Allow users to create dynamic model attributes?

Question

In my Rails3 app, I am using ActiveRecord and Postgresql.

Say I have a model called Parts. The model has a small list of standard attributes such as price, quantity, etc.

However, Customer A might want to add LotNumber and CustomerB might want to add OriginalLocation.

How would I allow them to do that?

I thought about creating a PartsDetail model that allowed them to have a type.

class PartsDetail < ActiveRecord::Base
    attr_accessible :type, :value, :part_id
    belongs_to :parts
end

So that "type" could be "LotNumber", etc.

But I'm not quite sure how that would work in my associations and querying.

Any ideas?

Thanks.

Answer 1

Since you're using PostgreSQL, you could use hstore to store arbitrary hashes in database columns:

This module implements the hstore data type for storing sets of key/value pairs within a single PostgreSQL value. This can be useful in various scenarios, such as rows with many attributes that are rarely examined, or semi-structured data. Keys and values are simply text strings.

There's even a gem for adding hstore support to ActiveRecord:

https://github.com/softa/activerecord-postgres-hstore

Then you could create an hstore column called, say, client_specific and look inside it with things like:

M.where("client_specific -> 'likes' = 'pancakes'")
M.where("client_specific @> 'likes=>pancakes'")

to see which clients have noted that they like pancakes.

You might want to store a list of customer-specific fields somewhere with the customer record to make the UI side of things easier to deal with but that's pretty simple to do.