Rails - Dec 2006 - Dynamic # of Attributes for a Model (key/val table) Get/Set?

I''m working on a simple product catalog. Products have user defined
attributes, such as: color, size, weight. More attributes can be added
at any time. Since these attributes are not known ahead of time, they
cannot be created as columns.

My table structure (simplified):

products
--------
id
name

attrs
--------
id
name

product_attrs
--------
id
attr_id
value

And some sample code:

## Create some attributes
##    1 - size
##    2 - color
##    3 - weight
[''size'',''color'',''weight''].each
do |attr|
  Attr.create( { ''name'' => attr } )
end

## Create a new product
p = Product.new( { ''name'' => ''Widget'' } )

## Assign some attributes
p.product_attrs << ProductAttr.create( { ''attr_id'' =>
1 } )  # size
p.product_attrs << ProductAttr.create( { ''attr_id'' =>
2 } )  # color
p.product_attrs << ProductAttr.create( { ''attr_id'' =>
3 } )  # weight

## Output
p.product_attrs.collect{ |product_attr| product_attr.name } => [size,
color, weight]

## Product ''p'' now has 3 ProductAttributes associated with it
(which in
turn are associated with the three attributes [size, color, weight]
created above)

Now that the product has associated attributes -- I''d like an easy way
to get and set their values. Is there any way to do something like:

p.product_attrs[''color''] = ''red''
-or-
p.product_attrs.color = ''red''

Right now, the only way I''ve gotten this to work is with:

p.product_attrs.find( Attr.find_by_name(''color'') ).value =
''red''

...which isn''t all that nice looking. I could probably hack something
up, but I figure I''d ask first.

Maybe I''m even on the wrong path here and somebody else has a clue as
to
how I can organize this data all together. Is there an ideal way of
handling a dynamic number of Model attributes with (or without) using a
key/value type table structure as I describe above (The
''attributes''
table defines the key, the ''product_attributes'' defines the
value).

Best,
J

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On 12/5/06, J. Riddel
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> I''m working on a simple product catalog. Products have user
defined
> attributes, such as: color, size, weight. More attributes can be added
> at any time. Since these attributes are not known ahead of time, they
> cannot be created as columns.
>
## Assign some attributes
> p.product_attrs << ProductAttr.create( { ''attr_id''
=> 1 } )  # size
> p.product_attrs << ProductAttr.create( { ''attr_id''
=> 2 } )  # color
> p.product_attrs << ProductAttr.create( { ''attr_id''
=> 3 } )  # weight
>
> ...which isn''t all that nice looking. I could probably hack
something
> up, but I figure I''d ask first.

I would start with creating some collection class, that will allow using
indexers (or even through method_missing) to access product''s custom
attributes. Something like that:

my_product.attrs[:size]   or   my_product.attrs.size

It is easy: instantiate collection class and pass product id to it. Then
when you try to access some attributes, just do ProductAttr.find( yada yada
) to get attribute value.

After that you could think even further and implement custom attributes
interception in Product''s method_missing (to allow my_product.size).


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J. Riddel wrote:
> I''m working on a simple product catalog. Products have user
defined
> attributes, such as: color, size, weight. More attributes can be added
> at any time. Since these attributes are not known ahead of time, they
> cannot be created as columns.
Let me suggest I a plugin I have created for this purpose.

https://rubyforge.org/projects/flex-attributes/

The plugin is still in "beta" since the application it is made for has
not been rolled out to production but it seems to work well.

Basically your model looks something like:

class Product < ActiveRecord::Base
   has_flex_attributes
end

Then you can just add/remove attributes as you need. If the attribute 
exists on the model it will be stored there. If it does not then it will 
be stored in a "thin" table called product_attributes.

There are also hooks so you can define what attributes are valid. 
Finally the plugin works with 
acts_as_versioned/acts_as_versioned_association.

The docs are a little scattered right now because the product it was 
created for is still in development but you are welcome to use what I have.

Eric


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> 
> Let me suggest I a plugin I have created for this purpose.
> 
> https://rubyforge.org/projects/flex-attributes/
> 
I came up with a solution using MethodMissing, but your plugin looks to 
be what I need. However, there is nothing to download from that link? 
Can you add the files?


J

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J. Riddel wrote:
> 
>> 
>> Let me suggest I a plugin I have created for this purpose.
>> 
>> https://rubyforge.org/projects/flex-attributes/
>> 
> 
> I came up with a solution using MethodMissing, but your plugin looks to 
> be what I need. However, there is nothing to download from that link? 
> Can you add the files?
> 
> 
> J
Nevermind, it was in SVN. RubyForge just showed that it had 0 CVS and 
SVN commits.

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Eric --

Thanks a lot. This works great. Slightly different than what I came up 
with (in 10 lines with MethodMissing), but it "feels" better and 
actually makes my relationship less complicated. Thanks a lot. Great 
timing.

J


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J. Riddel wrote:
> Thanks a lot. This works great. Slightly different than what I came up 
> with (in 10 lines with MethodMissing), but it "feels" better and 
> actually makes my relationship less complicated. Thanks a lot. Great 
> timing.
Glad it is working for you. The plugin started out simple but I needed 
to also support acts_as_versioned (so the related attributes are 
versioned) which made the plugin much more complicated.

If you (or anybody that uses this plugin) get any problems send me a 
message. It is fairly new (the site it was developed for hasn''t even
hit
production yet) so there may be some issues with it still.

Eric


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Good idea, I''ll take a look at it as well.


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