Surprising behavior of ActiveRecord order method

[Doug Orleans]

This behavior surprised me, but I can't decide if it's a bug or not:

Loading development environment (Rails 4.0.0.rc1)
2.0.0p0 :001 > p = Post.new

 => #<Post id: nil, title: nil, text: nil, created_at: nil, updated_at: nil> 

2.0.0p0 :002 > p.comments.build


 => #<Comment id: nil, commenter: nil, body: nil, post_id: nil, created_at: nil, updated_at: nil> 


2.0.0p0 :003 > p.comments.size
 => 1 


2.0.0p0 :004 > p.comments.order(:created_at).size


 => 0 



What do you think?



--Doug

[rtwomey]

Hi Doug,

Build doesn't save the comment. The order method is doing a lookup in the db and ordering by whatever criteria you specify. Since there's nothing actually saved, it won't return anything.

Try switching build to create (and passing in whatever params you need), then running it again. The order line should return results.

-Ryan

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[Doug Orleans]

I understand that it only includes persisted objects, but other AR methods (e.g. size) seem to do the right thing and include both persisted and non-persisted. I'm wondering if it's a bug that order doesn't do the right thing here too, or if there should be another method to do what I want it to do.

--Doug

[Brice Stacey]

When you call `order(:created_at)` you're actually creating a new AR Relation and since it hasn't been executed yet it will hit the database. If you want an in memory sort use `sort_by` or be sure to only use a single relation (e.g. don't call p.comments and later p.comments(:created_at). Instead, save `comments = p.comments.order(:created_at)` and use `comments`).