Rails - May 2007 - CTI in ActiveRecord

I search an plugin or gem, but don''t find nothing satisfactory. I
believe to be stranger a technology that nails the DRY, have that create
you vary equal tables, instead of using inheritance.

Exists an soluction for this? I want a solution similar to this:


create_table :people |t| do
   t.column :name
   t.column :address
end

create_table :customer |t| do
   t.column :person_id
   t.column :cpf
end

create_table :employee |t| do
   t.column :person_id
   t.column :wage
end


class Person < ActiveRecord::Base
end

clas Customer < Person
end

class Employee < Person
end




Cusotmer.name
Customer.cpf

Employee.name
Employee.wage

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To my knowledge rails only supports STI or separate tables for each
subclass.  If you make People abstract then each subclass will be in
its own tale.

The hybrid you show is not directly supported.  You would need to
model them as associated tables.  But, if you think about it that
makes sense.  How would you expect a row in the employee table to
connect to a row in the people table?  The best way is to add a
people_id to employee.  That becomes a :belongs_to and you are all
set.  You can always add support in Employee for delegating to the
associated people object so to the user they appear to be subclasses.

Michael


On May 28, 12:06 pm, Marcelo Junior
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
> I search an plugin or gem, but don''t find nothing satisfactory. I
> believe to be stranger a technology that nails the DRY, have that create
> you vary equal tables, instead of using inheritance.
>
> Exists an soluction for this? I want a solution similar to this:
>
> create_table :people |t| do
>    t.column :name
>    t.column :address
> end
>
> create_table :customer |t| do
>    t.column :person_id
>    t.column :cpf
> end
>
> create_table :employee |t| do
>    t.column :person_id
>    t.column :wage
> end
>
> class Person < ActiveRecord::Base
> end
>
> clas Customer < Person
> end
>
> class Employee < Person
> end
>
> Cusotmer.name
> Customer.cpf
>
> Employee.name
> Employee.wage
>
> --
> Posted viahttp://www.ruby-forum.com/.

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MichaelLatta wrote:
> To my knowledge rails only supports STI or separate tables for each
> subclass.  If you make People abstract then each subclass will be in
> its own tale.
> 
> The hybrid you show is not directly supported.  You would need to
> model them as associated tables.  But, if you think about it that
> makes sense.  How would you expect a row in the employee table to
> connect to a row in the people table?  The best way is to add a
> people_id to employee.  That becomes a :belongs_to and you are all
> set.  You can always add support in Employee for delegating to the
> associated people object so to the user they appear to be subclasses.
> 
> Michael

This is not inheritance, but relationship. What I want inheritance.

Some plugin or gem?

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CTI = DRY


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In Rails you can use STI very easily. The following example should
clearify things (from Agile Web Development with Rails, you should buy
the book at http://www.pragmaticprogrammer.com/ ):

create_table :people, :force => true do |t|
  t.column :type, :string

  # common attributes
  t.column :name, :string
  t.column :email, :string

  # attributes for type=Customer
  t.column :balance, :decimal, :precision => 10, :scale => 2

  # attributes for type=Employee
  t.column :reports_to, :integer
  t.column :dept, :integer

  # attributes for type=Manager
  # - none -
end


class Person < ActiveRecord::Base
end

class Customer < Person
end

class Employee < Person
  belongs_to :boss, :class_name => "Employee" , :foreign_key
=> :reports_to
end

class Manager < Employee
end

Customer.create(:name => ''John Doe'' , :email =>
"john-Ch9RrZxMC0c@public.gmane.org" , :balance => 78.29)
wilma = Manager.create(:name => ''Wilma Flint'' , :email
=>
"wilma-d1FEnVXDQDs@public.gmane.org" ,:dept => 23)
Customer.create(:name => ''Bert Public'' , :email =>
"b@public.net" ,:balance => 12.45)
barney = Employee.new(:name => ''Barney Rub'' , :email =>
"barney-d1FEnVXDQDs@public.gmane.org" ,:dept => 23)
barney.boss = wilma
barney.save!

manager = Person.find_by_name("Wilma Flint" )
puts manager.class #=> Manager
puts manager.email #=> wilma-d1FEnVXDQDs@public.gmane.org
puts manager.dept #=> 23

customer = Person.find_by_name("Bert Public" )
puts customer.class #=> Customer
puts customer.email #=> b@public.net
puts customer.balance #=> 12.45

Regards,
Bas


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Marcelo Junior wrote:
> I search an plugin or gem, but don''t find nothing satisfactory. I
> believe to be stranger a technology that nails the DRY, have that create
> you vary equal tables, instead of using inheritance.
> 
Take a peek at http://clti.rubyforge.org/ . It''s still only for
PostgreSQL though.

--
Sava Chankov


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