Question

I have 4 models: transac, transac_data, item, dvd_details

class Transac < ActiveRecord::Base
  has_many :transac_datas
  has_many   :items, :through => :transaction_datas
end

class TransactionData < ActiveRecord::Base
  belongs_to :item
  belongs_to :transaction
end

class Item < ActiveRecord::Base
  has_many   :transaction_datas
  has_many   :transacs, :through => :transaction_datas
end

class DvdDetails < ActiveRecord::Base
  has_many :items
end

Now in the “transac” view, I need to access stuff from all these models like:

<td><%=h transac.status %></td>
<% transac.transaction_datas.each do |td| %>
  <td><%=h td.item_type %></td>
<% end %>

<% transac.items.each do |item| %>
  <td><%=h item.item_type %></td>
<% end %>

BUT I also need to access some info from the “DvdDetails” model which is the “furthest” away from transac.

I realized that doing something like this wouldn’t really work:

class Transac < ActiveRecord::Base
  has_many :transac_datas
  has_many :items, :through => :transaction_datas
  has_many :dvd_details, :through => :items, :through => :transaction_datas
end

and do this in the index of “transac” view

<%=h transac.dvd_details.name %>

What do I need to do to accomplish this?

Any help is appreciated!
Thank you!

Answer 1

Actually, with Ian White’s nested_has_many_through plugin, you can daisy-chain has_many throughs the way you want. Just install the plugin like so:

script/plugin install git://github.com/ianwhite/nested_has_many_through.git

Then setup your model like this:

class Transac < ActiveRecord::Base
  has_many :transaction_datas
  has_many :items, :through => :transaction_datas
  has_many :dvd_details, :through => :items
end

This should do what you need.

UPDATE: This question has come up a few times recently. I wrote an article, nesting your has_many :through relationships, to explain in detail. It even has an accompanying example application on GitHub to download and play around with.