Validates whether the value of the specified attribute is of the correct form by matching it against the regular expression provided.

class Person < ActiveRecord::Base
  validates_format_of :email, :with => /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i, :on => :create
end

Note: use \A and \Z to match the start and end of the string, ^ and $ match the start/end of a line.

A regular expression must be provided or else an exception will be raised.

Configuration options:

• message - A custom error message (default is: "is invalid")
• with - The regular expression used to validate the format with (note: must be supplied!)
• 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 718
def validates_format_of(*attr_names)
  configuration = { :message => ActiveRecord::Errors.default_error_messages[:invalid], :on => :save, :with => nil }
  configuration.update(attr_names.extract_options!)

  raise(ArgumentError, "A regular expression must be supplied as the :with option of the configuration hash") unless configuration[:with].is_a?(Regexp)

  validates_each(attr_names, configuration) do |record, attr_name, value|
    record.errors.add(attr_name, configuration[:message]) unless value.to_s =~ configuration[:with]
  end
end