Question

I have the following tables

Pedal
  Brand:string
  Classification:string
  Model:string  

Variety
  Title:string
  name:string
  pedal_id:integer

Example
  quality:string
  price:double
  variety_id:integer

I would like to find the average price based on brand, model, and quality. I cannot figure out the way in which I would do this from the Pedal model.

Answer 1

I don’t know if Rails 3.1 actually can do this properly,

but you should just be able to do,

Example.joins(:variety => :pedal)
  .group("pedals.brand, pedals.model, examples.quality")
  .average(:price)