HasMany relationships load all objects and then count on collection page

Created by: RCulpepp

• What were you trying to do? I was attempting to load an index of resources that had hundreds of thousands of associated resources through a has_many relationship. When querying, it is attempting to load all objects in memory, before counting. Thus slowing down the app (unnecessarily and unexpectedly) since all that displays is a count for those associated objects.

I have something like this:

resource_dashboard.rb

ATTRIBUTE_TYPES = {
  associated_resources: Field::HasMany
}.freeze

COLLECTION_ATTRIBUTES = [
  :associated_resources,
].freeze

• What did you end up with (logs, or, even better, example apps are great!)? A very slow response!

I've come up with a solution that'll I'll submit as a PR.

• What versions are you running?
  • Rails 5.0.7.2
  • administrate 0.11.0