Post Type/Abstraction with single table inheritance

[ryanburnette]

STI works now. I have Page inheriting from Post.

[ryanburnette]

Do I need to create an index for type when using STI?

[paulelliott]

You don't need to, but I would probably out one on the type and id combination.

On Sunday, February 9, 2014, Ryan Burnette notifications@github.com wrote:

Do I need to create an index for type when using STI?

Reply to this email directly or view it on GitHubhttps://github.com/ryanburnette/rcms/issues/14#issuecomment-34592598 .

-- Paul

[ryanburnette]

Roger that. Thanks.

On Sun, Feb 9, 2014 at 7:34 PM, Paul Elliott notifications@github.comwrote:

You don't need to, but I would probably out one on the type and id combination.

On Sunday, February 9, 2014, Ryan Burnette notifications@github.com wrote:

Do I need to create an index for type when using STI?

Reply to this email directly or view it on GitHub< https://github.com/ryanburnette/rcms/issues/14#issuecomment-34592598> .

-- Paul

— Reply to this email directly or view it on GitHubhttps://github.com/ryanburnette/rcms/issues/14#issuecomment-34593102 .

[ryanburnette]

I hadn't read anything about this in documentation, but it appears that STI doesn't mean that you inherit the relationships. If I set up a habtm relationship between Asset and Post, and Page is inheriting from Post, it doesn't seem to inherit the relationship with Asset. I assume I'd have to define that relationship between Asset and Page explicitly and create another join table for each inherited type.

[paulelliott]

If you are subclassing the parent model then you should receive all the same associations.

[ryanburnette]

I must be doing something wrong. I'll review this.

[ryanburnette]

@paulelliott I just played around with this a bit and I'm not sure what I've missed.

The Post model has a many_to_many association with the Image model which works fine for Post. https://github.com/ryanburnette/rcms/blob/master/app/models/post.rb

The Page model inherits from Post, but the images method is not defined for it. https://github.com/ryanburnette/rcms/blob/master/app/models/page.rb

2.1.0 :016 > Post.first.images
  Post Load (0.4ms)  SELECT `posts`.* FROM `posts` ORDER BY `posts`.`id` ASC LIMIT 1
  Image Load (0.4ms)  SELECT `images`.* FROM `images` INNER JOIN `images_posts` ON `images`.`id` = `images_posts`.`image_id` WHERE `images_posts`.`post_id` = 1
 => #<ActiveRecord::Associations::CollectionProxy []>
2.1.0 :017 > Page.first.images
  Page Load (0.4ms)  SELECT `posts`.* FROM `posts` WHERE `posts`.`type` IN ('Page') ORDER BY `posts`.`id` ASC LIMIT 1
NoMethodError: undefined method `images' for nil:NilClass
    from (irb):17
    from /Users/ryan/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands/console.rb:90:in `start'
    from /Users/ryan/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands/console.rb:9:in `start'
    from /Users/ryan/.rvm/gems/ruby-2.1.0/gems/railties-4.0.2/lib/rails/commands.rb:62:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'
2.1.0 :018 >

Any advice on what to look into to troubleshoot? I just assumed when I first saw this that the the associations were not inherited.

[paulelliott]

There error you posted isn't saying that the association isn't there. It is saying that Page.first returned a nil. Try doing Page.new.images and see what it says.

[ryanburnette]

So the weirdness was that Page.first was returning nil. I don't know how that was possible as there were several pages in existence. I removed them all, added a few new pages and it behaves as it should. Strange.

Another thing I noticed is that Post.all return all posts and the inherited type objects. I had to change my methods in PostController to make them specific to just posts. If I had to do it over I would create a model for Post and Page inherit from so they'd both have their types explicitly defined. I can think of other cases where the natural behavior of STI, however, would be desirable.