Support association search for other types of association fields

[josephktcheung]

This issue and the proposed fix is very similar to #1176

Right now association search doesn't work for new types of association fields.

Administrate::Search hard-codes the possible types of association fields in a list to determine if association search should be used. This means that new types of fields cannot perform association search and things break.

My proposed solution (see lib/administrate/search.rb) does a programmatic search for field classes that inherit from Administrate::Field::Associative. This allows plugin authors not to worry about adding their new type to a list or any other sort of setup.

A potential problem with this approach is that it includes Administrate::Field::Polymorphic on the list. I don't know if this can cause problems down the line or not.

[hound]

Layout/TrailingWhitespace: Trailing whitespace detected.

[jshum]

^ any updates on this? I'm seeing this issue as well on my setup
cc: @nickcharlton

[seanpdoyle]

As an alternative to mapping over ObjectSpace (and maybe even skipping the memoization), have you considered using Class#descendants?

class C; end
C.descendants # => []

class B < C; end
C.descendants # => [B]

class A < B; end
C.descendants # => [B, A]

class D < C; end
C.descendants # => [B, A, D]

[egreer]

Could also use ancestors from the deferred_class to see if it includes Administrate::Field::Associative. This would allow for any plugins that extend the BelongTo, HasMany etc to also be included.

This could be:

  def association_search?(attribute)
      return unless attribute_types[attribute].respond_to?(:deferred_class)
      attribute_types[attribute].deferred_class.ancestors.include?(Administrate::Field::Associative)
  end

[pablobm]

In defence of this solution, I'd say it just does the same thing that already happens at lib/administrate/base_dashboard.rb (and I myself introduced at #1176).

I'd be happy with merging this, then having another PR to refactor both instances.