From: harm.hoekstra@...
Date: 2006-11-27T04:50:06+09:00
Subject: RoR: model on basis of a view on a LEFT JOIN?

Hi,

I want to make a RoR webapp and on one screen the user should see
products and his/her own rating:

   PRODUCT       YOUR RATING
   product100       <no rating yet, add rating widget>
   product101       ****
   product102       **
   product103       <no rating yet, add rating widget>
    ...

So I have a listing over products, but I need to join in the ratings of
the current user (not of other users).

I think there are 2 approaches:

A. Add a getter method to the model to get the rating (filtered on
current user)
B. Make a view from SELECT * from products LEFT JOIN ratings ON
products.id = ratings.product_id AND
     ratings.user_id = {user.id}

I guess method A will result in 20 queries being fired when a list of
20 are shown. Not that the webapp will have heavy traffic, but its a
more clean approach if the database does the heavy lifting in one
swoop, I think.

So I incline to B, but are there any pitalls when making a activerecord
model on basis of a VIEW ?

Or perhaps even better solutions are already thought out in Rails.

Thanks in advance,

Harm