Rails - May 2006 - Adding methods to model based on foreign table rows

Hi all,

I wondered if the following is implemented in ActiveRecord:

I have three tables: "products", "properties" and
"product_properties"

the products table holds base information for the product, like
product_id, name etc.
>> Product.column_names
=> ["product_id", "name"]

the properties table holds extra "columns" for the products table, but
the column "name" in this table should actually be a method for
Products
>> Property.column_names
=> ["property_id", "name", "description",
"position"]

the third table product_properties holds the mapping data between
products and properties
>> ProductProperty.column_names
=> [ "product_property_id", "product_id",
"property_id", "value"]

If I do this:
>> Property.create(:name => ''color'')
I would like to be able to do:
>> Product.create(:name => "Glass", :color =>
"transparent")
and
>> Product.find(:all, :conditions =>
["color=?","transparent"])
or
>> Product.color
=> "transparent"

or
>> Product.color = "red"
where saving/retrieving the "color" method saves/retrieves the values
to/from ProductProperties.

Is this possible, and if not what is the best place to start coding?


--
Sincerely,

Frodo Larik

On May 5, 2006, at 10:26 AM, Frodo Larik wrote:
> Hi all,
>
> I wondered if the following is implemented in ActiveRecord:
>
> I have three tables: "products", "properties" and
"product_properties"
>
> the products table holds base information for the product, like
> product_id, name etc.
Active Record does not automatically map multivalued attributes in  
this way, though it could make a tasty plugin.

Do you need to do ad-hoc SQL queries on these attributes?  If not,  
consider serializing a hash of attributes to a single column rather  
than mapping them to a table.

> Is this possible, and if not what is the best place to start coding?
Yes; it is possible. Sketch out some unit tests demonstrating the  
behavior you''d like.

Try subclassing ActiveRecord::Base and overriding read_ and  
write_attribute to work with an has_many :attributes instead of  
@attributes.

Run the tests; repeat.


Best,
jeremy