Is it suitable using STI?

Rails
1

I have problems on a simple design problem.
I have many companies. Each company have one or more commercial
activity.
Activities types are: ecommerce, local unit, television, automatic
vending machines, and so on.
Company may have one or more ecommerce activity or one or more local
unit activity, one ormore vending machines, etc.
How can I model this scenario?
Company has_many ecommerce has_many local_units has_many televisions and
so on?

2

On Thu, May 10, 2012 at 10:57 AM, Mauro [email protected] wrote:

I have problems on a simple design problem.
I have many companies. Each company have one or more commercial activity.
Activities types are: ecommerce, local unit, television, automatic
vending machines, and so on.

So can each Company have many CommercialActivities

Then… CommercialActivity is STI, which means it has a type column and
sub-types can be ECommerceActivity, TelevisionActivity, etc…

The only warning is that if each type is dramatically different, you
might
want to investigate doing it with multiple tables so you dont have a lot
of
redundant fields trying model things with additional attributes that
aren’t
shared.

I think this post might help you

–
Greg A.
http://twitter.com/akinsgre

3

On 10 May 2012 16:05, Greg A. [email protected] wrote:

So can each Company have many CommercialActivities

You can also use a project of mine (Super STI) to help you. It helps you
use STI in Rails while keeping your database clean. Read about it at
GitHub - iHiD/super_sti: Add extra data to SDI models yet maintain clean database tables. and
http://www.ihid.co.uk/projects/super_sti

Message me off-list if you want some help with using it.

4

On 10 May 2012 16:26, Mauro [email protected] wrote:

redundant fields trying model things with additional attributes that
aren’t
shared.

Yes the problem is that television, ecommerce, etc. they don’t share
the same attributes.

Use a polymorphic link table.

So tables:
companies: (name:string)
company_activities: (company_id:int, activity_id:int,
activity_type:string)
television_activities(…)
ecommerce_activitiies(…)

Models:
class Company < ActiveRecord::Base
has_many :company_activities
has_many :activities, through: company_activities
end

class CompanyActivity < ActiveRecord::Base
belongs_to :company
belongs_to :activity, polymorphic:true
end

and then lots of:

class TelevisionActivity < ActiveRecord::Base
has_many :company_activities
has_many :companies, through: company_activities
end

class EcommerceActivity < ActiveRecord::Base
has_many :company_activities
has_many :companies, through: company_activities
end

etc

Those could all inherit from Activity if you want to use STI, but they
don’t need to.

5

On 10 May 2012 17:05, Greg A. [email protected] wrote:

So can each Company have many CommercialActivities

Then… CommercialActivity is STI, which means it has a type column and
sub-types can be ECommerceActivity, TelevisionActivity, etc…

The only warning is that if each type is dramatically different, you might
want to investigate doing it with multiple tables so you dont have a lot of
redundant fields trying model things with additional attributes that aren’t
shared.

Yes the problem is that television, ecommerce, etc. they don’t share
the same attributes.

6

On 11 May 2012 09:12, Mauro [email protected] wrote:

Sorry for my ignorance, in your example have you forgot Activity model
and activities table?

ok, sorry they don’t need.

7

Sorry for my ignorance, in your example have you forgot Activity model
and activities table?