moebooru/db/migrate/005_create_forum_post.rb

class CreateForumPost < ActiveRecord::Migration[5.1]
  def self.up
    execute(<<-EOS)
      CREATE TABLE forum_posts (
        id SERIAL PRIMARY KEY,
        created_at TIMESTAMP NOT NULL,
        updated_at TIMESTAMP NOT NULL,
        title TEXT NOT NULL,
        body TEXT NOT NULL,
        creator_id INTEGER NOT NULL REFERENCES users ON DELETE CASCADE,
        parent_id INTEGER REFERENCES forum_posts ON DELETE CASCADE
      )
    EOS
  end

  def self.down
    execute("DROP TABLE forum_posts")
  end
end