Rails - Jan 2006 - Single Table Inheritance (this is my 3rd post :( )

Hi Everyone,

I hope I get some feedback on my question. Here it goes.

I have a situation here, I have a company table and then using Single 
Table inheritance it is of 3 types:

class Company < ActiveRecord::Base
end

class Vendor < Company
end

class Customer < Company
end

class Agent < Company
end

Now I have a active record Association

class QuoteSheet < ActiveRecord::Base
belongs_to :customer
has_many :vendors
has_one :Agent
end

Now in the table quote_sheets should I use vendor_id, customer_id, 
agent_id or just company_id since all of them are in 1 table called 
companies.

I have read agile wweb development with rail, and no where it says about 
relationship like this.

Thanks
with best regards,
Vikrant

Vikrant Rathore wrote:
> class QuoteSheet < ActiveRecord::Base
> belongs_to :customer
> has_many :vendors
> has_one :Agent
> end
> 
> Now in the table quote_sheets should I use vendor_id, customer_id,
> agent_id or just company_id since all of them are in 1 table called
> companies.
> 
Yeah, it is a bit unclear, but this is what I would try...

class Quotesheet
  belongs_to :customer, :foreign_key=>''customer_id''

...

class Customer
  has_many :quote_sheets, :foreign_key +> ''customer_id''
...

Since you are using belongs_to/has_many I assume you don''t really want
a
HABTM, which is the only reason you would need the
''quote_sheets'' table.

_Kevin

-- 
Posted via http://www.ruby-forum.com/.

Vikrant Rathore wrote:
> Hi Everyone,
> 
> I hope I get some feedback on my question. Here it goes.
> 
> I have a situation here, I have a company table and then using Single 
> Table inheritance it is of 3 types:
> 
> class Company < ActiveRecord::Base
> end
> 
> class Vendor < Company
> end
> 
> class Customer < Company
> end
> 
> class Agent < Company
> end
> 
> Now I have a active record Association
> 
> class QuoteSheet < ActiveRecord::Base
> belongs_to :customer
> has_many :vendors
> has_one :Agent
> end
Without knowing all the details I can''t be sure, but my first
impression
is that vendor, customer and agent are roles rather than types. Could 
the same Company be a vendor with respect to one QuoteSheet, and a 
customer with respect to another? If you use subclasses in the way you 
suggest, this wouldn''t be possible.

I think your associations need a little attention:

belongs_to :customer looks fine - so a customer would be able to have 
many QuoteSheets

has_many :vendors looks wrong - that would mean a vendor would belong to 
  one QuoteSheet - I think it should be has_and_belongs_to_many

has_one :agent (not :Agent) looks wrong - that would mean an agent would 
belong to one QuoteSheet - it should be belongs_to (which really means 
refers_to)

QuoteSheet might look something like:

class QuoteSheet < ActiveRecord::Base

   belongs_to :customer,
              :class_name => "Company",
              :foreign_key => "customer_id"

   belongs_to :agent,
              :class_name => "Company",
              :foreign_key => "agent_id"

   has_and_belongs_to_many :vendors,
              :class_name => "Company",
              :join_table => "quote_sheets_vendors"

end

(absolutely untested!)

You would have to think about how to name the other ends of the 
associations, i.e. the collection of QuoteSheets received as a customer, 
the collection of QuoteSheets issued as an agent, and the collection of 
QuoteSheets quoted on as a vendor.

Is there a bit of model missing here - the actual quote from each vendor?

HTH

   Justin

Hi Justin and Kevin,

Thanks for your response. This is just an illustration of the problem 
indeed the actual DB design includes over 50 tables and different since 
this application is for a large Supply Chain Management (in 
commodities). Currently we have an .net based system with 150 tables and 
another 2 systems based on J2EE with over 200 tables. I was able to 
squeeze all these into little over 50 tables.

Now I want to build a solution on one top of the other. But then stuck 
at the single inheritance problem. But it seems your suggested method 
might work in which i specify the foreign key.

Thanks
with best regards
Vikrant


Justin Forder wrote:
> Vikrant Rathore wrote:
>> Hi Everyone,
>>
>> I hope I get some feedback on my question. Here it goes.
>>
>> I have a situation here, I have a company table and then using Single 
>> Table inheritance it is of 3 types:
>>
>> class Company < ActiveRecord::Base
>> end
>>
>> class Vendor < Company
>> end
>>
>> class Customer < Company
>> end
>>
>> class Agent < Company
>> end
>>
>> Now I have a active record Association
>>
>> class QuoteSheet < ActiveRecord::Base
>> belongs_to :customer
>> has_many :vendors
>> has_one :Agent
>> end
> 
> Without knowing all the details I can''t be sure, but my first
impression
> is that vendor, customer and agent are roles rather than types. Could 
> the same Company be a vendor with respect to one QuoteSheet, and a 
> customer with respect to another? If you use subclasses in the way you 
> suggest, this wouldn''t be possible.
> 
> I think your associations need a little attention:
> 
> belongs_to :customer looks fine - so a customer would be able to have 
> many QuoteSheets
> 
> has_many :vendors looks wrong - that would mean a vendor would belong to 
>  one QuoteSheet - I think it should be has_and_belongs_to_many
> 
> has_one :agent (not :Agent) looks wrong - that would mean an agent would 
> belong to one QuoteSheet - it should be belongs_to (which really means 
> refers_to)
> 
> QuoteSheet might look something like:
> 
> class QuoteSheet < ActiveRecord::Base
> 
>   belongs_to :customer,
>              :class_name => "Company",
>              :foreign_key => "customer_id"
> 
>   belongs_to :agent,
>              :class_name => "Company",
>              :foreign_key => "agent_id"
> 
>   has_and_belongs_to_many :vendors,
>              :class_name => "Company",
>              :join_table => "quote_sheets_vendors"
> 
> end
> 
> (absolutely untested!)
> 
> You would have to think about how to name the other ends of the 
> associations, i.e. the collection of QuoteSheets received as a customer, 
> the collection of QuoteSheets issued as an agent, and the collection of 
> QuoteSheets quoted on as a vendor.
> 
> Is there a bit of model missing here - the actual quote from each vendor?
> 
> HTH
> 
>   Justin

Mailing Lists wrote:
> Hi Justin and Kevin,
> 
> Thanks for your response. This is just an illustration of the problem 
> indeed the actual DB design includes over 50 tables and different since 
> this application is for a large Supply Chain Management (in 
> commodities). Currently we have an .net based system with 150 tables and 
> another 2 systems based on J2EE with over 200 tables. I was able to 
> squeeze all these into little over 50 tables.
> 
> Now I want to build a solution on one top of the other. But then stuck 
> at the single inheritance problem. But it seems your suggested method 
> might work in which i specify the foreign key.
In case it wasn''t clear, I was suggesting that you shouldn''t
use
inheritance - just use Company in multiple roles.

Good luck!

   Justin