Question

Can someone help me understand how to convert this sql query to a named_scope or maybe a method?

Background: A trip can have many trip_runs. I’m trying to be able to say TripRun.upcoming and return only valid runs from valid trips based on the following query

SELECT r.*
FROM trip_run r
LEFT JOIN trips t
ON r.trip_id = t.id
WHERE r.starts_on > NOW()
AND t.is_booked = 1
AND t.is_cancelled IS NULL

thank you

Answer 1

Based on Joshua’s answer, but for rails 2.3:

class Trip < ActiveRecord::Base
  has_many :trip_runs
  named_scope :booked, :conditions => 'is_booked = 1 AND is_cancelled IS NULL'
end

class TripRun < ActiveRecord::Base
  belongs_to :trip
  named_scope :upcoming, :conditions => 'starts_on > NOW()'
end

Trip.booked.trip_runs.upcoming

or alternatively:

class Trip < ActiveRecord::Base
  has_many :trip_runs
end

class TripRun < ActiveRecord::Base
  belongs_to :trip
  named_scope :upcoming,
              :conditions => 'trip.is_booked = 1 AND trip.is_cancelled IS NULL
                              AND trip_runs.starts_on > NOW()', 
              :joins => :trip
end

TripRun.upcoming

That will use an INNER JOIN not a LEFT JOIN, but since you’re looking for rows with trip.is_booked set to a non-null value, the results will be the same and the query will be no slower.