I want to be able to store values even if the related column is empty in rails

Question

What we want to achieve

I'm doing the association in Rails, I'm associating the Schedule table with the PostItem table, and I'm associating the PostItem with belongs_to in the Schedule table, even if the PostItem_id associated with it in the Schedule table is empty. I would like to be able to save the file. In other words, I don't want to make the association every time; I always need the PostItem_id when I make the association within migration. Is there any way to allow saving even if the associated parent is empty?

Code

Migration File

class CreateSchedules < ActiveRecord::Migration[6.0]
  def change
    create_table :schedules do |t|
      t.string :name
      t.string :color
      t.integer :start
      t.integer :end
      t.boolean :timed
      t.boolean :long_time
      t.integer :postItem_id #　I want to save the file even if it is empty.

      t.timestamps
    end
  end
end

Schedule Model

class Schedule < ApplicationRecord
  belongs_to :post_item
    validates :start, presence: true
    validates :end, presence: true
    # validates :postItem_id, allow_nill: true, allow_blank: true
end

postItem model

class PostItem < ApplicationRecord
  belongs_to :post
  has_many :schedules
end

Answer 1

After Rails 5 belongs_to associations are required by default. If you want it to be optional, you can add optional: true.

belongs_to :post_item, optional: true

You can also change this behaviour per model by doing:

self.belongs_to_required_by_default = false

https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#active-record-belongs-to-required-by-default-option