Rails - Feb 2007 - Polymorphic either or but not both

I am trying to create a generic person model. Then subclass it as
either a professor or an author. The only problem is that since some
professors are authors, I don''t want duplicate entries. Any ideas on
how to handle this?


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I wouldn''t use a polymorphic model for this, I would use single table
inheritance.

Have a single table People with a type column, then have a model Person and
subclasses for each type so:

class Person < ActiveRecord::Base
end

class Professor < Person
end

class Author < Person
end


On 2/6/07, wbsmith83-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
<wbsmith83-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
>
> I am trying to create a generic person model. Then subclass it as
> either a professor or an author. The only problem is that since some
> professors are authors, I don''t want duplicate entries. Any ideas
on
> how to handle this?
>
>
> >
>
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I just went back and re-read your original post, single table won''t
work either since you have the possibility of a person having two
types.

The solution is going to be a little more complex as you will need to
create a many to many relationship.

I would use 3 tables:

    create_table :people do |t|
      t.column :id, :integer
      t.column :name, :string
    end

    create_table :person_roles do |t|
      t.column :id, :integer
      t.column :person_id, :integer
      t.column :role_id, :integer
    end

    create_table :people do |t|
      t.column :id, :integer
      t.column :role, :string
    end

"People" would house the information about the person,
"Roles" would
be a domain of roles a person could play (Author, professor, student),
and "Person_Roles" would allow the many to many.

You would then have:

class Person < ActiveRecord::Base
  has_many :roles, :through => :person_roles
  has_many :person_roles
end


Hope that helps, sorry for my hasty first post!

Joe


On Feb 6, 9:08 am, "Joe Cairns"
<joe.cai...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I wouldn''t use a polymorphic model for this, I would use single
table
> inheritance.
>
> Have a single table People with a type column, then have a model Person and
> subclasses for each type so:
>
> class Person < ActiveRecord::Base
> end
>
> class Professor < Person
> end
>
> class Author < Person
> end
>
> On 2/6/07, wbsmit...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
<wbsmit...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> > I am trying to create a generic person model. Then subclass it as
> > either a professor or an author. The only problem is that since some
> > professors are authors, I don''t want duplicate entries. Any
ideas on
> > how to handle this?

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I should know never to post prior to my morning caffeine intake... There is
a typo on the third table definition:
>   create_table :people do |t|
>      t.column :id, :integer
>      t.column :role, :string
>    end


Should be:
  create_table :roles do |t|
     t.column :id, :integer
     t.column :role, :string
   end



On 2/6/07, Ruby Joe <joe.cairns-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
>
> I just went back and re-read your original post, single table
won''t
> work either since you have the possibility of a person having two
> types.
>
> The solution is going to be a little more complex as you will need to
> create a many to many relationship.
>
> I would use 3 tables:
>
>     create_table :people do |t|
>       t.column :id, :integer
>       t.column :name, :string
>     end
>
>     create_table :person_roles do |t|
>       t.column :id, :integer
>       t.column :person_id, :integer
>       t.column :role_id, :integer
>     end
>
>     create_table :people do |t|
>       t.column :id, :integer
>       t.column :role, :string
>     end
>
> "People" would house the information about the person,
"Roles" would
> be a domain of roles a person could play (Author, professor, student),
> and "Person_Roles" would allow the many to many.
>
> You would then have:
>
> class Person < ActiveRecord::Base
>   has_many :roles, :through => :person_roles
>   has_many :person_roles
> end
>
>
> Hope that helps, sorry for my hasty first post!
>
> Joe
>
>
> On Feb 6, 9:08 am, "Joe Cairns"
<joe.cai...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > I wouldn''t use a polymorphic model for this, I would use
single table
> > inheritance.
> >
> > Have a single table People with a type column, then have a model
Person
> and
> > subclasses for each type so:
> >
> > class Person < ActiveRecord::Base
> > end
> >
> > class Professor < Person
> > end
> >
> > class Author < Person
> > end
> >
> > On 2/6/07, wbsmit...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
<wbsmit...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >
> >
> >
> > > I am trying to create a generic person model. Then subclass it as
> > > either a professor or an author. The only problem is that since
some
> > > professors are authors, I don''t want duplicate entries.
Any ideas on
> > > how to handle this?
>
>
> >
>
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