Many To Many Relationship help needed


I have 3 models:

class Result < ActiveRecord::Base
has_many :collections
has_many :articles, :through => :collections

class Article < ActiveRecord::Base
has_many :collections
has_many :results, :through => :collections

class Collection < ActiveRecord::Base
belongs_to :result
belongs_to :article

Collection has a table like this:
create_table :collections do |t|
t.column :id, :integer
t.column :result_id, :integer
t.column :article_id, :integer
t.column :extract, :text

The problem i have is this.
I do a find for a single result.
Then i go through each article in this result, using the each method.

At this point i’m outputting all the attributes of articles.
But i want to also output the extract for this article and result.

How would i do this?

article.extract doesn’t work, nor does article.results.extract

Thanks for your help.

In your design article has many collections therefor article also has
many extracts. Which means that article will not have an extract
method which is why article.extract will not work.

In the same way article.results method will give you an Array of
Result object so obviously will not have an extract method. This is
why articles.results.extract will not work.

Maybe that will help you rethink your design to produce your desired

Oops slight typo in previous post


should have been


But, won’t this run SQL query for each article in result?

There must be an easy way to combine both article and result, using

I’ll use this for now, until i find something better.

On Tue, February 20, 2007 10:58 pm, Jon G. wrote:


How would i do this?

email: [email protected]

You’ll need to find the collection and use collection.extract. Easiest
might be something like…

result.articles.each do |article|
collection = article.collections.find(:first, :conditions =>
[“result_id = ?”,])

This assumes that there’s only ever one collection associated with any
article/result pair.

I understand. I thought because i’ve combined both article and result
using collection,
the extract attribute might be included in both.

There must be a nice and simple way to do this, without going through
every article, or

Anyway, thanks for your help.

On Tue, February 20, 2007 10:53 pm, Robert W. wrote:

On Feb 20, 5:50 pm, “Robert W.” [email protected] wrote:


class Result < ActiveRecord::Base has_many :collections has_many :articles, :through
create_table :collections do |t| t.column :id, :integer t.column :result_id, :integer

email: [email protected]

use eager loading. That will only take one SQL query, and you will
have all the stuff you need in your result.
(code not tested and probably contains typos :wink: )

@result = Result.find :first, :conditions => [someting], :include =>
{:collections => :articles }

<%= @result.collections.each do |coll| %>
… access the extract…
<%= coll.extract %>
…access the article attributes with:…
<%= coll.article.some_attribute %>