I have the same issue as Creating an additional related model with Devise (which has no answer).
I have overridden the devise view for creating a new user and added
You can add the following method to the User model:
user.rb
def with_company
self.companies.build
self
end
And modify the view:
new.html.erb
...
<% form_for [resource_name, resource.with_company], :url => registration_path(resource_name) do |f| %>
...
<% f.fields_for :company do |company_form| %>
...
<% end %>
This way, you'll have the nested form to add one company to the user. To dynamically add multiple companies to the user, check the Railcast #197 by Ryan Bates. Make sure you are passing the pair of resources as an array, otherwide you will get an error like this: "wrong number of arguments (3 for 2)".