[Suggestion] Add support for eager loading optionally

[rafacoello]

Hello. I would like to ask you if there is an specific reason why not to optionally allow eager load of relationships on locate/locate_many.
I mean something like this:

def locate_many(gids, options = {})
  models_and_ids = gids.collect { |gid| [ gid.model_class, gid.model_id ] }
  ids_by_model = models_and_ids.group_by(&:first)
  loaded_by_model = Hash[ids_by_model.map do |model, ids|
    [ model, find_records(model, ids.map(&:last), includes: options[:includes], ignore_missing: options[:ignore_missing]).index_by { |record| record.id.to_s } ]
  end]

  models_and_ids.collect { |(model, id)| loaded_by_model[model][id] }.compact
end

private
 def find_records(model_class, ids, options)
    if options[:ignore_missing]
      model_class.includes(options[:includes]).where(id: ids)
    else
      model_class.includes(options[:includes]).find(ids)
    end
  end
def 

It would be not exactly like that code, but well, it's an idea.

Thanks in advance

[rafaelfranca]

Can you explain how that would be used and why?

[rafacoello]

Hello @rafaelfranca
ActiveRecord supports eager load (using includes method). This is useful in some cases that you know you will be calling a lot the relationships of a model, so you end having an N+1 queries issue.

E.g.

users = User.find([ 1, 2 ]) # This generates a query SELECT * FROM users WHERE id IN (1, 2)
users.first.posts # This generates a query SELECT * FROM posts WHERE user_id = 1
users.first.posts # This generates a query SELECT * FROM posts WHERE user_id = 1 again.

In the other hand:

users = User.includes(:posts).find([ 1, 2 ]) # This generates both queries (SELECT * FROM users WHERE id IN (1, 2)) and (SELECT * FROM posts WHERE user_id IN (1, 2))
users.first.posts # No query
users.last.posts # No query 

If we had this feature here, we could do something like GlobalID::Locator.locate_many([ user_gid_1, user_gid_2 ], {includes: :posts}) which would eager load the posts.

I know that can be done with a custom Locator (which I already did for my case) but I thought that having that option could be useful to anyone as it is very generic.

[rafaelfranca]

Makes sense. Do you want to open a PR for it?

[rafacoello]

Sure. Thanks! @rafaelfranca