnings?  # analagous to invalid?
=> true

film.warnings       # analagous to film.errors
=> #<ActiveRecord::Errors>

film.warnings.full_messages
=> ["Title should be capitalized", "Inline warning"]

film.errors.full_messages
=> []

film.class.all_scopes
=> [:warnings]

film.save
=> true

One rough edge at the moment is when you want to use the builtin error_messages_for helper in your views. That helper does not accept an ActiveRecord::Errors object directly. Instead you need to pass it the proxy object that ValidationScopes creates to encapsulate the generated error set:

error_messages_for :object => film.validation_scope_proxy_for_warnings

Compatibility

The current version should work for Rails >= 3.0 and Ruby >= 1.9.2.

For Rails 3 and Ruby 1.8.x use version 0.4.x, however beware there is a memory leak in this version as described here

For Rails 2 see the 0.3.x version of the gem which is maintained on the rails2 branch

Why no Ruby 1.8.7 support? Because fixing the memory leak was easy in Ruby 1.9 by removing the deferred proxy class definition, however this does not work in Ruby 1.8.7 because the ActiveRecord objects methods are not found. The development of this was described in a blog article about the design process. I didn't take the time to figure out why this started working in Ruby 1.9.x (smells like something to do with instance_eval) but it does, and I have no inclination to fix issues in 1.8.x anymore. If you happen to know why offhand though, I'd be glad to hear the reason.

Installation

The usual:

gem install validation_scopes

In your Gemfile:

gem 'validation_scopes'

Or old-school-Rails-style, in your environment.rb:

config.gem 'validation_scopes'

Outside of Rails:

require 'validation_scopes'

Don't use private methods

Because the any validation method supplied as a symbol (eg. validate :verify_something) is actually running in the context of a delegate class, private methods won't work as they would in standard validations.

TODO

• In Rails 3 validations are no longer coupled to ActiveRecord. Although the current version of the gem uses ActiveModel, it hasn't been tested against arbitrary objects.

Copyright

Copyright (c) 2010-2013 Gabe da Silveira. See LICENSE for details.