Rails多态协会的问题

Question

I'm trying to create an app for users to create a list of watches they own or wish to buy. I want users to be able to describe a lot of detail/attributes about their watches. I'm trying to create a parent/child association, but not using STI, as the children models have different data and I don't want a bunch of null values in my table.

I have 4 tables:

• users
  • Some user attributes
• watches
  • user_id
  • A bunch of attributes that are common to all watches, name, brand etc.
  • content_id
  • content_type
• mechanical_watches
  • Some attributes that only apply to mechanical watches
• quartz_watches
  • some attributes that only apply to quartz watches

Models

class User < ApplicationRecord
 include Clearance::User

 has_many :watches
end

class Watch < ApplicationRecord
 belongs_to :user
 belongs_to :content, polymorphic: true
end

class MechanicalWatch < Watch
 has_one :watch, as: :content
end

class QuartzWatch < Watch
 has_one :watch, as: :content
end

I'm not a 100% sure if I've setup the associations correctly. But the problem I'm having is that when I enter MechanicalWatch into the console it returns only the attributes on Watch not any of the attributes in the mechanical_watches table. I've tried everything I can think of. Any thoughts as to what I'm doing wrong.

I'm using Rails 5, Ruby 2.3.1, and Postgres for the db.

Answer 1

I don't think you want inheritance on MechanicalWatch or QuartzWatch . They appear to be separate tables from Watch . The relationship you show is MechanicalWatch "has a" Watch , instead of MechanicalWatch "is a" Watch .

You would change

class MechanicalWatch < Watch

to

class MechanicalWatch

Answer 2

From what I understand you want to be able to create a mechanical_watch instance, but still have the ability to set the fields on the watch model.

Ie MechanicalWatch.new.field_on_watch = 4

If that's correct then u can look at this:

http://api.rubyonrails.org/classes/Module.html

The pattern your looking for is delegation.

An important question to ask though: do you plan to use watches in a polymorphic way. Ie Will u show all types of watches on the same page? Or will different watches be displayed separately?