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:

• message - A custom error message (default is: "is invalid")
• 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.
• unless - Specifies a method, proc or string to call to determine if the validation should not occur (e.g. :unless => :skip_validation, or :unless => Proc.new { |user| user.signup_step <= 2 }). The method, proc or string should return or evaluate to a true or false value.

Source Code

# File active_record/validations.rb, line 824
def validates_associated(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save }
  configuration.update(attr_names.extract_options!)

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless
      (value.is_a?(Array) ? value : [value]).inject(true) { |v, r| (r.nil? || r.valid?) && v }
  end
end