order by association

Question

Here are my models.

Restaurant has many patrons
patrons have many transactions

In controller index all patrons like

@pts = Restaurant.find(1).patrons

and in view I simply list the patrons attributes, inluding number of transaction per patrons like <% @pts.each do |p| <%= p.transactions.count %>

How would I order the resultset (@pts) by transaction count of each patron?

Thanks

Answer 1

This will order by id. Put it in the model.

  has_many :patrons, :order => "id DESC"

Answer 2

Assuming you don't have too many patrons and you don't use a count cache (transactions_counter), you could do it like this:

@pt.sort_by{|p|p.transactions.count}.each do |patron|
...

Or you could set up a counter cache and do it in sql(you can do it without but the queries are a bit more annoying)

add transactions_counter to the patrons table and

class Patron < ActiveRecord::Base
  has_many :transactions, :counter_cache => true
  #...
end

Then you can sort by it in your query:

@pts = Restaurant.find(1).patrons.all :order => "patrons.transactions_counter DESC"

You could even add that to your has_many call and simplify things.