validates_format_of

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# File activemodel/lib/active_model/validations/format.rb, line 27
 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

Using validates_format_of to validate URIs

You can use the validates_format_of with the regular expression in the URI library ensure valid URIs.

Example

require 'uri'
class Feed < ActiveRecord ::Base
 validates_format_of  :uri, :with => URI .regexp
end

RE: Using validates_format_of to validate URIs

Further to Olly’s note below, you can also specify the protocol to further limit the valid uri’s, else things like ‘ftp ://someurl.com’ (there’s only a space in there to get it to display on here) would be valid.

validates_format_of  :uri, :with => URI .regexp(['http'])

Take care when writing regex

When you want to validate a field for a continuous string you’d probably write something like this (if it’s really early in the morning and you didn’t have your coffee yet):

validates_format_of  :something => /\w/

At the first sight it looks like it’s working because something = "blahblahblah" is valid. However, so is this: something = "blah meh 55". It’s just that your regex matched a substring of the value and not the whole thing. The proper regex you’re looking for is actually:

validates_format_of  :something => /^\w$/

Re: Taking care when writing regex

Oleg’s example from above contains an error and a pitfall:

validates_format_of  :something => /^\w$/

The string "blahblahblah" doesn’t pass this validation. What Oleg ment is rather a continuous string of at least one alphanumeric character:

validates_format_of  :something => /^\w+$/

However, that’s no good neither because it contains a well hidden trap in case you are validating content from a textarea.

Ruby (both 1.8 and 1.9) always matches ^ and $ against the beginning and ending of lines and not the entire string. Thus "First linenSecond line" will pass the above validation although it’s clearly not a continuous string.

You should use A (replacement for ^) and z (replacement for $) instead as their scope is the entire string:

validates_format_of  :something => /\A\w+\z/

(A side note for those with a Perl background: Please note that the "s" modifier has a different meaning in Ruby and won’t do the trick here.)

No numbers or symbols

"Kyle", "Дети", "Niños", "Quan-lu", "た ち"

validates_format_of  :first_name, :with => /^([^\d\W]|[-])*$/

note: the example format regex is too lenient

The example regex for RFC 2822 email is too lenient. Sure it’s just an example, but it wound up in our code and we just had to fix it to match the RFC.

The regex as given allows any non-@ non-whitespace characters. But the RFC only allows these characters in mailbox names

alpha digit - ! \ # $ % & ' * + \ / = ? ^ _ ` { | } ~ ] +

and . is only allowed between atoms of 1 or more of the above.

Here’s the corrected regex:

:with => /\A([-a-z0-9!\#$%&'*+\/=?^_`{|}~]+\.)*[-a-z0-9!\#$%&'*+\/=?^_`{|}~]+@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z/i

Example Regex format matching

for phone and email

validates_format_of  :phone, with: /\A(\d{10}|\(?\d{3}\)?[-. ]\d{3}[-.]\d{4})\z/
validates_format_of  :email, with: /\A[\w]([^@\s,;]+)@(([\w-]+\.)+(com|edu|org|net|gov|mil|biz|info))\z/i