Ruby on Rails - Polymorphic Association with Categories - ruby-on-rails

Question

I'm currently trying to implement a Category model to my application. I'm trying to design it in a way that Users can have many Categories, and so can Groups.
The problem I'm running into is that I also want to be able to just have a normal list of Categories without them being assigned to any User or Group.
I was referencing rubyonrails.org/association_basics.
class CreateCategories < ActiveRecord::Migration[5.0]
def change
create_table :categories do |t|
t.string :name
t.text :description
t.references :categorizable, polymorphic: true, index: true
t.timestamps
end
end
end
class Category < ApplicationRecord
belongs_to :categorizable, :polymorphic => true
end
class User < ApplicationRecord
has_many :categories, :as => :categorizable
end
class Group< ApplicationRecord
has_many :categories, :as => :categorizable
end
I'm trying to create a new Category through rails c, but whenever I try to save, it rolls back my transaction probably because I'm missing some condition.
Category(id: integer, name: string, description: text, created_at: datetime, updated_at: datetime)
Category.create( :id => 1, :name => 'Category_1', :description => '' )
begin transaction
rollback transaction
I also feel like there is a better way to create a new Category, as I shouldn't be setting the id manually.
Thanks for your help.

Answer 1

In rails 5, whenever you define a belongs_to association, it is required to have the associated record present by default. You would see this when you look at the errors after trying to create the category object
category = Category.create(:name => 'Category_1', :description => '' )
category.errors.full_messages.to_sentence
If you want to be able to save a record without the belongs_to association, you would have to specify it explicitly
class Category < ApplicationRecord
belongs_to :categorizable, polymorphic: true, required: false
end

Answer 2

If you try to create a new category and see the error is that there needs to exists a categorizable record in order for the category to be created, an easy way to do it is to put the new object itself as the categorizable one and it should do the trick.
$ category = Category.new
=> #<Category id: nil, name: nil, description: nil, categorizable_type: nil, categorizable_id: nil, created_at: nil, updated_at: nil>
$ category.save
(0.1ms) begin transaction
(0.1ms) rollback transaction
=> false
$ category.errors.full_messages
=> ["Categorizable must exist"]
$ category = Category.new(categorizable: category)
=> #<Category id: nil, name: nil, description: nil, categorizable_type: "Category", categorizable_id: nil, created_at: nil, updated_at: nil>
$ category.save
(0.1ms) begin transaction
SQL (1.3ms) INSERT INTO "categories" ("categorizable_type", "created_at", "updated_at") VALUES (?, ?, ?) [["categorizable_type", "Category"], ["created_at", 2017-01-15 00:08:55 UTC], ["updated_at", 2017-01-15 00:08:55 UTC]]
(0.7ms) commit transaction
=> true

Answer 3

This should help, Rails Cast on Polymorphic
https://www.youtube.com/watch?v=6l9EAuev16k
You can create polymorphic records with this...
`#category = #categorizable.User.new`
`#category = #categorizable.Group.new`
So you do not need the id.