Use a scope by default on a Rails has_many relationship

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Let's say I have the following classes

class SolarSystem < ActiveRecord::Base
  has_many :planets
end

class Planet < ActiveRecord::Base
  scope :life_supporting, where('distance_from_sun > ?', 5).order('diameter ASC')
end

Planet has a scope life_supporting and SolarSystem has_many :planets. I would like to define my has_many relationship so that when I ask a solar_system for all associated planets, the life_supporting scope is automatically applied. Essentially, I would like solar_system.planets == solar_system.planets.life_supporting.

Requirements

  • I do not want to change scope :life_supporting in Planet to

    default_scope where('distance_from_sun > ?', 5).order('diameter ASC')

  • I'd also like to prevent duplication by not having to add to SolarSystem

    has_many :planets, :conditions => ['distance_from_sun > ?', 5], :order => 'diameter ASC'

Goal

I'd like to have something like

has_many :planets, :with_scope => :life_supporting

Edit: Work Arounds

As @phoet said, it may not be possible to achieve a default scope using ActiveRecord. However, I have found two potential work arounds. Both prevent duplication. The first one, while long, maintains obvious readability and transparency, and the second one is a helper type method who's output is explicit.

class SolarSystem < ActiveRecord::Base
  has_many :planets, :conditions => Planet.life_supporting.where_values,
    :order => Planet.life_supporting.order_values
end

class Planet < ActiveRecord::Base
  scope :life_supporting, where('distance_from_sun > ?', 5).order('diameter ASC')
end

Another solution which is a lot cleaner is to simply add the following method to SolarSystem

def life_supporting_planets
  planets.life_supporting
end

and to use solar_system.life_supporting_planets wherever you'd use solar_system.planets.

Neither answers the question so I just put them here as work arounds should anyone else encounter this situation.

ruby-on-rails-3 has-many activerecord
3 Answers

In Rails 5, the following code works fine... 

  class Order 
    scope :paid, -> { where status: %w[paid refunded] }
  end 

  class Store 
    has_many :paid_orders, -> { paid }, class_name: 'Order'
  end
user_738900
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