Question

I have 2 models, User and Purchase.
A User has_many :purchases and a Purchase belongs_to :user

Purchases fields are:

id, product_id, user_id, amount, created_at

What I am trying to achieve is a method call such as:
User.top_five which would return the 5 Users with the highest purchase value, i.e. the sum of the purchases.amount field for each user.

I also want to be able to do something like User.top_five(:start_date=>'01/01/2010',:end_date=>'31/12/2010') , i.e. select a time period to calculate the top five users.

So I’ve been trying to get the right combination of joins, sums, order_bys etc, but I’m just not getting it. So hopefully someone can point me in the right direction!
Hopefully I’ve given enough info here, this is my first question.

thanks

Answer 1

I suggest something like

def self.top_five(start_date, end_date)
  User.all(:select => "users.*, SUM(purchased.amount) as purchased_sum",
           :joins => "LEFT JOIN purchases AS purchased ON purchased.user_id = users.id",
           :group => "users.id",
           :conditions => ["purchased.created_at BETWEEN ? AND ?", start_date, end_date],
           :order => "purchased_sum DESC",
           :limit => 5)
end