Rails - May 2006 - object class with STI and Polymorphic Assoc''s.

Hi, lets say I have a a table, "Linkings" that I am using for 
polymorphic associations.  One of the associations is to the "person" 
table, and there are several other associations.

"Person" has 2 types, "slacker" and "suckup".

It is modelled as such:
class Linking < ActiveRecord::Base
  belongs_to :person
  belongs_to :linkable, :polymorphic => true
end

class Person < ActiveRecord::Base
  has_many :linkables
end
class Slacker < Person
end
class Yadda < Person
end

I''d like to have one controller for both "slacker" and
"suckup", so I
tried using this:
@linkable.class

If the linkable type is a "Person" I get either "slacker" or
"suckup",
the type of "person".  Is there a way to get the actual linkable type?

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

Joe Cairns wrote:
> Hi, lets say I have a a table, "Linkings" that I am using for 
> polymorphic associations.  One of the associations is to the
"person"
> table, and there are several other associations.
> 
> "Person" has 2 types, "slacker" and "suckup".
> 
> It is modelled as such:
> class Linking < ActiveRecord::Base
>   belongs_to :person
>   belongs_to :linkable, :polymorphic => true
> end
> 
> class Person < ActiveRecord::Base
>   has_many :linkables
> end
> class Slacker < Person
> end
> class Yadda < Person
> end
> 
> I''d like to have one controller for both "slacker" and
"suckup", so I
> tried using this:
> @linkable.class
> 
> If the linkable type is a "Person" I get either
"slacker" or "suckup",
> the type of "person".  Is there a way to get the actual linkable
type?
I''m not sure exactly what you''re trying to do, since you left
out the
table schemas/migrations. I guess you''re confusing STI and polymorphic 
associations. STI lets you use inheritance to put subclasses in the same 
table as their common superclass. Polymorphic associations use a 
composite key to allow a model to be associated by models in several 
other tables. I don''t think you need to combine the two for what
you''re
doing.

If you''re doing a polymorphic has_many in Person, it should go like
  has_many :linkings, :as => :linkable
But you don''t need to do that since the `belongs_to :person`
declaration
works for slackers and yaddas too.

Drop the polymorphism, just use STI. Does that help?

--
Josh Susser
http://blog.hasmanythrough.com

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

On 15 May 2006, at 08:01, Josh Susser wrote:
> Joe Cairns wrote:
>> Hi, lets say I have a a table, "Linkings" that I am using for
>> polymorphic associations.  One of the associations is to the
"person"
>> table, and there are several other associations.
>>
>> "Person" has 2 types, "slacker" and
"suckup".
>>
>> It is modelled as such:
>> class Linking < ActiveRecord::Base
>>   belongs_to :person
>>   belongs_to :linkable, :polymorphic => true
>> end
>>
>> class Person < ActiveRecord::Base
>>   has_many :linkables
>> end
>> class Slacker < Person
>> end
>> class Yadda < Person
>> end
>>
>> I''d like to have one controller for both "slacker"
and "suckup", so I
>> tried using this:
>> @linkable.class
>>
>> If the linkable type is a "Person" I get either
"slacker" or
>> "suckup",
>> the type of "person".  Is there a way to get the actual
linkable
>> type?
>
> I''m not sure exactly what you''re trying to do, since you
left out the
> table schemas/migrations. I guess you''re confusing STI and
polymorphic
> associations. STI lets you use inheritance to put subclasses in the  
> same
> table as their common superclass. Polymorphic associations use a
> composite key to allow a model to be associated by models in several
> other tables. I don''t think you need to combine the two for what  
> you''re
> doing.
>
> If you''re doing a polymorphic has_many in Person, it should go
like
>   has_many :linkings, :as => :linkable
> But you don''t need to do that since the `belongs_to :person`  
> declaration
> works for slackers and yaddas too.
>
> Drop the polymorphism, just use STI. Does that help?
I believe what he wants is the following:
He has a table people and a table companies and a table projects for  
example. A person can be linked to a person, or a company, or a  
project. A company can be linked to a company, a person or a project.  
A project can be linked to another project, a company or a person. So  
basically, you can link anything to anything. In this case, I would  
go for a normal many to many relationship (for the self referential  
one, you can use Rails Recipe n? 18), overriding the defaults of the  
habtm relationship to use that one table which holds the links.


Best regards

Peter De Berdt