ActiveRecord Validations Cheatsheet

Class convenience methods

validates_acceptance_of

Encapsulates the pattern of wanting to validate the acceptance of a terms of service check box (or similar agreement).

    validates_acceptance_of :terms_of_service
    validates_acceptance_of :eula, :message => "must be abided"

If the database column does not exist, the terms_of_service attribute is entirely virtual. This check is performed only if terms_of_service is not nil and by default on save.

validates_associated

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

    has_many :pages
    belongs_to :library
    validates_associated :pages, :library

Warning! If, after the above definition, you then wrote...

    belongs_to :book
    validates_associated :book

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

validates_confirmation_of

Encapsulates the pattern of wanting to validate a password or email address field with a confirmation. Example...

Model

    class Person < ActiveRecord::Base
      validates_confirmation_of :user_name, :password
      validates_confirmation_of :email_address, :message => "should match confirmation"
    end

View

    <%= password_field "person", "password" %>
    <%= password_field "person", "password_confirmation" %>

The added password_confirmation attribute is virtual: it exists only as an in-memory attribute for validating the password. To achieve this, the validation adds accessors to the model for the confirmation attribute. This check is performed only if password_confirmation is not nil, and by default only on save. To require confirmation, make sure to add a presence check for the confirmation attribute...

    validates_presence_of :password_confirmation, :if => :password_changed

validates_each

Validates each attribute against a block.

    validates_each :first_name, :last_name do |record, attr, value|
      record.errors.add attr, 'starts with z.' if value[0] == ?z
    end

validates_exclusion_of

Validates that the value of the specified attribute is not in a particular enumerable object.

    validates_exclusion_of :username, :in => %w( admin superuser ), :message => "You don't belong here"
    validates_exclusion_of :age, :in => 30..60, :message => "This site is only for under 30 and over 60"
    validates_exclusion_of :format, :in => %w( mov avi ), :message => "extension %s is not allowed"

validates_format_of

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

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

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.

validates_inclusion_of

Validates whether the value of the specified attribute is available in a particular enumerable object.

    validates_inclusion_of :gender, :in => %w( m f ), :message => "woah! what are you then!??!!"
    validates_inclusion_of :age, :in => 0..99
    validates_inclusion_of :format, :in => %w( jpg gif png ), :message => "extension %s is not included in the list" 

validates_length_of

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

    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 :phone, :in => 7..32, :allow_blank => 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."
    validates_length_of :essay, :minimum => 100, :too_short => "Your essay must be at least %d words."), :tokenizer => lambda {|str| str.scan(/\w+/) }

validates_numericality_of

Validates whether the value of the specified attribute is numeric by trying to convert it to a float with Kernel.Float (if only_integer is false) or applying it to the regular expression /\A[+\-]?\d+\Z/ (if only_integer is set to true).

    validates_numericality_of :age, :greater_than => 18

validates_presence_of

Validates that the specified attributes are not blank (as defined by blank?). Happens by default on save.

    validates_presence_of :first_name 

The first_name attribute must be in the object and it cannot be blank.

If you want to validate the presence of a boolean field (where the real values are true and false), you will want to use validates_inclusion_of :field_name, :in => [true, false] This is due to the way blank? handles boolean values.

validates_size_of

Alias for validates_length_of

validates_uniqueness_of

Validates whether the value of the specified attributes are unique across the system. Useful for making sure that only one user can be named "davidhh".

    validates_uniqueness_of :user_name

It can also validate whether the value of the specified attributes are unique based on multiple scope parameters. For example, making sure that a teacher can only be on the schedule once per semester for a particular class.

    validates_uniqueness_of :teacher_id, :scope => [:semester_id, :class_id]

When the record is created, a check is performed to make sure that no record exists in the database with the given value for the specified attribute (that maps to a column). When the record is updated, the same check is made but disregarding the record itself.

Because this check is performed outside the database there is still a chance that duplicate values will be inserted in two parallel transactions. To guarantee against this you should create a unique index on the field. See add_index for more information.

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