I have the following routes defined in my application:
resources :users do
resources :data_sets
end
The form data_sets/new is accessed from the following link:
<%= link_to "New Data Set", new_user_data_set_path(user) %>
The form is defined as such:
<%= form_with model: @data_set, url: [@data_set.author, @data_set] do |form| %>
<!-- form contents... -->
<% end %>
The form gives the following error upon loading:
Showing .../app/views/data_sets/new.html.erb where line #1 raised:
undefined method `data_sets_path' for #<#<Class:0x00007ffd2d1dcf90>:0x00007ffd292a63d0>
The following parameters were passed:
{ "user_id" => "1" }
Similar questions posted here seem to indicate that defining the URL typically solves problems with nested resource forms, but as you can see I already have. What else is going on here?
The form_with helper build the nested url from the array you passed. But in case of new record, @data_set.author returns nil and the form tries to reach data_sets_path which does not exist.
If your form is just for the "new" action you can write:
<%= form_with model: @data_set, url: [:user, @data_set] do |form| %>
If you share the form between "new" and "edit", you can write a condition like that:
<%= form_with model: @data_set, url: [(@data_set.new_record? ? :user : @data_set.author), @data_set] do |form| %>