Instance dependent association preloading which was removed has valid use cases

[agios]

4ed9797 removed support for preloading instance-dependent associations.

While it is understandable that they might have been a source of confusion, associations such as the one presented in #15024 which this addressed, can be properly preloaded in this manner:

class User < ActiveRecord::Base
  has_many :posts, ->(sender) {
    title_condition =
      if sender.is_a? User
        sender.name
      else # Relation
        User.arel_table[:name]
      end
    where(arel_table[:title].eq(title_condition))
  }
end

This code results in an association that can both be called on an instance as well as preloaded in another query. Removing this feature actually breaks working code.

What do you think @senny, @rafaelfranca?

[rafaelfranca]

It was already removed and we don't plan to add it back. Even that you can make it work it still have to check if you are in a instance. Also to make it work you are relying in private API of the framework arel_table.

[rafaelfranca]

This is a dup of #22560