validates_length_of(*attrs) public

Validates that the specified attribute matches the length restrictions supplied. Only one option can be used at a time:

  class Person < ActiveRecord::Base
    validates_length_of :first_name, :maximum=>30
    validates_length_of :last_name, :maximum=>30, :message=>"less than %d if you don't mind"
    validates_length_of :fax, :in => 7..32, :allow_nil => true
    validates_length_of :user_name, :within => 6..20, :too_long => "pick a shorter name", :too_short => "pick a longer name"
    validates_length_of :fav_bra_size, :minimum=>1, :too_short=>"please enter at least %d character"
    validates_length_of :smurf_leader, :is=>4, :message=>"papa is spelled with %d characters... don't play me."

Configuration options:

  • minimum - The minimum size of the attribute
  • maximum - The maximum size of the attribute
  • is - The exact size of the attribute
  • within - A range specifying the minimum and maximum size of the attribute
  • in - A synonym(or alias) for :within
  • allow_nil - Attribute may be nil; skip validation.
  • too_long - The error message if the attribute goes over the maximum (default is: "is too long (maximum is %d characters)")
  • too_short - The error message if the attribute goes under the minimum (default is: "is too short (min is %d characters)")
  • wrong_length - The error message if using the :is method and the attribute is the wrong size (default is: "is the wrong length (should be %d characters)")
  • message - The error message to use for a :minimum, :maximum, or :is violation. An alias of the appropriate too_long/too_short/wrong_length message
  • 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.

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March 13, 2010
3 thanks

Can be used with has_many associations

You can also use this to validate that a has_many association has a specified number of records on the other end:

has_many :members

validates_length_of :members, :minimum => 1