Nested form params not working due to strong parameters - ruby-on-rails-4

Question

I have a model Declaration which has many Costs:
class Declaration < ActiveRecord::Base
has_many :costs
accepts_nested_attributes_for :costs
end
class Cost < ActiveRecord::Base
belongs_to :declaration
end
I want a form where I have 10 cost lines for a declaration, so in the Declaration controller I have the follwing, with the permit params for strong parameters:
def new
#declaration = Declaration.new
#costs = Array.new(10) { #declaration.costs.build }
end
def create
#declaration = Declaration.new(declaration_params)
if #declaration.save
redirect_to user_declarations_path, notice: I18n.t('.declaration.message_create')
else
render action: "new"
end
end
private
def declaration_params
params.require(:declaration).permit(:approval_date, :submit_date, :status, :user_id, :declaration_number,
costs_attributes: [:id, :description, :amount_foreign, :rate, :amount, :cost_date, :projectuser_id])
end
And there is the form of course, so when I submit the form I see this in the log:
Started POST "/users/3/declarations" for 127.0.0.1 at 2013-09-05 19:12:38 +0200
Processing by DeclarationsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"mhaznOuBy/zj7LA/nIpDTy7X2u5UrR+0jleJsFid/JU=", "declaration"=>{"user_id"=>"3", "cost"=>{"cost_date(3i)"=>"", "cost_date(2i)"=>"", "cost_date(1i)"=>"", "projectuser_id"=>"", "description"=>"", "amount_foreign"=>"", "rate"=>"", "amount"=>""}}, "commit"=>"Opslaan", "user_id"=>"3"}
User Load (0.7ms) SELECT "users".* FROM "users" WHERE "users"."id" = 3 ORDER BY "users"."id" ASC LIMIT 1
Unpermitted parameters: cost
So why do I get an unpermitted parameter cost??
Update: declaration form added below:
- if can? :create, Declaration
= form_for [current_user, #declaration] do |f|
= f.hidden_field :user_id, value: current_user.id
.row
.page-header
.span7
%h1.title
%i{ class: "icon-coffee icon-large" }
= I18n.t('.declaration.add_title')
.span5
.action
- if can? :create, Declaration
= link_to I18n.t('.general.cancel'), user_declarations_path(current_user), class: 'btn'
= f.submit(class: 'btn', value: I18n.t('.general.save'))
.row
.span12
= render "layouts/error_messages", target: #declaration
.row
.span12
= render "form", f: f
And the rendered form:
.row
.span12
%table.table.table-striped#declarations
%thead
%tr
%th= I18n.t('.cost.cost_date')
%th= I18n.t('.cost.project')
%th= I18n.t('.cost.description')
%th= I18n.t('.cost.amount_foreign')
%th= I18n.t('.cost.rate')
%th= I18n.t('.cost.amount')
%tbody
- #costs.each do |cost|
= f.fields_for cost, html: { class: "form-inline"} do |c|
%tr
%td{ "data-title" => "#{I18n.t('.cost.cost_date')}" }= c.date_select :cost_date, { include_blank: true, default: nil }
%td{ "data-title" => "#{I18n.t('.cost.project')}" }= c.collection_select :projectuser_id, #projectusers, :id, :full_name, include_blank: true
%td{ "data-title" => "#{I18n.t('.cost.description')}" }= c.text_field :description, class: "input-large"
%td{ "data-title" => "#{I18n.t('.cost.amount_foreign')}" }= c.text_field :amount_foreign, class: "input-small", type: :number, step: "any"
%td{ "data-title" => "#{I18n.t('.cost.rate')}" }= c.text_field :rate, class: "input-small", type: :number, step: "any"
%td{ "data-title" => "#{I18n.t('.cost.amount')}" }= c.text_field :amount, class: "input-small", type: :number, step: "any"
With permit! I get this error message:
Started POST "/users/3/declarations" for 127.0.0.1 at 2013-09-09 09:29:44 +0200
Processing by DeclarationsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"jQwy7psQwixneWF8DezrR/Wo5VKU/dpfz+sosiatm9c=", "declaration"=>{"user_id"=>"3", "cost"=>{"cost_date(3i)"=>"", "cost_date(2i)"=>"", "cost_date(1i)"=>"", "projectuser_id"=>"", "description"=>"", "amount_foreign"=>"", "rate"=>"", "amount"=>""}}, "commit"=>"Opslaan", "user_id"=>"3"}
User Load (0.6ms) SELECT "users".* FROM "users" WHERE "users"."id" = 3 ORDER BY "users"."id" ASC LIMIT 1
Completed 500 Internal Server Error in 6ms
ArgumentError - wrong number of arguments (6 for 0):
app/controllers/declarations_controller.rb:70:in `declaration_params'
app/controllers/declarations_controller.rb:21:in `create'

Answer 1

First impression is you are returning three cost_date parameters. I think this needs to be returned as an array. Your params would then be:
def declaration_params
params.require(:declaration).permit(:approval_date, :submit_date, :status, :user_id, :declaration_number,
costs_attributes: [:id, :description, :amount_foreign, :rate, :amount, :projectuser_id, :cost_date =>[]])
end
Then instead of your web server getting back:
... "cost"=>{"cost_date(3i)"=>"", "cost_date(2i)"=>"", "cost_date(1i)"=>"",...
it should get:
"cost"=>{"cost_date"=>["","",""],...
though without seeing the form I don't know if this is what you are trying to achieve.

Answer 2

It seems that changing this:
- #costs.each do |cost|
= f.fields_for cost, html: { class: "form-inline"} do |c|
to this:
= f.fields_for(:costs) do |c|
Does the trick, because now all costs records are being saved. In the controller I have now this:
#declaration = Declaration.new
10.times do |n|
#declaration.costs.build
end
The only issue I have now left is that it saves empty cost records.