Really not much more to tell than what is already in the question.
using mongoid:
People.asc(:age)
I get nil value first.
is there a way to always return nil last, or to tell mongodb to treat nil as very high?
Exactly like what is answered for the same problem in sql here
Not if you want ascending order for the non-nil ages. If that is unimportant, you could see if
People.desc(:age)
will put the nil values at the end. Alternatively, you could try adding a search parameter to not return nil values:
People.not_in(age: [nil]).asc(:age)
I'm pretty sure the answer is "no" for MongoDB. There's no way to supply a custom sorting function, you can only supply the keys to sort on. There is a request for custom sorting functions and they even mention your particular use case:
javascript sort helper for custom sorting / indexing
[...]
Could this be used to sort alphabetically on a field, and put documents with a null value at the end of the result set?
[...]
@nick - yes
So you're not alone in wanting to put null
s at one end or the other.
I think the best you can do right now is to do it in Ruby, something like this:
nils, not_nils = People.asc(:age).partition { |p| p.age.nil? }
people = not_nils + nils
I don't use Mongoid but presumably asc
gives you an Enumerable, if not then perhaps you could stick a to_a
in there. Of course this sort of hackery is useless if you're paginating.
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