ruby on rails has_one association with unique

Question

Hey I have a model foo that has_one :bar. And bar belongs_to :foo. I was wondering if there is a way to augment the has_one such that no two bars can belong to the same foo. I looked at the documentation for has_one and it seems like there is no :uniq parameter which I am allowed to specify. So do I have to create a custom validation to achieve this? Or is there an easier way?

Thanks.

Fornax

Answer 1

You do not need a custom validation, just enforce uniqueness of bar for any given foo

class Bar < ActiveRecord::Base
  belongs_to :foo
  validates_uniqueness_of :foo_id
end

Second

This would ensure that no two foos have the same bar, but @dhruvg is looking to ensure that no two bars belong to the same foo. – Horsefly

As mentioned by @pynix-wang, validation of uniqueness does not guaranty anything in concurrent environments. You should use unique index – Modestia

Answer 2

add a uniq index to foo_id in table bars so you can not create 2 bars with same foo_id, so only one bar can belongs to foo

Malena

validates_uniqueness_of may not uniq in a concurrency environment. – Malena

you might also need to create a unique index and/or a foreign key constraint on the supplier column for the accounts table.From Rails Guide – Malena

Answer 3

I think you should write your own validation, because two different record of Foo has no idea about others related record (Bar)

Tradition

Irrelevent. That would be of concern if he wanted no two Foo's to have the same Bar. But that's not what he asked. – Airspace