Rails 3 app model how ensure only one boolean field set to true at a time

Question

I have a Logo model that has fields of name:string, default:boolean. I want the true value to be unique, so that only one item in the database can be set to true at once. How do

Answer 1

I also recommend falsifying all your records then making them true.

add_column :users, :name ,:boolean, default: false

Answer 2

class Model < ApplicationRecord
  before_save :ensure_single_default, if: :is_default?

  private

  def ensure_single_default
    self.class.update_all(is_default: false)
  end
end

You don't need to check the id because this callback happens before the truthy one is saved.

Answer 3

I think it's good to check if the one you save is true before you falsify others. Otherwise you falsify everyone when you save a record that isn't active.

def falsify_all_others
    if self.default
        self.class.where('id != ? and default', self.id).update_all("default = 'false'")
    end
end

Answer 4

This code is stolen from previous answer and slightly simplified:

def falsify_all_others
  Item.where('id != ?', self.id).update_all("default = 'false'")
end

You can use this method in before_save callback in your model.

Actually, it is better to "falsify" only records which values are 'true', like this:

Item.where('id != ? and default', self.id).update_all("default = 'false'")

UPDATE: to keep code DRY, use self.class instead of Item:

self.class.where('id != ? and default', self.id).update_all("default = 'false'")

Answer 5

If you're coming here in a more recent time and are using Rails 6, this should be covered on the database level as well as the model level:

db level:

add_index :items, :default, unique: true, where: '(default IS TRUE)', algorithm: :concurrently

model level:

class Item < ApplicationRecord
  scope :default, -> { where(default: true) }

  validates :default, uniqueness: { conditions: -> { default } }
end

Answer 6

if you want this to work for creating and updating (rails v4) make note of this tidbit from rails guides

after_save runs both on create and update, but always after the more specific callbacks after_create and after_update, no matter the order in which the macro calls were executed.