Code Discussions: Modeling ...

## Background class Member < ActiveRecord::Base has_many :readings end class Metric < ActiveRecord::Base has_many :metric_attributes end class MetricAttribute < ActiveRecord::Base belongs_to :metric has_many :readings end class Reading < ActiveRecord::Base belongs_to :member belongs_to :metric_attribute end Example: Metric: Cholesterol MetricAttribute: HDL Member: me Reading: HDL - 64 ## The Problem There is a view in the application where we start with a list of metrics and need to output the latest reading for an attribute and the current user. The initial conversation:

Justin Marney

As I see it there are three ways to get at the reading. I can go from the attribute:


or the member:


or the Reading class:

Reading.for_member_and_attribute(member, attribute)

Assuming some scopeage gets me the latest. That aspect is not my concern ATM, but the things that hangs me up is, which do I choose?

Patrick Reagan
You're looking for the right API, yea?
So yea, what are the tradeoffs, if any, to choosing one over the other? Is there an appropriate choice?
I have 2 opinions -- one of which i can justify and another I cannot.
Is the second one that you can't trust a woman?

3 then. But, I would come from the member:




Based on what you describe, it sounds like getting this reading is a concern of member.

Patrick is development director in Viget's Boulder, CO, office. He writes clean Ruby code and automates system infrastructure for clients such as Shure and Volunteers of America.

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