问题
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?
回答1:
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.)
来源：https://stackoverflow.com/questions/2533502/rails-3-validate-combined-values