Rails has_many through any? / empty? - ruby-on-rails

Question

I found an unusual situation on rails 3 app.
Consider the following model:
class Genre < ActiveRecord::Base
has_many :banner_genres, :dependent => :destroy
has_many :banners, :through => :banner_genres
...
class BannerGenre < ActiveRecord::Base
attr_accessible :banner_id, :banner, :genre_id, :genre, :position
belongs_to :genre
belongs_to :banner
...
class Banner < ActiveRecord::Base
has_many :banner_genres, :dependent => :destroy
has_many :genres, :through => :banner_genres
...
Now if I have a genre with a banner, I get the following lines in rails console:
1.9.3p362 :005 > g = Genre.find 62
Genre Load (0.8ms) SELECT "genres".* FROM "genres" WHERE "genres"."id" = $1 LIMIT 1 [["id", 62]]
=> #<Genre id: 62, ...
1.9.3p362 :006 > g.banner_genres.any?
(0.5ms) SELECT COUNT(*) FROM "banner_genres" WHERE "banner_genres"."genre_id" = 62
=> true
1.9.3p362 :007 > g.banners
Banner Load (1.0ms) SELECT "banners".* FROM "banners" INNER JOIN "banner_genres" ON "banners"."id" = "banner_genres"."banner_id" WHERE "banner_genres"."genre_id" = 62 ORDER BY position
=> [#<Banner id: 446, ...
1.9.3p362 :008 > g.banners.any?
=> false
Why does the .any? returns false? I thy with another has_many through association on the same project and it returns true.
Edit:
I had a typo when passing the code here. It's banner_genres on the has_many. Not genre_banners.
Also the inverse association works as it's supposed to:
1.9.3p362 :004 > b = Banner.find 446
Banner Load (1.1ms) SELECT "banners".* FROM "banners" WHERE "banners"."id" = $1 ORDER BY position LIMIT 1 [["id", 446]]
=> #<Banner id: 446...
1.9.3p362 :005 > b.genres.any?
(0.8ms) SELECT COUNT(*) FROM "genres" INNER JOIN "banner_genres" ON "genres"."id" = "banner_genres"."genre_id" WHERE "banner_genres"."banner_id" = 446
=> true
Edit 2
More strange console output:
1.9.3p362 :007 > g.banners.class
=> Array
1.9.3p362 :008 > g.banners.any?
=> false
1.9.3p362 :004 > g.banners.any? {|b| b}
=> true
1.9.3p362 :006 > g.banners.count
(0.9ms) SELECT COUNT(*) FROM "banners" INNER JOIN "banner_genres" ON "banners"."id" = "banner_genres"."banner_id" WHERE "banner_genres"."genre_id" = 62
=> 1
1.9.3p362 :009 > g.banners.to_a.any?
=> true
Edit 3
g.banner_genres
BannerGenre Load (0.7ms) SELECT "banner_genres".* FROM "banner_genres" WHERE "banner_genres"."genre_id" = 62
=> [#<BannerGenre id: 4, genre_id: 62, banner_id: 446, position: 1, created_at: "2013-03-15 16:41:10", updated_at: "2013-03-15 16:41:10">]
Edit 4 Asked by Aleks
could you please show queries that are shown on g.banners.any? and g.banners.
It's exactly the same query, which it's even stranger. I also didn't override the any? method anywhere.
1.9.3p362 :037 > g.banners(true)
Banner Load (1.0ms) SELECT "banners".* FROM "banners" INNER JOIN "banner_genres" ON "banners"."id" = "banner_genres"."banner_id" WHERE "banner_genres"."genre_id" = 62 ORDER BY position
=> [#<Banner id: 446, ...
1.9.3p362 :038 > g.banners(true).any?
Banner Load (1.2ms) SELECT "banners".* FROM "banners" INNER JOIN "banner_genres" ON "banners"."id" = "banner_genres"."banner_id" WHERE "banner_genres"."genre_id" = 62 ORDER BY position
=> false
1.9.3p362 :039 > g.banners.method(:any?)
=> #<Method: Array(Enumerable)#any?>

Answer 1

any? was supposed to return true....
I was so curious about this issue that I decided to simulate it.
g = Genre.find 1
Genre Load (30.1ms) SELECT "genres".* FROM "genres" WHERE "genres"."id" = $1 LIMIT 1 [["id", 1]]
=> #<Genre id: 1, name: "a", created_at: "2013-03-19 11:44:32", updated_at: "2013-03-19 11:44:32">
g.banner_genres.any?
(0.3ms) SELECT COUNT(*) FROM "banner_genres" WHERE "banner_genres"."genre_id" = 1
=> true
g.banners
Banner Load (0.5ms) SELECT "banners".* FROM "banners" INNER JOIN "banner_genres" ON "banners"."id" = "banner_genres"."banner_id" WHERE "banner_genres"."genre_id" = 1
=> [#<Banner id: 1, name: "1", created_at: "2013-03-19 11:43:00", updated_at: "2013-03-19 11:43:00">, #<Banner id: 2, name: "2", created_at: "2013-03-19 11:43:59", updated_at: "2013-03-19 11:43:59">]
g.banners.any?
=> true
Also,
g.banners.class
=> Array
g.banners.any?
=> true
g.banners.to_a.any?
=> true
There is something else going on in your code...

Answer 2

The real question here is not whether the association is good or bad, but why it is showing false for array that has elements in it.
It is clear that it is returning values, but the question is why it is returning false
The explanation might lay here: Unable to get Ruby's #any? to return false with list of nil objects
See how the any? is implemented, and how it relates to your question, it might give you a hint.
See this link as well : http://apidock.com/ruby/Enumerable/any%3F
EDIT:
What you are saying:
First you have an array of objects. Which will on any? return false
But if you do .to_a you will do something like this:
Time.new.to_a #=> [39, 54, 8, 9, 4, 2013, 3, 99, true, "CET"]
And that is why it will return true, as you will have object that are not null.
EDIT 2
Just to note: any? will return false if all objects from an array are nil or false