Nested Resources w/ Rails 5.1 form_with

Question

Per this pull request I can see that an array should be passed to form_with's model param. However, when I supply the following:

<%= form_with(model: [@trip, @activity], local: true) do |f| %>   ... <% end %> 

Rails will return - ActionView::Template::Error (undefined method activity_path' for #<#<Class:0x007f80231e3070>:0x007f8023010dd8>):

My routes file looks like:

  resources :trips do     resources :activities   end 

The output of rake routes looks like -

     trip_activities GET    /trips/:trip_id/activities(.:format)          activities#index                      POST   /trips/:trip_id/activities(.:format)          activities#create    new_trip_activity GET    /trips/:trip_id/activities/new(.:format)      activities#new   edit_trip_activity GET    /trips/:trip_id/activities/:id/edit(.:format) activities#edit        trip_activity GET    /trips/:trip_id/activities/:id(.:format)      activities#show                      PATCH  /trips/:trip_id/activities/:id(.:format)      activities#update                      PUT    /trips/:trip_id/activities/:id(.:format)      activities#update                      DELETE /trips/:trip_id/activities/:id(.:format)      activities#destroy                trips GET    /trips(.:format)                              trips#index                      POST   /trips(.:format)                              trips#create             new_trip GET    /trips/new(.:format)                          trips#new            edit_trip GET    /trips/:id/edit(.:format)                     trips#edit                 trip GET    /trips/:id(.:format)                          trips#show                      PATCH  /trips/:id(.:format)                          trips#update                      PUT    /trips/:id(.:format)                          trips#update                      DELETE /trips/:id(.:format)                          trips#destroy 

And my activities_controller.rb -

  before_action :set_activity, only: %i[show update edit destroy]    def edit; end    def update     dates = calculate_datetimes(params[:date_range])     @activity.assign_attributes(name: params[:name],                                 summary: params[:summary],                                 start_datetime: dates[0],                                 end_datetime: dates[1])     if @activity.save       flash[:success] = 'Activity successfully updated'       redirect_to(@trip)     else       set_humanized_daterange       render :edit     end   end    private     def set_activity     @activity = Activity.find(params[:id])   end 

tl;dr - how should I setup my form_with for a nested resource, and why is this form thinking I want to use the activity_path? Ideally I'd like to move this form into a partial and use the same form for both my #new and #edit actions.

Answer 1

Try specifying the model and url separately:

form_with(model: @activity, url: [@trip, @activity]) 

According the docs the the values for url are "Akin to values passed to url_for or link_to" so using an array should work.

This also works with shallow nesting since the array is compacted.