inflate_has_many.rb

module InflateHasMany
  # what #inflate is to `belongs_to` associations, #inflate_has_many is
  # to `has_many` associations
  # see: https://gist.github.com/pmn4/eb497edad63065304383bdfcf8d60b47
  #
  # returns a flatmap of all resources
  def inflate_has_many(models, foreign_key, key = self.name.underscore.pluralize.to_sym, resources: nil)
    models = Array(models)

    # determine the set of unique, non-nil model ids
    ids = models.map(&:id).uniq.compact

    # fetch all resources which are referenced by any model
    # then group them for fast lookup later
    resources ||= where(foreign_key => ids)
    resources_map = resources.group_by { |r| r.send(foreign_key) }

    # models can be an array of anything, that is, items in the array do not
    # have to be of the same class, just just have to respond to the key
    # provided (well, the "assignment to" the key provided)
    models
      .select { |m| m.respond_to?(:"#{key}=") }
      .each do |model|
        association = model.association(key)
        # using CollectionAssociation#replace here could result in a query.
        # instead, we write more directly to the target array
        if resources_map.key?(model.id)
          resources_map[model.id]
            .each { |r| association.add_to_target(r, true) }
        end
        # inform the association that it has been loaded, so that subsequent
        # fetches do not result in a database query
        association.loaded!
      end

    resources
  end
end