Shows the other records that get destroyed when you destroy this one.

gistfile1.rbx

class ActiveRecord::Base
  def dependents(type=:destroy)
    reflections = self.class.reflect_on_all_associations
    reflections = reflections.select { |r| r.options[:dependent] == type }
    names = reflections.map(&:name)
    names.inject([]) do |list, name|
      list += send(name)
      list += send(name).map { |entity| entity.dependents rescue [] }
      list
    end.flatten.compact
  end
  
  def inspect_dependents
    dependents.inject({ }) do |memo, entity|
      name = entity.class.name.tableize
      memo[name] ||= []
      memo[name] << entity
      memo
    end
  end
end

gistfile2.rbx

class User < ActiveRecord::Base
  has_many :lists, :dependent => :destroy
  has_many :things # not dependent, so won't show up in results
end

class List < ActiveRecord::Base
  belongs_to :user
  has_many :items, :dependent => :destroy
end

class Item < ActiveRecord::Base
  belongs_to :list
end

# Should not show up in dependents list
class Thing < ActiveRecord::Base
  belongs_to :user
end

gistfile3.rbx

# creates seed data in script console
def create_seed_data
  print "=> creating seed data... "
  user = User.create!
  list = user.lists.create!
  list.items.create!
  list.items.create!
  user.things.create! # won't be in results
  puts "done!"
end

gistfile4.txt

>> create_seed_data
=> creating seed data... done!
=> nil
>> user = User.first
=> #<User id: 1, name: nil, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">
>> user.dependents
=> [#<List id: 1, user_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">, #<Item id: 1, list_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">, #<Item id: 2, list_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">]
>> user.inspect_dependents
=> {"items"=>[#<Item id: 1, list_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">, #<Item id: 2, list_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">], "lists"=>[#<List id: 1, user_id: 1, created_at: "2008-10-03 19:14:17", updated_at: "2008-10-03 19:14:17">]}
>> y _
--- 
items: 
- &id001 !ruby/object:Item 
  attributes: 
    updated_at: 2008-10-03 19:14:17
    id: "1"
    list_id: "1"
    created_at: 2008-10-03 19:14:17
  attributes_cache: {}

- &id002 !ruby/object:Item 
  attributes: 
    updated_at: 2008-10-03 19:14:17
    id: "2"
    list_id: "1"
    created_at: 2008-10-03 19:14:17
  attributes_cache: {}

lists: 
- !ruby/object:List 
  attributes: 
    updated_at: 2008-10-03 19:14:17
    id: "1"
    user_id: "1"
    created_at: 2008-10-03 19:14:17
  attributes_cache: {}

  items: 
  - *id001
  - *id002
=> nil
>> exit