Rails 3: Validate combined values

Question

In Rails 2.x you can use validations to make sure you have a unique combined value like this:

validates_uniqueness_of :husband, :scope => :wife

In the corresponding migration it could look like this:

add_index :family, [:husband, :wife], :unique => true

This would make sure the husband/wife combination is unique in the database. Now, in Rails 3 the validation syntax changed and the scope attribute seems to be gone. It now looks like:

validates :husband, :presence => true

Any idea how I can achieve the combined validation in Rails 3? The Rails 2.x validations still work in Rails 3 so I can still use the first example but it looks so "old", are there better ways?

Solution

Bear with me. The way the validates method in ActiveModel works is to look for a Validator.

:presence => true looks for PresenceValidator and passes the options: true to the validator's initializer.

I think you want

validates :husband, :presence => true, :uniqueness => {:scope => :wife}

(The uniqueness validator is actually part of ActiveRecord, not ActiveModel. It's really interesting how the developers set this up. It's quite elegant.)

Comments

[Cimm]

This sounds awesome and clean and all but... it doesn't work in my sample 'one model project' I tried. Did you guys did anything special? I used 2 strings and also tried with 2 integers but the validations just pass.

[epochwolf]

I'm using validates :contents, :presence => true, :uniqueness => {:scope => :comment_thread_id, :message => "has been said already, please add something meaningful"}

[Cimm]

Oops, so sorry, my bad. I was trying the wrong test, it does work. Thank you for the super fast and excellent answer!

[Dave Hollingworth]

I know this is an old(ish) question, but I was just trying this same method and couldn't get it to work like this, I had to do two separate validation statements: validates :husband, :presence => true and validates :husband_id, :uniqueness => {:scope => :wife_id}

[epochwolf]

@fishwebby I'm using this validates :visibility, :presence => true, :inclusion => { :in => VISIBILITIES } with rails 3.0.3 and I haven't encountered that problem.

[Dave Hollingworth]

@epochwolf It's the :uniqueness bit that I couldn't get to work - I'm also on Rails 3.0.3 - as I got it to work with two separate validation statements I didn't investigate it any further.