Dumb Things With Postgres

01.rb

class Article < ActiveRecord::Base
  # all the other logic

  def associated_articles
    Article.where.not(id: id).where('tags && ARRAY[?]', tags)
  end
end

02.rb

class ChangeXIdColumn < ActiveRecord::Migration
  def up
    remove_index :products, :product_category_id
    change_column :products, :product_category_id, 'integer[] USING ARRAY[product_category_id]::INTEGER[]', array: true, null: false, default: []
    rename_column :products, :product_category_id, :product_category_ids
    add_index :products, :product_category_ids, using: 'gin'
  end

  def down
    raise ActiveRecord::IrreversibleMigration
  end
end

03.rb

change_column :products, :product_category_id, 'integer[] USING ARRAY[product_category_id]::INTEGER[]', array: true, null: false, default: []

04.rb

add_index :products, :product_category_ids, using: 'gin'

05.rb

def product_categories
  ProductCategories.where(id: product_category_ids)
end