AssociationTypeMismatch, different versions of a class loaded

Could you share your view and controller code please ?

Making use of CanCan and Formtastic:

app/controllers/jobs_controller.rb:

class JobsController < ApplicationController
  before_filter :authenticate_user!, :require_user_has_a_company, :only => [:new, :create]
  load_and_authorize_resource :company
  load_and_authorize_resource :through => :company

  def index
    @jobs = Job.new_to_old.all :include => :company
  end

  def new
    @company = current_user.company
  end

  def create
    @job.company = current_user.company
    if @job.save
      redirect_to [@company, @job], :notice => "Job successfully saved"
    else
      render :action => :new
    end
  end

  def update
    if @job.update_attributes(params[:job])
      redirect_to [@company, @job], :notice => "Job successfully saved"
    else
      render :action => :edit
    end
  end
end

app/views/jobs/edit.html.haml:

- title "Edit a job"
= render 'form'

app/views/jobs/_form.html.haml:

= semantic_form_for [@church, @job] do |form|
  = form.inputs do
    = form.input :tagline, :hint => "Describe what you're looking for in one sentence"
    = form.input :job_titles, :as => :check_boxes
    = form.input :description
  = form.buttons do
    = form.commit_button 'Save job'

HTML output of app/views/edit.html.haml:

<form accept-charset="UTF-8" action="/churches/14/jobs/16" class="formtastic job" id="edit_job_16" method="post"><div style="margin:0;padding:0;display:inline"><input name="utf8" type="hidden" value="&#x2713;" /><input name="_method" type="hidden" value="put" /><input name="authenticity_token" type="hidden" value="f/aSr9QKidvCVv0+83HoI7Za+6PdXPQBL3aQpR5KQGY=" /></div>
    <fieldset class="inputs"><ol><li class="string optional" id="job_tagline_input"><label for="job_tagline">Tagline</label><input id="job_tagline" maxlength="255" name="job[tagline]" size="50" type="text" value="Awesome job of awesome! :)" /> 
  <p class="inline-hints">Describe what you're looking for in one sentence</p></li> 
  <li class="check_boxes optional" id="job_job_titles_input"><fieldset><legend class="label"><label>Job titles</label></legend><input id="job_job_title_ids_" name="job[job_title_ids][]" type="hidden" value="" /><ol><li><label for="job_job_title_ids_3"><input id="job_job_title_ids_3" name="job[job_title_ids][]" type="checkbox" value="3" /> Big boss</label></li><li><label for="job_job_title_ids_4"><input checked="checked" id="job_job_title_ids_4" name="job[job_title_ids][]" type="checkbox" value="4" /> Secretary</label></li><li><label for="job_job_title_ids_1"><input checked="checked" id="job_job_title_ids_1" name="job[job_title_ids][]" type="checkbox" value="1" /> Code monkey</label></li></ol></fieldset></li> 
  <li class="text required" id="job_description_input"><label for="job_description">Description<abbr title="required">*</abbr></label><textarea cols="50" id="job_description" name="job[description]" rows="20">You better be awesome to get this job. Just saying.</textarea></li> 
  </ol></fieldset> 
  <fieldset class="buttons"><ol><li class="commit"><input class="update" id="job_submit" name="commit" type="submit" value="Save job" /></li> 
  </ol></fieldset> 
</form>

It's tempting to say that CanCan or Formtastic is the culprit, but Formtastic produces the form HTML I'd expect, and the relevant bit of the update action in the controller is still @job.update_attributes(params[:job]). (CanCan doesn't perform the update on its own in load_and_authorize_resource as it does for the initialization; I used the Rails logger to confirm.)

I also, just for testing purposes, added @job.job_title_ids = ['', '1', '3'] to the top of the update action. The error was thrown from that line, instead. This helps narrow down where the issue is by confirmed that it's the actual job_title_ids setter that is the issue, and confirms that it doesn't have to do with the params object performing any strange magic.

Thanks!

Wow, yes. Didn't expect that to be a factor.

Good to see that there's an official patch, and that I'm not just totally going crazy. Ticket ready to be closed.

Thanks!