title: Polymorphic model, Forms and AssociationTypeMismatch
body: <p>i have two models, Content and Page</p>
  
  <pre><code>class Content &lt; ActiveRecord::Base
     attr_accessible :large_description, :short_description
     belongs_to :contentable , :polymorphic =&gt; true
  end
  
  class Page &lt; ActiveRecord::Base
     extend FriendlyId
     friendly_id :title, use: [:slugged, :history]
     attr_accessible :active, :menu, :slug, :title, :contents
  
     validates :title, presence: true
  
     has_many :contents, as: :contentable
  end
  </code></pre>
  
  <p>this is my simple form to create a new page with contents</p>
  
  <pre><code>&lt;%= form_for([:admin,@page], :html =&gt; {:class =&gt; "nice custom"}) do |f| %&gt;
    &lt;div class="formRow"&gt;
      &lt;%= f.label :title, "Title"%&gt;
      &lt;%= f.text_field :title, :class =&gt; 'input-text'%&gt;
    &lt;/div&gt;
  &lt;%= f.fields_for :contents do |content_form| %&gt;
    &lt;div class="formRow"&gt;
     &lt;%= content_form.label :short_description, "Short Description"%&gt;
     &lt;%= content_form.text_area :short_description, :class =&gt; 'tinymce expand'%&gt;
    &lt;/div&gt;
    &lt;div class="formRow"&gt;
      &lt;%= content_form.label :large_description, "Large Description"%&gt;
      &lt;%= content_form.text_area :large_description, :class =&gt; 'tinymce expand'%&gt;
    &lt;/div&gt;
  &lt;% end %&gt;
   &lt;div class="formRow"&gt;
      &lt;%= f.submit "Create", :class =&gt; 'button small nice blue'%&gt;
   &lt;/div&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>and finally this is my page controller</p>
  
  <pre><code>class Admin::PagesController &lt; ApplicationController
    layout 'admin'
    def index
      @pages = Page.order("created_at")
    end
    def new
      @page = Page.new
    end
    def create
      @page = Page.new(params[:page])
      if @page.save
       redirect_to page_url
      else
       render :new
       end
    end
  
    def show
      @page = Page.find(params[:id])
    end
  
    def destroy
      @page = Page.find(params[:id])
      @page.destroy
      redirect_to page_url
    end
  end
  </code></pre>
  
  <p>i have used a namespace Admin.
  so the problem is when i send the form, i receive this error and i don't undersand why have a mismatch:</p>
  
  <blockquote>
    <p>ActiveRecord::AssociationTypeMismatch in Admin::PagesController#create
    Content(#70150608194420) expected, got Array(#70150590276780)</p>
    
