STI subclassing

rubyonrails-talk
1

Hi, all. I'm wrestling with subclassing models in AR. Wondering if i'm running up against a limitation on sub-subclassing, or if the syntax has gone awry here.

My app has BlogPosts, which are a sub of Articles. It's got Writers < RegisteredUsers < Users.

When I try to call registered_user on a BlogPost, I get nil.

Any & all help appreciated.

class Article < ActiveRecord::Base   etc....

end

class BlogPost < Article   validates_presence_of :section_id, :title, :body   belongs_to :registered_user

end

class NewsArticle < Article belongs_to :writer end

require "digest/md5" class User < ActiveRecord::Base etc... end

class RegisteredUser < User    validates_uniqueness_of :name    has_many :comments    has_many :events, :class_name => "Article", :foreign_key => "user_id"    has_many :blog_posts, :class_name => "Article", :foreign_key => "user_id" end

class Writer < RegisteredUser   has_many :news_articles, :class_name => "Article", :foreign_key => "user_id" end

@post=BlogPost.find(:first, :conditions=>'user_id=1')

=> #<BlogPost id: 505, title: "Cubs outlook", type: "BlogPost", user_id: 1>

User.find(1)

=> #<Writer id: 1, type: "Writer">

@post.registered_user

=> nil

2

magic_hat wrote:

My app has BlogPosts, which are a sub of Articles. It's got Writers < RegisteredUsers < Users.

When I try to call registered_user on a BlogPost, I get nil.

Any & all help appreciated.

class Article < ActiveRecord::Base   etc....

end

class BlogPost < Article   validates_presence_of :section_id, :title, :body   belongs_to :registered_user

end

class NewsArticle < Article belongs_to :writer end

require "digest/md5" class User < ActiveRecord::Base etc... end

class RegisteredUser < User    validates_uniqueness_of :name    has_many :comments    has_many :events, :class_name => "Article", :foreign_key => "user_id"    has_many :blog_posts, :class_name => "Article", :foreign_key => "user_id" end

class Writer < RegisteredUser   has_many :news_articles, :class_name => "Article", :foreign_key => "user_id" end

@post=BlogPost.find(:first, :conditions=>'user_id=1')

=> #<BlogPost id: 505, title: "Cubs outlook", type: "BlogPost", user_id: 1>

User.find(1)

=> #<Writer id: 1, type: "Writer">

@post.registered_user

=> nil

You should instead have:

belongs_to :registered_user, :foreign_key => :user_id

A Rails bug meant that you didn't get an error message.

3

That works. Thanks.

One other issue that's cropping up.

The STI inheiritance has some weird loading behavior. Writers are not found with RegisteredUser.find until after they've been loaded with Writer.find:

RegisteredUser.find_by_name('John Doe')

=> nil

Writer.find_by_name('John Doe')

=> #<Writer id: 1, name: "John Doe">

RegisteredUser.find_by_name('John Doe')

=> #<Writer id: 1, name: "John Doe">

Any idea what that's all about?

4

magic_hat wrote:

The STI inheiritance has some weird loading behavior. Writers are not found with RegisteredUser.find until after they've been loaded with Writer.find:

RegisteredUser.find_by_name('John Doe')

=> nil

Writer.find_by_name('John Doe')

=> #<Writer id: 1, name: "John Doe">

RegisteredUser.find_by_name('John Doe')

=> #<Writer id: 1, name: "John Doe">

Any idea what that's all about?

Yes, STI subclasses aren't added to find conditions until they're loaded.

One way to force loading of subclasses is to call require_dependency at the bottom of model files. e.g. require_dependency 'writer'.

Another way is to name each leaf STI class in environment.rb, which forces loading of all classes up the tree.

You may have to use method 2 for production mode and method 1 for other modes.

There's also this plugin, which I haven't yet tried:    http://agilewebdevelopment.com/plugins/has_types