/ Ruby on Rails
/
method

validates_associated

validates_associated(*attr_names)
public

Validates whether the associated object or objects are all valid themselves. Works with any kind of association. 

  class Book < ActiveRecord::Base
    has_many :pages
    belongs_to :library

    validates_associated :pages, :library
  end

Warning: If, after the above definition, you then wrote: 

  class Page < ActiveRecord::Base
    belongs_to :book

    validates_associated :book
  end

…this would specify a circular dependency and cause infinite recursion.

NOTE: This validation will not fail if the association hasn’t been assigned. If you want to ensure that the association is both present and guaranteed to be valid, you also need to use validates_presence_of.

Configuration options:

  • on Specifies when this validation is active (default is :save, other options :create, :update)
  • if - Specifies a method, proc or string to call to determine if the validation should

occur (e.g. :if => :allow_validation, or :if => Proc.new { |user| user.signup_step > 2 }). The method, proc or string should return or evaluate to a true or false value.

1Note

Use this for has_one associations instead

magnemg ยท Jul 11, 20141 thank

I have confirmed that validates_associated doesn't work with has_one associations, like @amasses said.

This however worked for me, so I recommend to use validates on the has_one association directly, like this:

class Book < ActiveRecord::Base
has_one :cover, validates: true
end