Hey all,
I’m rather new to Ruby and Rails (and not great with SQL), but I’m
developing a ride sharing app and would like to be able to sort on
something I don’t have stored.
I have users, events, and rides, each of which has a zip code. Events
have_many rides, and rides belong_to events.
When an event is selected, I’d like to be able to show a list of rides
to that event, sorted by distance from the logged-in user.
What are some ways to do that? Here’s what I can think of:
- Make a new find_and_sort method that adds a new @distance member
element and sorts the new collection. Would something like this work?
def find_and_sort(event_id)
@rides = Ride.find(:all, :conditions => {“event_id = ?”, event_id})"
for ride in @rides
ride.newdistance = distance_between_zips(session[:user].zip_code,
Event.find(event_id).zip_code);
end
uhm… sort @rides by newdistance
end
What if I want to also remove items from @rides before they are
displayed if that newdistance is too large or some other condition?
uhm… I’m stumped, I guess. That’s why I’m here. 
Many thanks,
Chris
Chris S. wrote:
to that event, sorted by distance from the logged-in user.
Event.find(event_id).zip_code);
end
uhm… sort @rides by newdistance
end
What if I want to also remove items from @rides before they are
displayed if that newdistance is too large or some other condition?
uhm… I’m stumped, I guess. That’s why I’m here. 
OK. Can’t do that.
But I should be able to overload <=>
So in my ride model, could I do this?
def self.<=>(other)
distance_between_zips(session[:user].zip_code, self.zip_code)
<=> distance_between_zips(session[:user].zip_code, other.zip_code)
end
Except… wow. Calling sort on the list means like n*log(n) comparisons,
and each compare calls the distance function twice, and each of those
has five trig functions… so a list of 100 rides would take 2000 trig
calls. Easy peasy!
Oh… do ActiveRecord objects mixin Comparable?
Comments please!
Chris S
Hello Chris !
2006/3/21, Chris S. [email protected]:
def find_and_sort(event_id)
@rides = Ride.find(:all, :conditions => {“event_id = ?”, event_id})"
for ride in @rides
ride.newdistance = distance_between_zips(session[:user].zip_code,
Event.find(event_id).zip_code);
end
uhm… sort @rides by newdistance
end
@rides is an Array, and Array mixes in Enumerable. See #sort_by:
http://www.ruby-doc.org/core/classes/Enumerable.html#M002092
Hope that helps !
