Rails4 model ignores parent_id on 'create' action - ruby-on-rails

Question

I have Subcategories which belong to Categories. My app saves (build) all my Subcategories under Subcategory with id = 1, even though my code seems to be ok and it is not supposed to do that:
Subcategories controller:
def create
#category = Category.find_by(params[:id])
#subcategory = #category.subcategories.build(subcategory_params)
if #subcategory.save
flash[:success] = "added subcategory"
redirect_to admin_categories_url
else
render :new
end
end
...
private
def subcategory_params
params.require(:subcategory).permit(:name, :category_id)
end
Subcategory.rb
class Subcategory < ActiveRecord::Base
belongs_to :category
has_many :products
validates :name, presence: true
validates :category_id, presence: true
end
Form:
<h3>Add a subcategory</h3>
<%= form_for [#category, #subcategory] do |f| %>
<%= f.text_field :name, placeholder: "Name" %>
<%= f.submit "Add a subcategory" %>
<% end %>
router:
resources :categories do
resources :subcategories
end
URL:
Adding a new subcategory to category with id = 3
http://localhost:3000/categories/3/subcategories/new
Logs:
Started POST "/categories/1/subcategories" for 127.0.0.1 at 2014-04-16 16:04:47 +0400
Processing by SubcategoriesController#create as HTML
Parameters: {"utf8"=>"✓", authenticity_token"=>"74U3VyAN6NqEjhkuHGNHnPda/yzpc+dIcn2xBJ6Zi2A=", "subcategory"=>{"name"=>"A name"}, "commit"=>"Add subcategory", "category_id"=>"1"}
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1 [["id", 1]]
Category Load (0.2ms) SELECT "categories".* FROM "categories" WHERE "categories"."id" = $1 LIMIT 1 [["id", 1]]
(0.1ms) BEGIN
SQL (0.2ms) INSERT INTO "subcategories" ("category_id", "created_at", "name", "updated_at") VALUES ($1, $2, $3, $4) RETURNING "id" [["category_id", 1], ["created_at", "2014-04-16 12:04:47.151729"], ["name", "A name"], ["updated_at", "2014-04-16 12:04:47.151729"]]
(0.8ms) COMMIT
Id is 1
What can be the problem here?
Update
When doing
#category = Category.find_by(params[:category_id])
this error comes up:
ERROR: argument of WHERE must be type boolean, not type integer
LINE 1: SELECT "categories".* FROM "categories" WHERE (1) LIMIT 1
If doing
#category = Category.find(params[:category_id])
problem presists

Answer 1

In your create action you are picking up the id of the subcategory, not the category. Change it to:
def create
#category = Category.find(params[:category_id])
...
The same change to setting #category needs to be made in the new method too so that category_id comes back as 3 in the params from the view. Of course this duplication can be also DRYed up using a helper method in the controller.
To see the difference in the id, you can use rake routes and you should see something like:
new_category_subcategory GET /categories/:category_id/subcategories/new subcategories#new
This shows you that it expects the parameter category_id for the id of the category.

Answer 2

Look at your parameters it consist category_id not id
Parameters: {"utf8"=>"✓", authenticity_token"=>"74U3VyAN6NqEjhkuHGNHnPda/yzpc+dIcn2xBJ6Zi2A=", "subcategory"=>{"name"=>"A name"}, "commit"=>"Add subcategory", "category_id"=>"1"}
#=> "category_id"=>"1"
Category.find_by(category_id: params[:category_id])
So you need to do
def create
#category = Category.find_by(category_id: params[:category_id])
#subcategory = #category.subcategories.build(subcategory_params)
if #subcategory.save
flash[:success] = "added subcategory"
redirect_to admin_categories_url
else
render :new
end
end