Rails: Validating min and max length of a string but allowing it to be blank

Question

I have a field that I would like to validate. I want the field to be able to be left blank, but if a user is entering data I want it to be in a certain format. Currently I am using the below validations in the model, but this doesn't allow the user to leave it blank:

validates_length_of :foo, :maximum => 5
validates_length_of :foo, :minimum => 5

How do I write this to accomplish my goal?

quainjn · Answer 1 · 2013-02-21T20:47:48.437

156

You can also use this format:

validates :foo, length: {minimum: 5, maximum: 5}, allow_blank: true

Or since your min and max are the same, the following will also work:

validates :foo, length: {is: 5}, allow_blank: true

edited Feb 21 '13 at 20:47

answered Feb 21 '13 at 20:34

quainjn

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score 151 · Accepted Answer · edited Oct 11 '18 at 00:48

151

I think it might need something like:

validates_length_of :foo, minimum: 5, maximum: 5, allow_blank: true

More examples: ActiveRecord::Validations::ClassMethods

edited Oct 11 '18 at 00:48

Kieran Andrews

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answered Dec 14 '10 at 17:19

DigitalRoss

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for a specific size you can use the lenght constraint :is – GuiGreg Jul 14 '14 at 13:47

Fellow Stranger · Answer 3 · 2017-05-05T18:29:00.113

17

Or even more concise (with the new hash syntax), from the validates documentation:

validates :foo, length: 5..5, allow_blank: true

The upper limit should probably represent somehting more meaningful like "in: 5..20", but just answering the question to the letter.

edited May 05 '17 at 18:29

answered Mar 09 '13 at 20:31

Fellow Stranger

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In don't think `in` will work with strings, seems to be numbers only – ecoologic Jun 09 '15 at 02:42
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This should work instead `validates :foo, length: 2..5, allow_blank: true` but ` length: { is: 5}` would do in the OP's case – PhilT Apr 05 '16 at 15:07

score 13 · Answer 4 · answered Dec 14 '10 at 17:19

13

From the validates_length_of documentation:

validates_length_of :phone, :in => 7..32, :allow_blank => true

:allow_blank - Attribute may be blank; skip validation.

answered Dec 14 '10 at 17:19

Gareth

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score 3 · Answer 5 · answered Dec 14 '10 at 17:21

every validates_* accepts :if or :unless options

validates_length_of :foo, :maximum => 5, :if => :validate_foo_condition

where validate_foo_condition is method that returns true or false

you can also pass a Proc object:

validates_length_of :foo, :maximum => 5, :unless => Proc.new {|object| object.foo.blank?}

score 2 · Answer 6 · answered Aug 03 '16 at 19:42

2

validates_length_of :reason, minimum: 3, maximum: 30

rspec for the same is

it { should validate_length_of(:reason).is_at_least(3).is_at_most(30) }

answered Aug 03 '16 at 19:42

shiva kumar

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score 2 · Answer 7 · answered Dec 07 '16 at 12:52

2

How about that: validates_length_of :foo, is: 3, allow_blank: true

answered Dec 07 '16 at 12:52

shem

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score -1 · Answer 8 · answered Sep 10 '18 at 14:18

-1

Add in your model:

validates :color, length: { is: 7 }

color is a string:

t.string :color, null: false, default: '#0093FF', limit: 7

answered Sep 10 '18 at 14:18

Marlon Henry Schweigert

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codevoice · Answer 9 · 2010-12-14T17:35:10.140

-4

In your model e.g.

def validate
  errors.add_to_base 'error message' unless self.foo.length == 5 or self.foo.blanc?
end

edited Dec 14 '10 at 17:35

answered Dec 14 '10 at 17:20

codevoice

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Rails: Validating min and max length of a string but allowing it to be blank

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