'none' for empty result set

[dpisarewski]

It would be great if there were a 'none' method returning empty result set like active_record does it.

http://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-none

[subvertallchris]

I started playing around with this earlier, seems doable. I got it working as a class method but we're going to need to make QueryProxy aware of it, otherwise things will break, and I'm not sure of the best way to do that just yet.

[dpisarewski]

I defined a scope 'none' as a workaround.

scope :none, -> { where('1 = 0') }

[cheerfulstoic]

Interestingly that seems to be just how it's implemented in ActiveRecord ;)

https://github.com/rails/rails/blob/master/activerecord/lib/active_record/relation/query_methods.rb#L692

I didn't know about this extending business. Looks pretty cool. I wonder how new it is

[cheerfulstoic]

Ah, interesting, I guess not quite because the NullRelation introduces a lot:

https://github.com/rails/rails/blob/08754f12e65a9ec79633a605e986d0f1ffa4b251/activerecord/lib/active_record/null_relation.rb

[dpisarewski]

I think, NullRelation is just an optimization that prevents firing database queries or doing unnecessary computations.

[cheerfulstoic]

Ah, that makes sense ;)

Might be simpler to just have some variable state which is propogated down the chain. Maybe that's what @subvertallchris was working on anyway

[subvertallchris]

Yup, that is what I was talking about! The problem with scope :none, -> { where('1 = 0') } is that it's going to query the DB. I think we can avoid it entirely if we can find a clever way to tell it that it's a null object.