Rails - Sep 2005 - nested DB relationship

Hello,

  I have a situation as follows in a DB relationship.

Manufacturers ==>  ID / Name
Models ==> ID / Name / Manufacturer_id

Nodes  ==> ID / Name / Model_ID

  I am setting up an inventory where each node is a certain type of 
manufacturer/model.  One manufacturer can have many models.  So in my 
nodes database I only put a relationship to the model_id, since from the 
model_id i can determine the Manufacturer.  What is the best way to code 
this in say a form ?

What i want is say, when a user changes the Manufacturer in a "New Node 
Form", i find all the models for that manufacturer in a dropdown in the 
new.rhtml form.. Is there a way to handle this in the model definition 
somehow automatically ?

thanks
adam

On 15.9.2005, at 18.55, Adam Denenberg wrote:
> Hello,
>
>  I have a situation as follows in a DB relationship.
>
> Manufacturers ==>  ID / Name
> Models ==> ID / Name / Manufacturer_id
>
> Nodes  ==> ID / Name / Model_ID
>
>  I am setting up an inventory where each node is a certain type of  
> manufacturer/model.  One manufacturer can have many models.  So in  
> my nodes database I only put a relationship to the model_id, since  
> from the model_id i can determine the Manufacturer.  What is the  
> best way to code this in say a form ?
>
> What i want is say, when a user changes the Manufacturer in a "New  
> Node Form", i find all the models for that manufacturer in a  
> dropdown in the new.rhtml form.. Is there a way to handle this in  
> the model definition somehow automatically ?
Adam,

This is just a presentation problem if you have your database setup  
as above and ActiveRecord accordingly:

Manufacturer has_many :models

Model belongs_to :manufacturer
             has_many :nodes

Node belongs_to :model

Now you can put a select dropdown for manufacturers to the form and  
use AJAX to bring another dropdown with the models to the page when a  
manufacturer is selected. You can use e.g. observe_field helper [1]  
for that or put the "new Ajax.updater" javascript call in an event  
handler [2] of the first field.

//jarkko


[1] http://rails.rubyonrails.com/classes/ActionView/Helpers/ 
JavaScriptHelper.html#M000402
[2] like onChange: http://www.devguru.com/Technologies/ecmascript/ 
quickref/evhan_onchange.html
>
> thanks
> adam
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