Problem on Rails fixtures creation sequence - ruby-on-rails

Question

I am reading the book Simply Rails by Sitepoint and given these models:
story.rb
class Story < ActiveRecord::Base
validates_presence_of :name, :link
has_many :votes do
def latest
find :all, :order => 'id DESC', :limit => 3
end
end
def to_param
"#{id}-#{name.gsub(/\W/, '-').downcase}"
end
end
vote.rb
class Vote < ActiveRecord::Base
belongs_to :story
end
and given this fixtures
stories.yml
one:
name: MyString
link: MyString
two:
name: MyString2
link: MyString2
votes.yml
one:
story: one
two:
story: one
these tests fail:
story_test.rb
def test_should_have_a_votes_association
assert_equal [votes(:one),votes(:two)], stories(:one).votes
end
def test_should_return_highest_vote_id_first
assert_equal votes(:two), stories(:one).votes.latest.first
end
however, if I reverse the order of the stories, for the first assertion and provide the first vote for the first assertion, it passes
story_test.rb
def test_should_have_a_votes_association
assert_equal [votes(:two),votes(:one)], stories(:one).votes
end
def test_should_return_highest_vote_id_first
assert_equal votes(:one), stories(:one).votes.latest.first
end
I copied everything as it is in the book and have not seen an errata about this. My first conclusion was that the fixture is creating the records from bottom to top as it was declared, but that doesn't make any point
any ideas?
EDIT: I am using Rails 2.9 running in an RVM

Answer 1

Your fixtures aren't getting IDs 1, 2, 3, etc. like you'd expect - when you add fixtures, they get IDs based (I think) on a hash of the table name and the fixture name. To us humans, they just look like random numbers.
Rails does this so you can refer to other fixtures by name easily. For example, the fixtures
#parents.yml
vladimir:
name: Vladimir Ilyich Lenin
#children.yml
joseph:
name: Joseph Vissarionovich Stalin
parent: vladimir
actually show up in your database like
#parents.yml
vladimir:
id: <%= fixture_hash('parents', 'vladimir') %>
name: Vladimir Ilyich Lenin
#children.yml
joseph:
id: <%= fixture_hash('children', 'joseph') %>
name: Joseph Vissarionovich Stalin
parent_id: <%= fixture_hash('parents', 'vladimir') %>
Note in particular the expansion from parent: vladimir to parent_id: <%= ... %> in the child model - this is how Rails handles relations between fixtures.
Moral of the story: Don't count on your fixtures being in any particular order, and don't count on :order => :id giving you meaningful results in tests. Use results.member? objX repeatedly instead of results == [obj1, obj2, ...]. And if you need fixed IDs, hard-code them in yourself.
Hope this helps!
PS: Lenin and Stalin weren't actually related.

Answer 2

Xavier Holt already gave the main answer, but wanted to also mention that it is possible to force rails to read in fixtures in a certain order.
By default rails assigns its own IDs, but you can leverage the YAML omap specification to specify an ordered mapping
# countries.yml
--- !omap
- netherlands:
id: 1
title: Kingdom of Netherlands
- canada:
id: 2
title: Canada
Since you are forcing the order, you have to also specify the ID yourself manually, as shown above.
Also I'm not sure about this part, but I think once you commit to overriding the default rails generated ID and use your own, you have to do the same for all downstream references.
In the above example, suppose each country can have multiple leaders, you would have do something like
# leaders.yml
netherlands-leader:
country_id: 1 #you have to specify this now!
name: Willem-Alexander
You need to manually specify the id that refers to the previous Model (Countries)