Question

This should be a simple problem, but I just can’t seem to find a good solution. I have a list of id’s that the user is selecting, and I want to preserve that order for the foos.

foo_ids = [1899, 7, 1, 2, 3, 42]

foos = Foo.find(foo_ids)

Any ideas on how to either preserve the order on select, or resort after the result set is returned?

Answer 1

I don’t think there is a way to do that with ActiveRecord.

However, here is what I would do:

people_ids = [1899, 7, 2, 3, 42]

people = Person.unscoped.find(people_ids)

people_ids.each_with_object(result = []) do |id, result|
  result << people.detect { person.id == id }
end  

result # => what you are looking for

I use Person.unscoped because in any case, your default scope is not the one you want. So it may be a little (very little) bit faster.

Using find(people_ids) produce only one query no matter how big is people_ids.
The worst would be to do something like this:

people_ids.each_with_object(result = []) do |id, result|
  result << Person.find(id)
end

Because it produces a query for every id.

Sorry not to have the perfect answer 😉