Rails instance variable not passing to view with "Render"

Question

Basic rails question..I have the following: a user has many packs and a pack belongs to a category. In the new pack form I want make a select field with the pack's categories. I have the following code :

      def new_pack
       @pack=Pack.new()
       @user= User.find(params[:id])
       @categories = Category.all
      end

      def create
       @pack=Pack.new(pack_params)
       @user= User.find(params[:user_id])
       if @pack.save
        @user.packs << @pack
        flash[:notice]="Thank you!"
        redirect_to(:action=>'attempt_activation', :id=> @pack.id)
       else
        render :action=> "new_pack", :id=>@user.id
       end
      end

And in my view:

      <%= form_for(:pack, :url=>{:controller=> "packs", :action=>'create', :user_id=>                 @user.id}) do |f| %>
       <h5>Registration takes less than 2 minutes.</h5>
       <label>Title<b style="color:red;">*</b>
        <%= f.text_field(:title, :placeholder=>"") %>
       </label>
       <label>Category<b style="color:red;">*</b>
         <%= f.select(:category_id, @categories.map {|s| [s.title, s.id]}, :selected=>  @categories.second) %>
        ...

THE PROBLEM is that if there are errors at the form and and the new_pack action has to be rendered again it throws an error:

       ActionView::Template::Error (undefined method `map' for nil:NilClass):
       </div>
       <div class="large-4 columns">
         <label>Category
           <%= f.select(:category_id, @categories.map {|s| [s.title, s.id]}, :selected=> @pack.category) %>
       </div>

Why is this happening? render is used to render a particular view using the instance variables available in the action but here is not loading again the @categories.

Thank you.

Alexander Kireyev · Accepted Answer · 2014-09-06 23:44:16Z

9

Add @categories = Category.all in create method:

def create
  @pack = Pack.new(pack_params)
  @user = User.find(params[:user_id])
  if @pack.save
    @user.packs << @pack
    flash[:notice] = "Thank you!"
    redirect_to(:action => 'attempt_activation', :id => @pack.id)
  else
    @categories = Category.all
    render :action=> "new_pack", :id => @user.id
  end
end

answered Sep 6, 2014 at 23:44

Alexander Kireyev

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2 Comments

gematzab Over a year ago

Zishe thank you for your answer. This is correct but could you please give me a brief explanation of this solution? When I am rendering the "new_pack" action they get loaded the instance variables of the create action??

Alexander Kireyev Over a year ago

Of course. render action: is the same as render template, you can see it here. It's not possible to somehow trigger other action, only to redirect. And when you just render that template you should have all necessary data, including @categories

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