Comments on: Learning Rails: Many-to-Many Relationships

By: dwhsix

dwhsix — Sun, 27 Apr 2008 15:26:21 +0000

Great example for a non-trivial m:m relationship. Wasn’t /exactly/ what I needed, but pointed me in the right direction to resolve a problem that had me baffled for a day…

By: grateful

grateful — Wed, 12 Dec 2007 19:25:23 +0000

Joel: I disagree with confused and reallyu appreciate the example. Yes, a couple of tables than the basics but it was based on a real world example of Flickr which made this tutorial different, and in my opinion, better. There are a handful of the way-too simplified versions out there for people who want the very basics. Your example had the added advantage of showing a real-world practical dimension that the others don’t due to the simplicity. Thanks!

By: Joel

Joel — Thu, 29 Nov 2007 04:10:50 +0000

@confused: while I understand your comment regarding the complexity of the tutorial, it was because I couldn’t find any tutorials that covered ordered-many-to-many relationships that I wrote this one. True, it does involve two relationships (collection-to-set and set-to-image) and thus has five tables, it was based on a real world (and highly useful) “gallery” system - flickr. So, I apologise for the complexity but countenance that this was about my learning process and the tips and tricks associated with how to do things when I couldn’t find relevant tutorials already in existence.

By: confused

confused — Thu, 29 Nov 2007 03:51:57 +0000

For the title “Learning Rails: Many-to-Many Relationships”, I don’t think you could have come up with a more confusing example. If you intend for beginners to “Learn” about “Many-to-Many Relationships”, a stripped down example (with 3 models maximum) would be more effective.

Thank you, none the less, for the code, once I decipher it.

By: Joel

Joel — Fri, 06 Jul 2007 06:08:25 +0000

You obviously failed to notice where it was filed (Ruby on Rails, design programming) or it's tags ( has many, many to many relationship, programming, Rails, Ruby, ruby on rails, through, tutorial) and those combined with the title referring to "Learning Rails" makes it pretty obvious that it was not about spilling my heart on life, love and women.

By: sarah

sarah — Fri, 06 Jul 2007 05:42:51 +0000

ok i decided to read this post as i thought it would be some heart felt spill on life and woman. PLEASE NEVER do that to me again!!! you are banned from providing misleading titles in you posts!!!

By: Joel

Joel — Tue, 19 Jun 2007 20:48:47 +0000

@Andrew: I will be writing up anything I find useful that I can't find assistance with on the web. In terms of a migration for the tables, it would look something like this (I'll update in the post too):

class CreateImages < ActiveRecord::Migration
  def self.up
    create_table :images do |t|
      t.column :name, :string, :null => false
      t.column :permalink, :string, :null => false
      t.column :description, :text, :null => false
      t.column :filename, :text, :null => false
    end
  end

  def self.down
    drop_table :images
  end
end

class CreateSets < ActiveRecord::Migration
  def self.up
    create_table :sets do |t|
      t.column :name, :string, :null => false
      t.column :permalink, :string, :null => false
      t.column :description, :text, :default => nil
    end
  end

  def self.down
    drop_table :sets
  end
end

and the complex join table

class CreateImagesets < ActiveRecord::Migration
  def self.up
    create_table :imagesets do |t|
      t.column :position, :int, :null => false
      t.column :gallery_id, :int, :null => false
      t.column :image_id, :int, :null => false
    end
    
    execute "alter table imagesets add foreign key (set_id) references sets(id)"
    execute "alter table imagesets add foreign key (image_id) references images(id)"
    
  end

  def self.down
    drop_table :imagesets
  end
end

By: Andrew

Andrew — Tue, 19 Jun 2007 15:23:34 +0000

Great tutorial… there should be more stuff like this out there.

One question: How would you set up the tables for this?

Thanks.

By: Fradam

Fradam — Mon, 04 Jun 2007 10:11:57 +0000

…due to a background in PHP, with itâ€™s rather lax type strictness….

Typo? I suspect you meant ‘almost non-existent’