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Active Record Validation Errors Cheatsheet

Each ActiveRecord backed model in Rails has an errors object which errors are added to if the model fails validation. This cheatsheet covers methods available, default errors messages and view error helpers. More

Table of Contents

1. Class convenience methods

1.1. 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.

Options

Key	Value
:accept	Specifies value that is considered accepted. The default value is a string "1", which makes it easy to relate to an HTML checkbox. This should be set to true if you are validating a database column, since the attribute is typecast from "1" to true before validation.

1.2. 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

1.3. validates_confirmation_of

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

1.3.1. Model

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

1.3.2. 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

1.4. 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

1.5. 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"

Options

Key	Value
:in	An enumerable object of items that the value shouldn’t be part of

1.6. 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([^@ ]+)@((?:[-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.

Options

Key	Value
:with	The regular expression used to validate the format with

1.7. 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" 

Options

Key	Value
:in	An enumerable object of items that the value shouldn’t be part of

1.8. 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+/) }

Options

Key	Value
: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	Alias for :within
: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)")
:tokenizer	Specifies how to split up the attribute string 1

1.9. 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

Options

Key	Value
:only_integer	Specifies whether the value has to be an integer, e.g. an integral value (default is false)
:greater_than	Specifies the value must be greater than the supplied value
:greater_than_or_equal_to	Specifies the value must be greater than or equal the supplied value
:equal_to	Specifies the value must be equal to the supplied value
:less_than	Specifies the value must be less than the supplied value
:less_than_or_equal_to	Specifies the value must be less than or equal the supplied value
:odd	Specifies the value must be an odd number
:even	Specifies the value must be an even number

1.10. 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.

1.11. validates_size_of

Alias for validates_length_of

1.12. 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”.

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.

Options

Key	Value
:scope	One or more columns by which to limit the scope of the uniqueness constraint
:case_sensitive	Looks for an exact match. Ignored by non-text columns (false by default)

2. Common options

The above class convenience validation methods all take a hash of common options.

Key	Value
:message	a custom error message
:on	specifies when this validation is active (default is :save, other options :create, :update)
:allow_nil	skip validation if attribute is nil (default is false). Notice that for fixnum and float columns empty strings are converted to nil
:allow_blank	if set to true, skips this validation if the attribute is blank (default is false)
:if	specifies a method, proc or "string" to call to determine if the validation should occur 2
:unless	as :if, but used to determine if the validation should not occur

3. Low level validations

You can create your own validations by implementing the validate method (or the variations, validate_on_create and validate_on_update) in your model. The validate method will be called by ActiveRecord before every save or update, whilst the validate_on_create and validate_on_update methods will only be called when saving new records or updating existing records respectively. Most validation methods simply do two things:

• Inspect the attributes of an object and check whether their values pass one or more conditions (such as making sure a name attribute is not empty and/or that it matches a certain regular expression)
• If an attribute’s value does not pass, add an error message to it

3.1. Errors

Each ActiveRecord object has its own errors object which stores a list of errors related to that object and is accessible via the errors method on the object.

The errors object itself has a number of methods which enable you to both add to the list of errors, or inspect the object for errors which have already been added. For example, to add an error to the name attribute of an object, we would use the add method…

object.errors.add(:name, "shouldn't be empty!")

…and to retrieve errors on the :name attribute we could read from the errors object…

object.errors.on(:name)    # => "shouldn't be empty!"

You will find our cheatsheet ActiveRecord Validation Errors a useful resource for manipulating the errors object.

Here are some examples of implementing low-level, roll-your-own validation methods…

3.2. Example

class Person < ActiveRecord::Base
  protected
    def validate
      errors.add_on_empty %w( first_name last_name )
      errors.add("phone_number", "has invalid format") unless phone_number =~ /[0-9]*/
    end

    def validate_on_create # is only run the first time a new object is saved
      unless valid_discount?(membership_discount)
        errors.add("membership_discount", "has expired")
      end
    end

    def validate_on_update
      errors.add_to_base("No changes have occurred") if unchanged_attributes?
    end
end

person = Person.new("first_name" => "David", "phone_number" => "what?")
person.save                         # => false (and doesn't do the save)
person.errors.empty?                # => false
person.errors.count                 # => 2
person.errors.on "last_name"        # => "can't be empty"
person.errors.on "phone_number"     # => "has invalid format"
person.errors.each_full { |msg| puts msg }
                                # => "Last name can't be empty"
                                # => "Phone number has invalid format"

person.attributes = { "last_name" => "Heinemeier", "phone_number" => "555-555" }
person.save # => true (and person is now saved in the database)