Hi, I'm using rails 1.2.3 and mysql 5 I have a collection of models like this: Car has_many Passengers; Passenger has_many Pocket_Items ***I want to issue a Car.find command from rails where I find all cars where at least 1 passenger is carrying a knife (or whatever) in his/ her pocket.*** The details are shown below: Table 1: cars (id, license_plate, make, model) Table 2: passengers (id, car_id, first_name, last_name) Table 3: pocket_items (id, passenger_id, item_description) The description of the Car model would be something like this: class Car < ActiveRecord::Base has_many :passengers has_many :pocket_items, :through => :passengers end so, e.g. car # 1 may contain 2 passengers. passenger 1 may have a wallet and a knife, whereas passenger 2 may have a knife and keys. So, now let's say that I want to find all cars where at least 1 passenger is carrying a knife. in SQL, I might issue the following statement select c.id, c.license_plate, c.make, c.model from cars c inner join passengers p on (p.car_id = c.id) inner join pocket_items pi on (pi.passenger_id = p.id) where pi.item_description = 'Knife' this works, except that if a car contains 2 people, each carrying a knife, the same car will be returned on 2 separate rows. obviously, this can be eliminated by changing the statement above to "select distinct ...." My questions are: 1. Is there another (more elegant) way of demanding an INNER JOIN from rails aside from issuing it directly from the :joins option within the find method? 2. Is there a rails idiom for 'deduping' my result set (i.e. I only want a result set of UNIQUE cars from my find query. From the agile development book, ed 2 (page 341), one can 'dedupe' *child* objects using the modifier :uniq => true. However, i'm not sure if there's a way to do this on the *parent* object. 3. are there any (more efficient) approaches to using rails to accomplish the query outlined above? i.e. I want to find all cars where at least 1 passenger carries a knife. thanks!
on 2007-06-10 18:43
on 2007-06-21 15:03
As for "deduping" your result set, have a look here: http://api.rubyonrails.org/classes/ActiveRecord/Ba... You can pass the :select flag to find with something like this -> ":select => 'disctinct cars.*'"