title: Reform gem to create Devise user nested within Checklist resource -- is this possible?
body: <p>I'm trying to create an event planning checklist app using Devise for the user model, the Reform gem, and simple_form.</p>
  
  <p>I keep seeing this error message when I access the '/new_checklist' path: <strong>undefined method `event_date' for #&lt; Hash:0x007fb18f5b71a8 ></strong>.</p>
  
  <p>What am I doing wrong? For various reasons, I have my user resource nested within my checklist resource.</p>
  
  <p>Here's my event checklist controller:</p>
  
  <pre><code>def new_checklist
    @form = EventChecklistForm.new(event_checklist: EventChecklist.new,
                              user: User.new)
  end
  </code></pre>
  
  <p>User model:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
    devise :database_authenticatable, :registerable,
           :recoverable, :rememberable, :trackable, :validatable
    require 'securerandom'
    has_many :checklist_items
    belongs_to :event_checklist
  end
  </code></pre>
  
  <p>Checklist model:</p>
  
  <pre><code>class EventChecklist &lt; ActiveRecord::Base
    has_many :checklist_items
    has_many :users
    accepts_nested_attributes_for :checklist_items
  end
  </code></pre>
  
  <p>Event checklist form model:</p>
  
  <pre><code>class EventChecklistForm &lt; Reform::Form
    # include DSL
    include Reform::Form::ActiveRecord
  
    property :event_date, on: :event_checklist
    property :code, on: :event_checklist
  
    property :email, on: :user
    property :password, on: :user
    property :password_confirmation, on: :user
  end
  </code></pre>
  
  <p>I've also tried adding "model :event_checklist" to the end of the event checklist model, but it didn't make a difference.</p>
  
  <p>And finally, the form:</p>
  
  <pre><code>= simple_form_for @form do |f|
  
    = f.input :event_date
    = f.input :code
    = f.input :email
    = f.input :password
    = f.input :password_confirmation
  </code></pre>
  
  <p>I had hoped to nest the Devise user model within the event checklist model, and create both at the same time using the Reform gem. Can this not be done? Thanks! </p>