rails includes query loading entire data for included models

Question

I have a rails application where I have following models.

BookingHotel
    has_many :hotel_picture_partners, through: :hotel_pictures
    has_many :booking_hotel_partner_details, dependent: :destroy

BookingHotelPartnerDetail
    belongs_to :booking_hotel

HotelPicturePartner
    belongs_to :hotel_picture, dependent: :destroy

I have a query as follows

@booking_hotel_partner_details = BookingHotelPartnerDetail.unscoped.select(:id, :booking_hotel_id, :partner_booking_hotel_id).includes(booking_hotel: :hotel_picture_partners)

This puts memory under pressure as it loads all data for included models.

Is there a way I can only load selective fields from booking_hotels & hotel_picture_partners tables ?

Also I want to get an activerecord array as response.

Possible duplicate of [Rails 3 - select with Include?](http://stackoverflow.com/questions/4047833/rails-3-select-with-include) — Hasmukh Rathod, Aug 17 '16 at 07:47

Andrey Saleba · Accepted Answer · 2016-08-17T07:45:41.187

1

pluck method loads only attributes, without loading whole models. check it: http://apidock.com/rails/ActiveRecord/Calculations/pluck.

Try to rewrite it like this: BookingHotelPartnerDetail.unscoped.select('booking_hotels.id as bh_id', 'hotel_picture_partners.id as hpp_id').joins(booking_hotel: :hotel_picture_partners)

edited Aug 17 '16 at 07:45

answered Aug 17 '16 at 07:17

Andrey Saleba

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I want to load included models but pluck will give me an array – RamanSM Aug 17 '16 at 07:30
It seems to be correct Andrey. This will not load all associated records in memory right ? – RamanSM Aug 17 '16 at 07:58
Raman M, it won't eager load it, right, you can check the SQL query generated by this AR query in Rails logs. – Andrey Saleba Aug 17 '16 at 08:11

score 0 · Answer 2 · answered Nov 24 '22 at 09:52

Your project is probably already pretty far along, but for anyone else wanting this behaviour I've released a patch that filters columns if you have a .select(...) along with .includes(...) or .eager_load(...). It's now included in a data-related gem I maintain, The Brick.

It works by overriding ActiveRecord::Associations::JoinDependency.apply_column_aliases() like this.

In order to enable this selective behaviour, add the special column name :_brick_eager_load as the first entry in your .select(...), which turns on the filtering of columns while the aliases are being built out. Here's an example based on your code:

@booking_hotel_partner_details =
  BookingHotelPartnerDetail.unscoped
                           .includes(booking_hotel: :hotel_picture_partners)
                           .select(:_brick_eager_load, :id, :partner_booking_hotel_id, 'booking_hotel.name', 'hotel_picture_partners.notes')

Feel free to add myraid additional columns from any table as strings in the same way as the last two sample items I put into the .select(...).

Because foreign keys are essential to have everything be properly associated, they are automatically added, so you do not need to include :booking_hotel_id in your select list.

Hope it can save you both query time and some RAM!

rails includes query loading entire data for included models

2 Answers2