title: How to pass simple_form hidden_field paramer to create action
body: <p>I am having trouble passing a parameter defined in a hidden_field of a simple_form to a create action.  In our app, a User has many bets through memberships.  Membership columns include bet_id, user_id, accepted:boolean, and against:boolean.  The against column of Membership indicates whether the user is betting against or betting with the bet.  In the view for a particular bet, a user who does not have a membership can choose "Agree" or "Against", which will create a new membership with the appropriate accepted:boolean.  Here are the forms found the the bet show page.</p>
  
  <pre><code>    &lt;%= simple_form_for([@bet, @bet.memberships.build]) do |f| %&gt;
        &lt;%= f.hidden_field :against, against: false %&gt;
        &lt;%= f.button :submit, "Agree!" %&gt;
      &lt;% end %&gt;
  
      &lt;%= simple_form_for([@bet, @bet.memberships.build]) do |f| %&gt;
        &lt;%= f.hidden_field :against, against: true %&gt;
        &lt;%= f.button :submit, "Against!" %&gt;
      &lt;% end %&gt;
  </code></pre>
  
  <p>Here is the attempted create action</p>
  
  <pre><code>def create
    @membership = current_user.memberships.build(bet_id: params[:bet_id], against: params[:against], accepted: :false)
    redirect_to :back
  end
  </code></pre>
  
  <p>This currently just leaves the accepted value as nil.  Any help would really be appreciated! Thanks</p>