Comments on: Multiple Table Inheritance with ActiveRecord

By: John York

John York — Sat, 10 Jul 2010 18:32:13 +0000

Eric, I just had the same problem, and it was because my table wasn't defined properly. the product_properties table must have at least the following columns:

id sellable_type sellable_id

By: Anthony Green

Anthony Green — Sat, 26 Jun 2010 12:28:51 +0000

I’ve been using the same pattern as Ron. I prefer using delegate over method_missing to avoid too much metamagic obviscation.

By: Phillip

Phillip — Mon, 21 Jun 2010 14:39:31 +0000

Hi, this is really a nice approach!

Did you thought about including dynamic finders ? If you just send them to the product_properties class you will get a product_properties object as return and not, as you may want, a pen or a tee object with all the necessary data. Maybe you have something in mind i haven't thought of yet.

thanks anyway for your sharing.

By: Bryan L

Bryan L — Mon, 21 Jun 2010 11:57:07 +0000

This has been extremely helpful to me. One issue I've got is that I can't do eager loading with this. I get this error:

Can not eagerly load the polymorphic association :sellable

Would anyone know how to modify it so that we can do eager loading? I would like to reduce the N+1 queries. Thanks!

By: Evgeniy Dolzhenko

Evgeniy Dolzhenko — Fri, 18 Jun 2010 05:31:43 +0000

Something that burned me a few times ago:

public_methods.include?(meth.to_s)

won't work on 1.9 since method names would be returned as array of symbols instead of an array of strings

public_methods.map(&:to_sym).include?(meth.to_sym)

should work across different versions I think.

By: Eric Coulthard

Eric Coulthard — Thu, 10 Jun 2010 10:08:15 +0000

Would you be able to add which files the code would go in and their path in the rails directory structure? I am trying to recreate what you have done for my project and I cannot since when I try to 'rake db:seed' it tells me that acts_as_product is undefined. If I replace the call with 'include Sellable' I get 'undefined method sellable_type=...'

I am new at this so any help you could give would be greatly appreciated.

By: Ron

Ron — Sun, 16 May 2010 04:01:29 +0000

I'm using a slightly different technique. I think it's roughly similar, but it goes something like:

class Product < ActiveRecord::Base self.abstract_class = true has_one :product_properties, :as => :product, :dependent => :destroy delegate :price, :price=, :name, :name=, :description, :description=, :to => :product_properties def product_properties_with_autobuild product_properties_without_autobuild || build_product_properties end alias_method_chain :product_properties, :autobuild end

Then just inherit your products from Product.

This mostly works in rails 3, but isn't perfect. I've been waiting for a decent CTI implementation for activerecord for years. I have a project that relies on it very heavily. Anyone know of an ORM that supports it properly? Can DataMapper do it?

By: Bruno Pinto

Bruno Pinto — Thu, 29 Apr 2010 02:34:08 +0000

@hakunin

First, thank you so much, this is the best post I have ever seen about MTI on rails.

However, I had one problem when using :include.

Example: class Pen < ActiveRecord::Base include Sellable end

class Pack belongs_to :pen

named_scope :with_product_properties, :include => { :pen => { product_properties => title } end

So, if I try to use @pack = Pack.with_product_properties @pack.pen.title it says that title is an unknown property for this 'aggregation however @pack.pen.product_properties.title is okay.

If you need more info, I could create a code to reproduce this error.

Thanks in advance!

By: Bryan L.

Bryan L. — Thu, 22 Apr 2010 04:02:41 +0000

Bummer, nevermind. Just after posting the previous comment, I figured you can just do “p.sellable.color” and it’ll work fine. How dumb of me.

By: Bryan L.

Bryan L. — Thu, 22 Apr 2010 03:59:35 +0000

Thanks a lot for sharing this code! I've been interested in MTI in Rails for quite some time.

Is it possible to modify the code a little so that it supports something like:

@productproperties = ProductProperties.all @productproperties.each do |p| print p.tee.color end

This would be extremely useful. Thanks.