Rails 3: creating a validation with :if statement

Question

Hi I'm trying to setup a validation that is only called in a specific form view, to do this I'm trying to create a hidden_field for a virtual attribute on the form and set this to a value, then validate :if the virtual attribute equals the value.

So far I have:

## user model 

validates_presence_of :password_confirmation, :if => :confirmation_validation 

attr_accessible :email, :password, :password_confirmation, 
 :remember_me, :name, :avatar, :username, :bio, :confirmation_validation

def confirmation_validation
 # not sure what goes here???
end


## form view


<%= form_for(resource, :validate => true, :as => resource_name, :url => registration_path(resource_name), :html => { :method => :put }, :html => {:multipart => true}) do |f| %>
<%= devise_error_messages! %>

<p><%= f.label :password %> <i>(leave blank if you don't want to change it)</i><br />
<%= f.password_field :password %></p>

<p><%= f.label :password_confirmation %><br />
<%= f.password_field :password_confirmation %>
<% f.hidden_field :confirmation_validation, :value => 100%></p>

<p><%= f.submit "Update" %></p>
<% end %>

Answer 1

The value of the confirmation_validation hidden field should be included in the params hash, and also set the virtual attribute accordingly. Therefore, you can probably simply check whether or not the value has been set:

validates_presence_of :password_confirmation, :if => :should_confirm?

def should_confirm?
  confirmation_validation == '100' # Value of the hidden field as set in the form
end