# How do I validate a numeric field? **URL:** \ **Category:** Rails\ **Created:** [December 8, 2005, 10:23pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814 "2005-12-08T22:23:08Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:23pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/1 "2005-12-08T22:23:08Z")
Hello, I have a quanity field in my form that should have a length of no more than 3. I tried validate\_length\_of :qty, :maximum =\> 3 and this fails Thanks Frank ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:31pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/2 "2005-12-08T22:31:16Z")
Frank, try this: validate\_format\_of :qty, /[1-9][\d]{0,2}/ That should get you a non-zero digit, followed by up to two more digits. - Jamie ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:39pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/3 "2005-12-08T22:39:43Z")
I get Application error (Rails) Frank ----- Original Message ----- From: “Jamie M.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Sent: Thursday, December 08, 2005 4:27 PM Subject: Re: [Rails] how do I validate a numeric field? ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:39pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/4 "2005-12-08T22:39:45Z")
Frank wrote: > I have a quanity field in my form that should have a length of no more than 3. > > I tried validate\_length\_of :qty, :maximum =\> 3 > > and this fails Numbers don’t have a length. Just because a numeric value is 1001 doesn’t mean the variable has a “length” of 4. What you probably want to use is: validates\_inclusion\_of :qty, :in =\> 0…999 -Brian ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:43pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/5 "2005-12-08T22:43:48Z")
I’m guessing, but is “length” meant for strings and it should be something like validate\_with\_precision? something like that. bruce ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:43pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/6 "2005-12-08T22:43:49Z")
Jamie M. wrote: > try this: > > validate\_format\_of :qty, /[1-9][\d]{0,2}/ Just so we’re clear, the method is correctly named, “validates\_format\_of”, not “validate\_format\_of”. At least, that’s what my PDF copy of AWDwR says. But I wouldn’t use validates\_format\_of to check for a number within a certain range of values. That’s what validates\_inclusion\_of is for… -Brian ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:43pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/7 "2005-12-08T22:43:49Z")
Sorry, validates\_format\_of (with an S). I like Brian’s answer better though. ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 10:47pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/8 "2005-12-08T22:47:52Z")
Thanks, This worked: validates\_inclusion\_of :QTY1, :in =\> 0…999, :message =\> “must be between 0 and 999” Frank ----- Original Message ----- From: “Brian V. Hughes” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) To: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) Sent: Thursday, December 08, 2005 4:37 PM Subject: Re: [Rails] how do I validate a numeric field? ---
**Author:** ![farocco](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/f08c70/32.png) [@farocco](https://www.ruby-forum.com/u/farocco)\ **Post date:** [December 8, 2005, 11:53pm UTC](https://www.ruby-forum.com/t/how-do-i-validate-a-numeric-field/49814/9 "2005-12-08T23:53:02Z")
Hi Frank, You could use the \*validates\_numericality\_of(\*args) \*method. eg validates\_numericality\_of :qty, :only\_integer =\> true [http://api.rubyonrails.com/classes/ActiveRecord/Validations/ClassMethods.html#M000690](http://api.rubyonrails.com/classes/ActiveRecord/Validations/ClassMethods.html#M000690) Your model class can then include a validate method. This method is called before the model is saved, and you should protect it. ie protected def validate errors.add( :qty, “Should be between 0 and 1000”) unless ( :qty.nil? || (:qty \>= 0 and :qty \< 1000)) end This information came from the Agile web Development with Rails book modified for this situation. It is a great book when your starting with Rails. Cheers Dan