Using :uniq in has_and_belongs_to_many (habtm)

June 11, 2006

So, I was trying to be smart about my controller today, which manipulates portfolios of stocks. I have habtm associations in my models like this:


class Stock < ActiveRecord::Base
        has_and_belongs_to_many :portfolios
end


class Portfolio < ActiveRecord::Base
        belongs_to :user
        has_and_belongs_to_many :stocks
end

So, I was running into the problem of checking to see if a stock was already in a portfolio. After digging around thru .find for habtm, .include? for arrays, and such, I found that I could just specify the portfolio model like this:


class Portfolio < ActiveRecord::Base
        belongs_to :user
        has_and_belongs_to_many :stocks, :uniq => true
end

It works! No more pain for unique entries!



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Comments

  1. Riley

    June 11, 2006 at 11:41 PM

    Doesn’t this only work on retrieved objects? ie you can still insert duplicate portfolios_stocks, they just won’t be retrieved. Do you know if there is a way to prevent duplicate inserts (without having to manually lookup if it already exists).


  2. miguelgodinho.com

    June 11, 2006 at 11:41 PM

    create a composite index in migration file, following the same example:

    add\_index :portfolios\_stocks, [:portfolio\_id, :stock\_id], :unique => true

    not very elegant, as one will have to deal with runtime exceptions, but probably the fastest and most reliable way.