Question

So i have the following code:

def new 
    @all_areas = Area.all
    @area = Area.new
end

The reason i am passing in all_areas is it’s required for a drop down box in the form, Using mongoid and an Area can be recursively embedded in another Area.

My form has the following code:

 <% if @all_areas %>
        <%= f.label :parent_area %>
        <%= f.collection_select(:parent_area, @all_areas, :_id, :name, prompt: "Select a Parent...") %>
    <% end %>

However when i submit ‘invalid values, i.e blank name, the ‘new’ page does not render the select box to select a parent.

What is going on here? Is this a bug?

My create action is pretty simple, if it fails validation i just do the following:

else
     render 'new'

Why is @all_areas not passed to the view the second time? i have actually fixed it by changing the code in my create action to the following:

else
    @all_areas = Area.all
    render 'new'

But this is quite surprising, unless i am missing something?

Answer 1

It’s not a bug. The reason for the behaviour is that the create action is actually quite separate from the new action, so the instance variables you assigned in new don’t get carried over. render 'new' only renders the view called “new”, it doesn’t actually call the new action.

new happens when you issue a GET request to /areas/new. create happens when you POST to /areas. Because they’re separate requests, the server doesn’t remember any state – in fact, you could call create without ever calling new (say if you used curl from the command line).

Basically, your approach is correct, you need to set the @all_areas instance variable in both actions. You might want to extract it out into a separate private method to avoid the duplication.