Rails - Apr 2006 - belongs_to and has_many

I know this has been rehashed many times, but I don''t get it.
I can''t find it documented to were I understand all the parts. I can 
make this work using Rails database design conventions, but in this case 
I am not able to do that.
    I find examples, but the ones I find do not follow the conventions. 
They also do not give enough information to understand what is going on.

In the model:
   What is the "association"? Is it the field name minus the _id?
   :foreign_key is the key in the other table.
   :class_name is the name of the model of the other table.
------createtables.sql
CREATE TABLE admins(
  id INTEGER PRIMARY KEY,
  admin VARCHAR(32) NOT NULL,
);
CREATE TABLE machines(
  id INTEGER PRIMARY KEY,
  padmin_id REFERENCES admins(admin),
  sadmin_id REFERENCES admins(admin)
)
-------models/machine.rb------------
class Machine < ActiveRecord::Base
  belongs_to :padmin, :class_name => "admin", :foreign_key =>
"id"
  belongs_to :sadmin, :class_name => "admin", :foreign_key =>
"id"
end
-------models/admin.rb--------------
class Admin < ActiveRecord::Base
  has_many :machines, :foreign_key => ''padmin_id''
  has_many :machines, :foreign_key => ''sadmin_id''
end
-------views/_list_stripes.rhtml-----
If it were a straight association machine.admin_id and admin.id, then 
this works
<td><%= list_stripes.admin ? list_stripes.admin["admin"] :
"UnAssigned"
%></td>
-------------------------------------
I would be happy if I could understand it well enough that I could use 
it without the compilcation of "sadmin_id".

Blake


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

I''m not sure i quite understand your data model...

If it''s: "One admin can have many machines, One machine belongs to
many
admins" then you should have a joiner table:

administrators      administrators_machines       machines
--------------      -----------------------       --------
id            <---- administrator_id         |--> id
admin               machine_id             --     machine
--------------      -----------------------       ---------

Your models will then reflect this relationship:

class Machine < ActiveRecord::Base
   has_and_belongs_to_many :administrators
end

class Administrator < ActiveRecord::Base
   has_and_belongs_to_many :machines
end

Rails will automatically map everything together for you.  The 
associations should be avaliable as a collection in the models:

@administrator.machines.find(:all)

Hopefully this will be helpful - i apologise if i''ve mis-understood
your
problem :0)

Steve


Blake Lewis wrote:
>     I know this has been rehashed many times, but I don''t get it.
> I can''t find it documented to were I understand all the parts. I
can
> make this work using Rails database design conventions, but in this case 
> I am not able to do that.
>     I find examples, but the ones I find do not follow the conventions. 
> They also do not give enough information to understand what is going on.
> 
> In the model:
>    What is the "association"? Is it the field name minus the _id?
>    :foreign_key is the key in the other table.
>    :class_name is the name of the model of the other table.
> ------createtables.sql
> CREATE TABLE admins(
>   id INTEGER PRIMARY KEY,
>   admin VARCHAR(32) NOT NULL,
> );
> CREATE TABLE machines(
>   id INTEGER PRIMARY KEY,
>   padmin_id REFERENCES admins(admin),
>   sadmin_id REFERENCES admins(admin)
> )
> -------models/machine.rb------------
> class Machine < ActiveRecord::Base
>   belongs_to :padmin, :class_name => "admin", :foreign_key
=> "id"
>   belongs_to :sadmin, :class_name => "admin", :foreign_key
=> "id"
> end
> -------models/admin.rb--------------
> class Admin < ActiveRecord::Base
>   has_many :machines, :foreign_key => ''padmin_id''
>   has_many :machines, :foreign_key => ''sadmin_id''
> end
> -------views/_list_stripes.rhtml-----
> If it were a straight association machine.admin_id and admin.id, then 
> this works
> <td><%= list_stripes.admin ? list_stripes.admin["admin"]
: "UnAssigned"
> %></td>
> -------------------------------------
> I would be happy if I could understand it well enough that I could use 
> it without the compilcation of "sadmin_id".
> 
> Blake
> 
>

Steve,
    I think you understand my data. I was trying to avoid habtm. I
haven''t found a way to associate data with each join. We have primary
and secondary admins for each machine.

habtm does not deal with this:

administrators      administrators_machines       machines
--------------      -----------------------       --------
id            <---- administrator_id         |--> id
admin               machine_id             --     machine
                    [primary | secondary]
--------------      -----------------------       ---------
    In the mean time I would like to figure out the correct syntax for
describing  the models and listing the data with just belongs_to and
has_many. I would drop the secondary admin out of the model. But instead
of renameing things I would like to know how to do it without following
rails naming conventions.

Does join through allow this type of model?

Blake

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

Blake Lewis wrote:
> Does join through allow this type of model?
> 
> Blake

The :through approach requires creating a new Model in ghe middle, say 
''adminship'',

 so   administrator has_many :adminships and has_many :machines :though 
=> ''adminships''
and  machine has_many :adminships and has_many :administrators :through 
=> ''adminships''.

The adminships table, in addition to administrayor_id and machine_id 
will have, say a priority column indicating primary or secondary

The Adminship model would belongs_to :machine and belongs_to 
:administrator.

More blurb here: 
http://blog.hasmanythrough.com/articles/2006/04/20/many-to-many-dance-off

Does this help ?

Alan

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