Unpermitted parameters on belong_to association - ruby-on-rails

Question

I have an association as follows:
class Membership < ApplicationRecord
belongs_to :user
end
and
class User < ApplicationRecord
has_many :memberships
end
Now I have a form to create a new membership. Within this form I also want to input new user information. I am using SimpleForm. My basic structure is as follows (using HAML not erb files):
= simple_form_for #membership do |f|
...
= simple_fields_for #user do |uf|
.field= uf.input :firstname, label: 'First Name', required: true
...
= f.button :submit, 'Submit'
#user here is an instance variable set in the new action on the Memberships controller (#user = User.new). I would like to keep it this way so I can use SimpleForm's inference on user attributes (i.e., uf.input :firstname maps to the firstname attribute on the User model)
Now given this background, when I hit submit the goal is to create a new membership and a new user associated to that membership. How can I permit parameters for the single associated user?
At the moment I have:
# Never trust parameters from the scary internet, only allow the white list through.
def membership_params
params.require(:membership).permit(users_attributes: [:id, :firstname] )
end
Here is the request:
Started POST "/memberships" for ::1 at 2018-10-15 15:08:42 -0600
Processing by MembershipsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"omitted==", "membership"=>{"user"=>{"firstname"=>""}}, "commit"=>"Submit"}
Unpermitted parameter: :user
Unpermitted parameter: :user
Unpermitted parameter: :user
##################### {}
No template found for MembershipsController#create, rendering head :no_content
Completed 204 No Content in 264ms (ActiveRecord: 0.0ms)
I have no template rendering on purpose for now.
Given this parameter structure:
"membership"=>{"user"=>{"firstname"=>""}}
I have also tried the following for permitted parameters:
params.require(:membership).permit(user_attributes: [:id, :firstname] )
params.require(:membership).permit(user: [:id, :firstname] )
Notice I the ################ {}. This is a manual puts I have in the create action. puts '################ ' + membership_params.to_json. As you can see it yields nothing. Also why do I get the 'Unpermitted parameters' logged three times?
UPDATE 1 controller code:
class MembershipsController < ApplicationController
load_and_authorize_resource
# GET
def new
#membership_plans = Plan.active.sort_by { |plan| plan.sequence }
#user = #membership.build_user
end
# POST
def create
debug_puts(membership_params.to_json)
end
private
# Never trust parameters from the scary internet, only allow the white list through.
def membership_params
params.require(:membership).permit(user_attributes: [:id, :firstname, :lastname] )
end
end
UPDATE 2
I don't deem this as an acceptable answer (which is why I'm not formally "answering" my question), but what I have decided to do is invert my form. The relationship is still the same among Memberships and Users, but the parent form is for a User:
= simple_form_for #user do |f|
...
= f.simple_fields_for :memberships_attributes do |mf|
...
This means I put accepts_nested_attributes_for :membership on the User model (a has_many association with memberships) and all the rendering and param permitting is done within the Users Controller
# new action in users_controller.rb
def new
#membership_plans = Plan.active.sort_by { |plan| plan.sequence }
#user = User.new
#user.build_membership
end
# Never trust parameters from the scary internet, only allow the white list through.
def user_params
params.require(:user).permit(memberships_attributes: [:id, :field1, :field2] )
end

Answer 1

You need to build the user for membership in the new action of memberships_controller.
def new
#membership = Membership.new
#user = #membership.build_user
end
and make sure you have user_attributes not users_attributes in the membership_params
params.require(:membership).permit(user_attributes: [:id, :firstname] )
Update:
There is one more important piece of code which need to be fixed.
This
= simple_fields_for #user do |uf|
should be
= f.simple_fields_for #user do |uf|