Formtastic checkboxes not getting checked when editing resource, when using MongoMapper

Question

With the following Store and Service models, managed with MongoMapper:

class Store
  include MongoMapper::Document         
  key :service_ids, Array, :typecast => 'ObjectId'
  many :services, :in => :service_ids
end

class Service
  include MongoMapper::Document         
  key :name, String  
  many :stores, :foreign_key => :service_ids  
end

I have this form, done with Formtastic:

<%= semantic_form_for @store, :url => admin_store_path(@store), :method => :put do |form| %>
  <%= form.input :service_ids, :label => "Select Store Services", 
                               :as => :check_boxes, 
                               :collection => Service.all %>
<% end -%>

The controller uses Inherited Resources, and the edit action is implicit.

When editing a @store with services already associated with it, the checkboxes for the latter don't show as checked.

Formtastic's README warns it doesn't support MongoMapper officially, but it also says people have been using both together successfully, and I've seen some examples of this online.

I suspect Inherited Resources also doesn't support it, from what I've seen from Devise + Simple Form, both from the same authors and which don't support MM. They're working towards using an ORM adapter in their gems, but it isn't ready yet AFAIK.

And I've had problems with it already, I'm overriding the update action to get it to work:

  def update
    store = Store.find(params[:id])    
    if store.update_attributes!(params[:store])

      flash[:notice] = 'Store was successfully updated.'
      redirect_to admin_store_path(store)
    else
      redirect_to new_store_path
    end
  end  

Does anybody know where the conflict with MM is, either in Formtastic or IR, and a hack just to get these checkboxes checking?

Answer 1

Most likely a Formtastic issue. It looks like the problem is here: https://github.com/justinfrench/formtastic/blob/master/lib/formtastic/inputs/check_boxes_input.rb#L122

Formtastic calls @store.service_ids to find the selected boxes. Service_ids returns an array of ObjectId's, but Formtastic was expecting an array of Store objects. If we follow Formtastic's code we'll see it tries a couple methods to find out how to get the "value" out of those ObjectId's and will eventually settle on "to_s" (see https://github.com/justinfrench/formtastic/blob/master/lib/formtastic/form_builder.rb#L20). Unfortunately, the to_s of an ObjectId is not the same as the id of your Store objects.

A hack that might make it work is to add an "id" method to ObjectId that returns self (Formtastic looks for id before it looks for to_s). A more appropriate patch would be to override this method https://github.com/justinfrench/formtastic/blob/master/lib/formtastic/inputs/base.rb#L104 to properly introspect MongoMapper associations, so that you could write form.input :services and it would turn that into an input with name of "service_ids" while still using the services method of your object. With that change it would still properly call @store.services and find the same kind of objects as Store.all and just work.

If you want to go that route, Store.associations[:services] should get you MongoMapper's definition of the association which you can introspect (see https://github.com/jnunemaker/mongomapper/blob/master/lib/mongo_mapper/plugins/associations/base.rb) but note that associations have been refactored a bit since the 0.8.6 gem, they're now in the separate classes BelongsToAssociation, OneAssociation, and ManyAssociation that each inherit from Associations::Base.

So, it doesn't seem like there's a simple fix. The other option is to generate your checkboxes by hand.

(Aside: I'm a little confused by your update method because I'd expect IR to do exactly what you've written internally, but if you had to write it that way to get it to work, so it is...)