Filtering belongs_to drop-down in administrate dashboard

Question

I have an administrate dashboard in a Rails (6.1.5) that allows administrators to add shortlisters and assign them an allocation of projects. Projects are in events. The drop-down by which an event is added when creating a shortlister comes from these fragments of the event_shortlister_dashboard.rb

ATTRIBUTE_TYPES = {
  shortlister: Field::BelongsTo,
  event: Field::BelongsTo,
  project_allocation: Field::Number,
  category: Field::Select.with_options(
    collection: Project::CATEGORIES.values,
    include_blank: true
  ),
  id: Field::Number,
  created_at: Field::DateTime,
  updated_at: Field::DateTime
}.freeze

FORM_ATTRIBUTES = %i[
  shortlister
  event
  project_allocation
  category
].freeze

Instead of the drop-down containing all events I want to filter it so that it only contains the events with their phase property set to 'registrations_closed'.

I tried doing this by extending the model and adding another belongs_to relationship, i.e.

class EventShortlister < ApplicationRecord
  belongs_to :event
  belongs_to :registration_closed_event,
             -> { where(phase: 'registrations_closed') },
             class_name: 'Event'

and then including this new dropdown in the dashboard ATTRIBUTE_TYPES:

registration_closed_event: Field::BelongsTo.with_options(class_name: 'Event')

but this gave an error when loading the page:

undefined method `registration_closed_event_id'

What should I change to achieve this filtering, and where?

I wondered if I should add/edit a scoped_resource method, but where?

Answer 1

Yes, administrate provides custom scopes as well you can provide in options like:

registration_closed_event: Field::BelongsTo.with_options(class_name: 'Event', scope: -> { Event.where(phase: 'registrations_closed') })

You can refer to the documentation for more information https://github.com/thoughtbot/administrate/blob/main/docs/customizing_dashboards.md under Customizing Fields -> Field::BelongsTo section where it has a custom scope support option there. Hope this helps.