Question

I always wondered how to query and get results that doesn’t fit in a model. Similar how it’s done using LINQ and projecting into anonymous objects.

So here’s the simple schema:

# Product.rb
class Product < ActiveRecord::Base
   has_many :product_views

   # attributes: id, name, description, created_at, updated_at
end

# ProductView.rb
class ProductView < ActiveRecord::Base
   belongs_to :product

   # attributes: id, product_id, request_ip, created_at, updated_at
end

Basically I need to get a list of Products (preferably just id and name) along with the count of views it had. Obviously ordered by view count desc.

This is the SQL I want to get:

select 
    p.id,
    p.name,    
    count(pv.product_id) as views
from 
    product_views pv
inner join
    products p on pv.product_id = p.id
group by
    pv.product_id
order by
    count(product_id) desc

I tried the following and similar, but I’m getting ProductView objects, and I would like to get just an array or whatever.

ProductView.includes(:product)
           .group('product_id')
           .select("products.id, products.name, count(product_id)")

This kind of thing are trivial using plain SQL or LINQ, but I find myself stucked with this kind of queries in Rails. Maybe I’m not thinking in the famous ‘rails way’, maybe I’m missing something obvious.

So how do you do this kind of queries in Rails 3, and specifically this one? Any suggestions to improve the way I’m doing this are welcome.

Thank you

Answer 1

Within a class method in the Product class:

Product.includes(:product_views).all.map { |p| [p.id, p.name, p.product_views.size] }

Then sort it however you want.