ActiveRecord#first not returning the real first record

Question

I am having an issue with ActiveRecord#first seemingly not returning the first record all of the time.

>> Package.first
=> #<Package id: 22, name: "Test Package 4", created_at: "2009-09-11 21:10:54", updated_at: "2009-09-11 21:12:43", image_file_name: "0600-Sponsor.jpg", image_content_type: "image/jpeg", image_file_size: 29433>

What I'd really like to see is:

>> Package.first(:order => :id)
=> #<Package id: 13, name: "Default Package", created_at: "2009-09-03 20:54:08", updated_at: "2009-09-10 20:27:25", image_file_name: "Screen_shot_2009-09-10_at_3.16.59_PM.png", image_content_type: "image/png", image_file_size: 79386>

Does anyone have any idea what the default sort order is? Should I create a default_scope with an :order => :id? I'm not even sure how to reproduce this behaviour on my development machine.

Answer 1

The above answers are not exactly true. According to http://guides.rubyonrails.org/active_record_querying.html 'first' will return the first record, by default sorted by primary key in ascending order.

That being said, I have experienced, this is not always the case in postgresql, when using complex queries. For instance if you sort it before hand or have default scopes.

Cat.order('id desc').first

Then it will not be by ascending order. Also if your model is scoped to another model

Cat.families.first

The can also change the default order.

Answer 2

From the docs:

"You can pass in all the same arguments to this method as you can to find(:first)"

I would recommend ordering by created_at, though not id, like so:

Package.first(:order => :created_at)

Answer 3

SQL doesn't make any guarantees when it comes to the order in which records are retrieved (unless, of course, the ORDER BY keyword is given).