nested_has_many_through

A fantastic patch/plugin has been floating around for a while:

• http://dev.rubyonrails.org/ticket/6461
• http://code.torchbox.com/svn/rails/plugins/nested_has_many_through

obrie made the original ticket and Matt Westcott released the first version of the plugin, under the MIT license. Many others have contributed, see the trac ticket for details.

Here is a refactored version (I didn’t write the original), suitable for edge/2.0-stable with a bunch of acceptance specs. I’m concentrating on plugin usage, once it becomes stable, and well enough speced/understood, then it’s time to pester rails-core.

Why republish this on github?

• The previous implementations are very poorly speced/tested, so it’s pretty hard to refactor and understand this complicated bit of sql-fu, especially when you’re aiming at a moving target (edge)
• the lastest patches don’t apply on edge
• github - let’s collab to make this better and get a patch accepted, fork away!

Help out

I’m releasing ‘early and often’ in the hope that people will use it and find bugs/problems. Report them at http://ianwhite.lighthouseapp.com, or fork and pull request, yada yada.

History

Here’s the original description:

  This plugin makes it possible to define has_many :through relationships that
  go through other has_many :through relationships, possibly through an
  arbitrarily deep hierarchy. This allows associations across any number of
  tables to be constructed, without having to resort to find_by_sql (which isn't
  a suitable solution if you need to do eager loading through :include as well).

Show me the money!

Here’s some models from the specs:

  class Author < User
    has_many :posts
    has_many :categories, :through => :posts, :uniq => true
    has_many :similar_posts, :through => :categories, :source => :posts
    has_many :similar_authors, :through => :similar_posts, :source => :author, :uniq => true
    has_many :posts_of_similar_authors, :through => :similar_authors, :source => :posts, :uniq => true
    has_many :commenters, :through => :posts, :uniq => true
  end

  class Post < ActiveRecord::Base
    belongs_to :author
    belongs_to :category
    has_many :comments
    has_many :commenters, :through => :comments, :source => :user, :uniq => true
  end

The first two has_manys of Author are plain vanilla, the last four are what this plugin enables

  # has_many through a has_many :through
  has_many :similar_posts, :through => :categories, :source => :posts

  # doubly nested has_many :through
  has_many :similar_authors, :through => :similar_posts, :source => :author, :uniq => true

  # whoah!
  has_many :posts_of_similar_authors, :through => :similar_authors, :source => :posts, :uniq => true

  # has_many through a has_many :through in another model
  has_many :commenters, :through => :posts, :uniq => true

What does it run on?

Currently it’s running on edge, 2.0-stable and 2.0.2

If you want to run the CI suite, then check out garlic_example.rb (The CI suite is being cooked with garlic - git://github.com/ianwhite/garlic)