Use foreign_key

Author: grzegorz-jakubiak

lib/active_admin/mongoid/association/relatable.rb

@@ -6,4 +6,9 @@ def macro
   def embeds?
     [:embeds_one, :embeds_many].include?(macro)
   end
+
+  def foreign_key
+    return if embeds?
+    foreign_key.to_sym rescue nil
+  end
 end

lib/active_admin/mongoid/filters/resource_extension.rb

@@ -6,7 +6,7 @@ def default_association_filters
       without_embedded = resource_class.reflect_on_all_associations.reject { |e| e.embeds? }
       poly, not_poly = without_embedded.partition{ |r| r.macro == :belongs_to && r.options[:polymorphic] }
 
-      filters = poly.map(&:foreign_type) + not_poly.map(&:name)
+      filters = poly.map(&:foreign_key) + not_poly.map(&:name)
       filters.map &:to_sym
     else
       []