Undefined Method for <ActiveRecord::Associations::CollectionProxy []>

[wkirby]

I am seeing this issue on Rails 6.0.2.1, Administrate 0.13.0 and the current master branch of NestedHasMany.

My configuration is very simple:

class LabDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    payor_lab_settings: Field::NestedHasMany.with_options(skip: :lab)
  }

  ...

  FORM_ATTRIBUTES = [
    :payor_lab_settings
  ].freeze
end

class PayorLabSettingDashboard < Administrate::BaseDashboard
  ATTRIBUTE_TYPES = {
    payor: Field::BelongsToSearch.with_options(class_name: 'Payor'),
  }.freeze
  
  ...

  FORM_ATTRIBUTES = [
    :payor
  ].freeze
end

Here is the relevant section of the stack trace:

PayorLabSetting::ActiveRecord_Associations_CollectionProxy#method_missing
activerecord (6.0.2.1) lib/active_record/relation/delegation.rb, line 108
Administrate::Page::Form#get_attribute_value
administrate (0.13.0) lib/administrate/page/base.rb, line 35
Administrate::Page::Form#attribute_field
administrate (0.13.0) lib/administrate/page/base.rb, line 29
block in Administrate::Page::Form#attributes
administrate (0.13.0) lib/administrate/page/form.rb, line 15
Administrate::Page::Form#attributes
administrate (0.13.0) lib/administrate/page/form.rb, line 14
Administrate::Field::NestedHasMany#nested_fields
() bundle/ruby/2.5.0/bundler/gems/administrate-field-nested_has_many-0145a35e4497/lib/administrate/field/nested_has_many.rb, line 23

The exact same code with Field::HasMany works correctly. All dashboards are working individually.

[wkirby]

Further digging, it looks like this is likely due to a change in Administrate between 0.12.0 and 0.13.0:

In 0.13.0 the relevant code: https://github.com/thoughtbot/administrate/blob/v0.13.0/lib/administrate/page/base.rb#L35

Vs 0.12.0: https://github.com/thoughtbot/administrate/blob/v0.12.0/lib/administrate/page/base.rb#L36

Administrate core stopped rescuing NameError and returning nil. My guess is if I revert back to 0.12.0 in Administrate, the code here was always technically broken, because of an attempt to initialize the Form with a collection, rather than an instance of the associated model, but because of Administrate's rescue, it wasn't blowing up, and instead returned a set of Fields with nil values.

[wkirby]

@nickcharlton I have opened PR #34 which addresses this problem. It also captures the same changes made in #31 and #32 in order to get tests passing against Administrate 0.13.0.

[karensg]

Confirming that the issue is solved with the PR.