Record exists when it doesn't - ruby-on-rails

Question

Given this simple model:
class Article < ActiveRecord::Base
validates :title, presence: true
validates :url, presence: true, uniqueness: true
validates :topic, presence: true
before_create :some_filter
private
def some_filter
self.noframe = false
end
end
And the fact that there are:
no observers
no indexes on the "noframe" column
How is this possible?
attrs = { title: "a", url: "http://www.example.com", topic: "test" }
Article.where(attrs).count
=> 0
Article.where(url:"http://www.example.com").count
=> 0
article = Article.new(attrs)
article.save
(0.2ms) BEGIN
Article Exists (0.6ms) SELECT 1 AS one FROM "articles" WHERE "articles"."url" = 'http://www.example.com' LIMIT 1
(0.3ms) ROLLBACK
article.errors.full_messages
[]
The debugger
When putting the debugger inside of "some_filter" method, this is what's happening.
[12] pry(#<Article>)> self.noframe = nil
=> nil
[13] pry(#<Article>)> self.valid?
Article Exists (0.5ms) SELECT 1 AS one FROM "articles" WHERE "articles"."url" = 'http://www.example.com' LIMIT 1
=> true
[14] pry(#<Article>)> self.noframe = false
=> false
[15] pry(#<Article>)> self.valid?
Article Exists (0.5ms) SELECT 1 AS one FROM "articles" WHERE "articles"."url" = 'http://www.example.com' LIMIT 1
=> true
[16] pry(#<Article>)> self.save
Article Exists (0.5ms) SELECT 1 AS one FROM "articles" WHERE "articles"."url" = 'http://www.example.com' LIMIT 1
=> false
More information
To make it more interesting, when I change "some_filter" to set noframe to either nil or to true, I can create as many records as I want without "Article Exists" error.
It also works when I set noframe attribute directly and not inside of before_create filter.
Why is this workaround working?
I'm able to "fix" it by replacing "before_create" with "after_create" and updating the noframe attribute additionally with update_attributes(noframe:false). But why is this a solution? update_attributes also calls all callbacks and validation so why is this not working in before_create?

Answer 1

before_create has one not that obvious property - if it returns false value it terminates whole saving chain. Same applies to all before-* callbacks. You can find it in callback documentation. Your method returns false, so whole transaction rolls back. Change it to:
def some_filter
self.noframe = false
true
end
And all will work.