has_many :through should work if the join model uses has_one relationship

Is it not permissible to have a bug open on this as something to fix at some point? The workaround is not something I would like to do.

Well, this seems to work as a hackish work-around and relatively efficient if most of your posts have a photo. I'm not really an SQL guru so if someone could post better SQL that would be nice :-)

@photos = @user.posts.map { |post| post.photo } .compact

This patch seems to work for me, but I really don't know enough about the inner workings of associations to be sure.

verified that the patch applies to 2-3-stable and tests pass for mysql/sqlite/postgres. Going to look a little deeper now for potential problems...

After looking at this deeper the main problem is with inserting and deleting records via the has_many :through => has_one relationship. However the main use case of this association is read-only anyway, so I think there is good value here, and I believe Josh's patch works smoothly because of support for has_many :through has_many.

I believe the proper thing to do here is add an exception similar to HasManyThroughCantAssociateThroughHasManyReflection to make the read-only functionality explicit and update the documentation. I'm willing to do that now if there is agreement that this is the right approach.

Oops, I left an unused Exception in there. That is removed in this updated patch for 2-3-stable, and also I have a rebased version to apply to master.

I've attached a patch.

Per koz's request, here is an updated patch with an official deprection for the old exception for the 2-3 branch.

+1 for the functionality. I could use this behavior one of my current projects.

Unfortunately, I wasn't able to apply your last version of the patch against 2-3-stable or master.

+1 Verified

Cleanly applies (apart from whitespace warning) and passes on master and 2-3-stable.

Sorry, doesn't apply on the latest versions as Josh pointed out.

Here are updated patches for 2-3-stable and master. Handy-dandy one-stop location:

Crap. The deprecation snuck into master diff as well, which I don't think it should be according to my impression from koz. Without the deprecation:

Verified that the patch applies to 2-3-stable and master, and that the functionality works as expected through manual testing.

I ran these commands:

rails 2719-demo
cd 2719-demo
script/generate  model user
script/generate  model post user_id:integer
script/generate  model photo post_id:integer
rake db:create db:migrate

Then used these models:

class User < ActiveRecord::Base
  has_many :posts
  has_many :photos, :through => :posts
end







class Post < ActiveRecord::Base
  belongs_to :user
  has_one :photo
end







class Photo < ActiveRecord::Base
  belongs_to :post
end

And then played around in script/console:

>> user = User.create!
=> #<User id: 2, created_at: "2009-08-09 20:51:27", updated_at: "2009-08-09 20:51:27">
>> post = user.posts.create
=> #<Post id: 3, user_id: 2, created_at: "2009-08-09 20:51:34", updated_at: "2009-08-09 20:51:34">
>> post.create_photo
=> #<Photo id: 3, post_id: 3, created_at: "2009-08-09 20:51:37", updated_at: "2009-08-09 20:51:37">
>> user.photos
=> [#<Photo id: 3, post_id: 3, created_at: "2009-08-09 20:51:37", updated_at: "2009-08-09 20:51:37">]

(from [b763858ed5faeda720035dd2178e7c44aa34240a]) Enable has_many :through for going through a has_one association on the join model [#2719 has_many :through should work if the join model uses has_one relationship state:resolved]

Signed-off-by: Pratik Naik pratiknaik@gmail.com
http://github.com/rails/rails/commit/b763858ed5faeda720035dd2178e7c...