    <p>activerecord (3.2.8)
    lib/active_record/associations/association.rb:204:in
    <code>raise_on_type_mismatch' activerecord (3.2.8)
    lib/active_record/associations/collection_association.rb:308:in</code>block
    in replace' activerecord (3.2.8)
    lib/active_record/associations/collection_association.rb:308:in <code>each'
    activerecord (3.2.8)
    lib/active_record/associations/collection_association.rb:308:in
    </code>replace' activerecord (3.2.8)
    lib/active_record/associations/collection_association.rb:41:in
    <code>writer' activerecord (3.2.8)
    lib/active_record/associations/builder/association.rb:51:in</code>block in
    define_writers' activerecord (3.2.8)
    lib/active_record/attribute_assignment.rb:94:in <code>block in
    assign_attributes' activerecord (3.2.8)
    lib/active_record/attribute_assignment.rb:93:in</code>each' activerecord
    (3.2.8) lib/active_record/attribute_assignment.rb:93:in
    <code>assign_attributes' activerecord (3.2.8)
    lib/active_record/base.rb:498:in</code>initialize'
    app/controllers/admin/pages_controller.rb:13:in <code>new'
    app/controllers/admin/pages_controller.rb:13:in</code>create' actionpack
    (3.2.8) lib/action_controller/metal/implicit_render.rb:4:in
    <code>send_action' actionpack (3.2.8)
    lib/abstract_controller/base.rb:167:in</code>process_action' actionpack
    (3.2.8) lib/action_controller/metal/rendering.rb:10:in
    <code>process_action' actionpack (3.2.8)
    lib/abstract_controller/callbacks.rb:18:in</code>block in process_action'
    activesupport (3.2.8) lib/active_support/callbacks.rb:414:in
    <code>_run__3558390125630086563__process_action__2004224720818030891__callbacks' activesupport (3.2.8) lib/active_support/callbacks.rb:405:in
    </code>__run_callback' activesupport (3.2.8)
    lib/active_support/callbacks.rb:385:in <code>_run_process_action_callbacks'
    activesupport (3.2.8) lib/active_support/callbacks.rb:81:in
    </code>run_callbacks' actionpack (3.2.8)
    lib/abstract_controller/callbacks.rb:17:in <code>process_action' actionpack
    (3.2.8) lib/action_controller/metal/rescue.rb:29:in</code>process_action'
    actionpack (3.2.8)
    lib/action_controller/metal/instrumentation.rb:30:in <code>block in
    process_action' activesupport (3.2.8)
    lib/active_support/notifications.rb:123:in</code>block in instrument'
    activesupport (3.2.8)
    lib/active_support/notifications/instrumenter.rb:20:in <code>instrument'
    activesupport (3.2.8) lib/active_support/notifications.rb:123:in
    </code>instrument' actionpack (3.2.8)
    lib/action_controller/metal/instrumentation.rb:29:in <code>process_action'
    actionpack (3.2.8)
    lib/action_controller/metal/params_wrapper.rb:207:in</code>process_action'
    activerecord (3.2.8)
    lib/active_record/railties/controller_runtime.rb:18:in
    <code>process_action' actionpack (3.2.8)
    lib/abstract_controller/base.rb:121:in</code>process' actionpack (3.2.8)
    lib/abstract_controller/rendering.rb:45:in <code>process' actionpack
    (3.2.8) lib/action_controller/metal.rb:203:in</code>dispatch' actionpack
    (3.2.8) lib/action_controller/metal/rack_delegation.rb:14:in
    <code>dispatch' actionpack (3.2.8) lib/action_controller/metal.rb:246:in
    </code>block in action' actionpack (3.2.8)
    lib/action_dispatch/routing/route_set.rb:73:in <code>call' actionpack
    (3.2.8) lib/action_dispatch/routing/route_set.rb:73:in</code>dispatch'
    actionpack (3.2.8) lib/action_dispatch/routing/route_set.rb:36:in
    <code>call' journey (1.0.4) lib/journey/router.rb:68:in</code>block in call'
    journey (1.0.4) lib/journey/router.rb:56:in <code>each' journey (1.0.4)
    lib/journey/router.rb:56:in</code>call' actionpack (3.2.8)
    lib/action_dispatch/routing/route_set.rb:600:in <code>call' actionpack
    (3.2.8) lib/action_dispatch/middleware/best_standards_support.rb:17:in
    </code>call' rack (1.4.1) lib/rack/etag.rb:23:in <code>call' rack (1.4.1)
    lib/rack/conditionalget.rb:35:in</code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/head.rb:14:in <code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/params_parser.rb:21:in</code>call'
    actionpack (3.2.8) lib/action_dispatch/middleware/flash.rb:242:in
    <code>call' rack (1.4.1) lib/rack/session/abstract/id.rb:205:in</code>context'
    rack (1.4.1) lib/rack/session/abstract/id.rb:200:in <code>call' actionpack
    (3.2.8) lib/action_dispatch/middleware/cookies.rb:339:in</code>call'
    activerecord (3.2.8) lib/active_record/query_cache.rb:64:in <code>call'
    activerecord (3.2.8)
    lib/active_record/connection_adapters/abstract/connection_pool.rb:473:in
    </code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/callbacks.rb:28:in <code>block in call'
    activesupport (3.2.8) lib/active_support/callbacks.rb:405:in
    </code><em>run</em>_3479256987463636693_<em>call</em>_4454778504255292268__callbacks'
    activesupport (3.2.8) lib/active_support/callbacks.rb:405:in
    <code>__run_callback' activesupport (3.2.8)
    lib/active_support/callbacks.rb:385:in</code>_run_call_callbacks'
    activesupport (3.2.8) lib/active_support/callbacks.rb:81:in
    <code>run_callbacks' actionpack (3.2.8)
    lib/action_dispatch/middleware/callbacks.rb:27:in</code>call' actionpack
    (3.2.8) lib/action_dispatch/middleware/reloader.rb:65:in <code>call'
    actionpack (3.2.8) lib/action_dispatch/middleware/remote_ip.rb:31:in
    </code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/debug_exceptions.rb:16:in <code>call'
    actionpack (3.2.8)
    lib/action_dispatch/middleware/show_exceptions.rb:56:in</code>call'
    railties (3.2.8) lib/rails/rack/logger.rb:26:in <code>call_app' railties
    (3.2.8) lib/rails/rack/logger.rb:16:in</code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/request_id.rb:22:in <code>call' rack (1.4.1)
    lib/rack/methodoverride.rb:21:in</code>call' rack (1.4.1)
    lib/rack/runtime.rb:17:in <code>call' activesupport (3.2.8)
    lib/active_support/cache/strategy/local_cache.rb:72:in</code>call' rack
    (1.4.1) lib/rack/lock.rb:15:in <code>call' actionpack (3.2.8)
    lib/action_dispatch/middleware/static.rb:62:in</code>call' railties (3.2.8)
    lib/rails/engine.rb:479:in <code>call' railties (3.2.8)
    lib/rails/application.rb:223:in</code>call' rack (1.4.1)
    lib/rack/content_length.rb:14:in <code>call' railties (3.2.8)
    lib/rails/rack/log_tailer.rb:17:in</code>call' rack (1.4.1)
    lib/rack/handler/webrick.rb:59:in <code>service'
    /Users/ogonbat/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:138:in
    </code>service'
    /Users/ogonbat/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/httpserver.rb:94:in
    <code>run' 
    /Users/ogonbat/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/webrick/server.rb:191:in
    </code>block in start_thread'</p>
  </blockquote>
  
  <p>this are the request parameters</p>
  
  <blockquote>
    <p>{"utf8"=>"✓", 
    "authenticity_token"=>"g44p+IPxvdm2ouGAE2u2dV/cCKK8uF6G3XLL4z26zrI=", 
    "page"=>{"title"=>"zfdzfdsf", 
    "contents"=>{"short_description"=>"<p>sdfdsf</p>", 
    "large_description"=>"<p>dsfdsf</p>"}},  "commit"=>"Create"}</p>
  </blockquote>
  
  <p>thank's in advance for your help</p>