rails validation: :allow_nil and :inclusion both needed at the same time

Question

Usually the field 'kind' should be allowed blank. but if it is not blank, the value should included in ['a', 'b']

validates_inclusion_of :kind, :in => ['a', 'b'], :allow_nil => true

The code does not work?

you tell us, did it work in your tests? – tokland Jun 28 '13 at 08:02 — tokland, Jun 28 '13 at 08:02
it does not work in my rspec? – Daniel Jun 28 '13 at 08:04 — Daniel, Jun 28 '13 at 08:04

score 52 · Answer 1 · answered Mar 06 '17 at 14:58

52

In Rails 5 you can use allow_blank: true outside or inside inclusion block:

validates :kind, inclusion: { in: ['a', 'b'], allow_blank: true }

or

validates :kind, inclusion: { in: ['a', 'b'] }, allow_blank: true

tip: you can use in: %w(a b) for text values

answered Mar 06 '17 at 14:58

vasylmeister

Rails 5.2: `allow_blank` and `allow_nil` both work independently. You'll need to restart the web server if you're changing this code in your model.rb. – MSC Dec 13 '18 at 05:34
3

Rails 5.2: `allow_nil` does _not_ work either inside or outside the hash. `allow_blank` _does_ work. – tfwright Mar 12 '19 at 16:08
2

Note, the difference in placement affects the error message(s) generated when the the attribute fails validation. – jbarr Jun 06 '19 at 17:49

score 50 · Answer 2 · answered Jun 28 '13 at 08:18

50

This syntax will perform inclusion validation while allowing nils:

validates :kind, :inclusion => { :in => ['a', 'b'] }, :allow_nil => true

answered Jun 28 '13 at 08:18

Matt

Not 100% sure but I think allow_nil might need to be inside of the inclusion hash – aceofspades Jun 28 '13 at 14:39
1

The syntax is correct for Rails 3.2 (tested), I don't know if your suggestion might be valid for another version? – Matt Jun 28 '13 at 15:57
Perhaps. It looks wrong to me because it is really an exception to the inclusion requirement, which by itself would fail. If it works it works! – aceofspades Jun 28 '13 at 18:19
2

It's an exception to any validation, if the value is blank, no further validation is performed. – rewritten Oct 17 '13 at 15:12

Oren · Answer 3 · 2014-03-11T12:55:29.513

9

check also :allow_blank => true

edited Mar 11 '14 at 12:55

answered Mar 11 '14 at 10:48

Oren

1

`allow_nil: true` did not work in a Rails 4 app I was working on. I can confirm that this does work in Rails 4. – Richard Jones Jul 17 '15 at 22:45
3

confirming `allow_nil: true` does NOT work in rails 5... this does work in Rails 5. – daino3 Dec 02 '16 at 16:23

score 3 · Answer 4 · answered Mar 21 '19 at 09:02

If you are trying to achieve this in Rails 5 in a belongs_to association, consider that the default behaviour requires the value to exist.

To opt out from this behaviour you must specify the optional flag:

belongs_to :foo, optional: true 

validates :foo, inclusion: { in: ['foo', 'bar'], allow_blank: true }

score 2 · Answer 5 · answered Aug 01 '19 at 17:09

In Rails 5.x you need, in addition to the following line, to call a before_validation method:

validates_inclusion_of :kind, :in => ['a', 'b'], :allow_nil => true

The before_validation is needed to convert the submitted blank value to nil, otherwise '' is not considered nil, like this:

  before_validation(on: [:create, :update]) do
    self.kind = nil if self.kind == ''
  end

For database disk space usage it is of course better to store nil's than storing empty values as empty strings.

5 Answers5