Class Table Inheritance

rubyonrails-talk
1

I'm trying to find a solution to this modeling problem I'm having in Rails, mainly because of the lack of support for ClassTI in Rails.

I'm building a highly complex CMS which will be handling different types of content groups (objects) which each have their own unique set of attributes. For example:

class Product < ActiveRecord::Base; end

class Game < Product; end; class Movie < Product; end; class Car < Product; end;

Normally this can be handled fine by STI but each model has a very unique set of attributes.

product attributes: - id - title - description - created_on - updated_on

game attributes: - id - title [inherited] - description [inherited] - esrb_rating_id - game_platform_id - created_on [inherited] - updated_on [inherited]

movie attributes: - id - title [inherited] - description [inherited] - mpaa_rating_id - production_studio_id - created_on [inherited] - updated_on [inherited]

car attributes: - id - title [inherited] - description [inherited] - mpg_city - mpg_highway - created_on [inherited] - updated_on [inherited]

Can anyone suggest a good solution for me that will allow me to still keep a DRY environment?

2

The first thing that pops into my head as I’m getting ready to walk out the door is:

Create an extra table for each of those sub-types that will use a has_one, belongs_to type of relationship with the STI table, keeping only the extra attributes that are specialized in the extra tables.

In the end, you’d end up with something like c = Car.find(id) c.title == ‘Blah’ c.car_attributes.mpg_city == 24

It seems a little less than perfect, but it’s the only thing I can think of in 3 minutes that will work.

3

Rick M. wrote:

I'm trying to find a solution to this modeling problem I'm having in Rails, mainly because of the lack of support for ClassTI in Rails.

I'm building a highly complex CMS which will be handling different types of content groups (objects) which each have their own unique set of attributes. For example:

class Product < ActiveRecord::Base; end

class Game < Product; end; class Movie < Product; end; class Car < Product; end;

Normally this can be handled fine by STI but each model has a very unique set of attributes.

product attributes: - id - title - description - created_on - updated_on

game attributes: - id - title [inherited] - description [inherited] - esrb_rating_id - game_platform_id - created_on [inherited] - updated_on [inherited]

movie attributes: - id - title [inherited] - description [inherited] - mpaa_rating_id - production_studio_id - created_on [inherited] - updated_on [inherited]

car attributes: - id - title [inherited] - description [inherited] - mpg_city - mpg_highway - created_on [inherited] - updated_on [inherited]

Can anyone suggest a good solution for me that will allow me to still keep a DRY environment?

Yes. Switch to PostgreSQL and use Class Table Inheritance plugin from svn://rubyforge.org/var/svn/clti/