Like you know from "How to tell ActiveRecord how to preload associations (either JOINs or separate queries)", you can tell ActiveRecord explicitly if it should use a LEFT OUTER JOIN or a separate query to preload associations.

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Here is some special case, where a simple includes is not possible. For the diagram below we want to sort the rides by the translated name of the departure_place and the arrival_place:

Here is the list of features we want to achieve:

• Paginated (using will_paginate Show archive.org snapshot )
• Ordered by translated name of departure_place and arrival_place
• No N+1 queries

This is normally straightforward, but as we are referencing the table we want to order on twice some adjustments need to be made.

Ride
.joins('inner join places as departure_places on ride.departure_place_id = departure_places.id')
.joins('inner join places as arrival_places on ride.arrival_place_id = arrival_places.id')
.joins('inner join place_translations as departure_place_translations on departure_places.id = departure_place_translations.place_id AND departure_place_translations.locale = "en"')
.joins('inner join place_translations as arrival_place_translations on arrival_places.id = arrival_place_translations.place_id AND arrival_place_translations.locale = "en"')
.order('departure_place_translations.name, arrival_place_translations.name')
.where(ride_id: 1)
.paginate(page: 1, per_page: 20)
.preload(
  departure_place: :translations,
  arrival_place: :translations
)
.to_a

What we do here:

• First make some custom SQL with INNER JOINs where our order constraint can be fulfilled (Power of plain SQL: Using eager_load here is not possible or very painful)
• Then preload the result set (Power of ActiveRecord: If you don't use ActiveRecord preload you need to manually take care of pagination and ordering after fetching the records by ids)