no association in params for create ...

PoolsController.rb

class PoolsController < ApplicationController

  def index
    @event = Event.find params[:event_id]
    @pools = @event.pools
  end

  def new
    type = nil
    type = params[:type] if ["date", "text"].include?params[:type]
    @event = Event.find params[:event_id]

    @new_pool = @event.pools.build(:user => current_user)

    if type == "date"
      #@yesno_pool = YesNoDatePool.new(:user => current_user, :event => @event)
      #@multi_pool = MultipleDatePool.new(:user => current_user, :event => @event)
      @new_pool.type = "YesNoDatePoll"

      foo = 0
    else
    end


  end

  def create
    @event = Event.find params[:event_id]
    @pool = @event.pools.build params[:pool]

    if @pool.save
      flash[:notice] = "Pool created"
      # redirect
    else
      flash[:error] = "Pool not created"
      render :action => 'new'
    end

  end
end

poolsnews.html.erb

<div id="sondage-creation">

  <h2 class="title">Nouveau sondage (nommer)</h2>

  <%#
  new_event_pool GET    (/:locale)/events/:event_id/pools/new(.:format)
  {:locale=>/en|fr/, :action=>"new", :controller=>"pools"}
    %>
  <%# form_for(:project, @project, :url => {:controller => "projects",:action => "update"}) %>
  <%#= form_for([@event, @new_pool], :as => :poll , :url => {:controller => "pools", :action => "create"}, :validate => true) do |f| %>
  <%= form_for [@event, @new_pool], :validate => true do |f| %>
      <%= f.hidden_field :user_id, @new_pool.user_id %>
      <%= f.hidden_field :event_id, @new_pool.event_id %>
      <fieldset>
        <div class="left">
          <h3><%= t '.question' %></h3>
          <%= f.text_area :question %>
          <h3><%= t '.message' %></h3>
          <%= f.text_area :message %>
        </div>

        <!--<div class="right">-->
          <!--<h3><%#= t '.test_one_date' %> <input name="questionType" value="simple" type="radio"></h3>-->
          <!--<ul>-->
            <!--<li><input name="" value="oui" type="text"></li>-->
            <!--<li><input name="" value="non" type="text"></li>-->
          <!--</ul>-->
          <!--<h3><%#= t '.test_multiple_date' %> <input name="questionType" value="multiple" type="radio"></h3>-->
          <!--<ul>-->
            <!--<li><input name="" type="text"></li>-->
            <!--<li><input name="" type="text"></li>-->
            <!--<li><input name="" type="text"></li>-->
            <!--<li><input name="" type="text"></li>-->
            <!--<li><input name="" type="text"></li>-->
          <!--</ul>-->
        <!--</div>-->

      </fieldset>

      <div class="submit">
        <%= f.submit t '.validate' %>
       <input value="Valider le sondage" type="submit"><br>
        <a href="" class="button"><span>Illustre ton songage</span></a>
      </div>


  <% end %>

</div>