a bug in has_many :through/lazy loading?

rubyonrails-talk
1

Hi everybody,

I think I've encountered a very funny bug in the has_many :through, but I'm not sure if it me doing something wrong. Let me post the example.

Consider the following migration/database structure:

create_table :books do |t|    t.column :title,:string end

create_table :authors do |t|    t.column :name,:string end

create_table :authorships do |t|    t.column :book_id, :numeric    t.column :author_id, :numeric end

And the following models:

class Author < ActiveRecord::Base    has_many :authorships, :dependent => true    has_many :books, :through => :authorships end

class Authorship < ActiveRecord::Base    belongs_to :book    belongs_to :author end

class Book < ActiveRecord::Base    has_many :authorships, :dependent => true    has_many :authors, :through => :authorships end

Now to the funny part. If I do something like this

b = Book.create(:title => 'A Book') a = Author.create(:name => 'An Author') Authorship.create(:book => b, :author => a) puts b.authors.length

It will of course output 1

HOWEVER, if I read the b.authors before creating an association, the b.authors won't get updated! So, in this example, having

b = Book.create(:title => 'A Book') a = Author.create(:name => 'An Author')

puts b.authors.length # ACCESSING THE COLLECTION HERE

Authorship.create(:book => b, :author => a)

puts b.authors.length

Will output both times a zero!

2

Try: puts b.authors(true).size

See the section of

under the "Caching" heading

-Rob

Rob Biedenharn http://agileconsultingllc.com Rob@AgileConsultingLLC.com

3

I don't think it's a bug (from what i remember of the Rail's Pragmatic book) because the association isn't reloaded. if you do : b.authors(true).length for reload = true which is set to false by default, you'll get the right answer. But then the railsway to do it is : b = Book.create(:title => 'A Book') a = Author.create(:name => 'An Author') b.authors << a and the reload is (should be) done automatically

Charly