title: expected Hash (got Array) for param 'samples'
body: <p>I have been following Railscasts episodes of Nested forms and complex forms. During the time of creating multiple model in a single form I was able to edit, update, delete and create records for sample models that were nested in the Batch model. </p>
  
  <p>I have been breaking my head from a long time and tried searching around as well but could not get any right solution for solving this problem.</p>
  
  <p>my development log file gives me the following error.</p>
  
  <p>ERROR MESSAGE:</p>
  
  <pre><code>Status: 500 Internal Server Error
    expected Hash (got Array) for param `samples'
  </code></pre>
  
  <p>in my controller I have the update action like this </p>
  
  <pre><code>def update
       @batch = Batch.find(params[:id])
  
       respond_to do |format|
         if @batch.update_attributes(params[:batch])
           flash[:notice] = 'Successfully updated Batch.'
           format.html { redirect_to(@batch) }
           format.xml  { head :ok }
         else
           format.html { render :action =&gt; "edit" }
           format.xml  { render :xml =&gt; @batch.errors, :status =&gt; :unprocessable_entity }
         end
       end
     end
  </code></pre>
  
  <p>my view is something like this:</p>
  
  <pre><code>&lt;%= form_for @batch do |f| %&gt;
  ......
  &lt;%= f.fields_for :samples do |s_form| %&gt;
  .... s_form things
  &lt;% end %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>my model contains the same stuff :</p>
  
  <pre><code>has_many :samples, :dependent =&gt; :destroy
  
    accepts_nested_attributes_for :samples, :reject_if =&gt; lambda { |a| a[:content].blank? }, :allow_destroy =&gt; true
  </code></pre>
  
  <p>All suggestions are appreciated.</p>