CODEWITHSUNDEEP
ruby-on-railsrubyrails-activerecord
CV-Gate
CV-Gate

Reputation: 1170

Rails Active Record query including delegated attributes

Is it possible to make a query like this? (Pseudo-code)

u=User.includes(all_delegated_attributes_from_relationships).all

How?

Further explanation:

class User<ActiveRecord::Base
  has_one :car
  delegate :wheel, :brake, :motor, to: :car, prefix: true
end

and then:

u=User.includes(delegated_car_parts).all
#<user id: 1, car_id: 1, name: "John", car_wheel: "foo", car_motor: "bar", car_brake: false>

I know that this can sound a little odd but I have to add a feature to an old app to export all delegated attributes from a model to CSV and this model has 14 relationships and 300 delegations... I just learnt Demeter's law when I made this app...

Upvotes: 1

Views: 4051

Answers (2)

BroiSatse
BroiSatse

Reputation: 44685

There is no build-in method to do this. You could try sth like:

class User < ActiveRecord::Base
  has_one :car

  DelegatedCarMethods  = [:wheel, :brake, :motor]
  delegate *DelegatedCarMethods, to: :car, prefix: true

  scope :with_car_delagations, lambda do
    select_array = ["#{table_name}.*"]
    select_array += DelegateCarMethods.map {|method| "#{Car.table_name}.#{method} AS car_#{method}"}
    select(select_array.join(', ')).joins(:car)        
  end
end

But it isn't extremely pretty. Why do you need this? Calling user.wheel or user.motor doesn't feel right.

Upvotes: 2

John Naegle
John Naegle

Reputation: 8247

Assuming wheel, break and motor are relationships on car, you can do this:

User.includes(:car => [:wheel, :brake, :motor]).all

Upvotes: 3

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