# Validation for one or another field **URL:** \ **Category:** rubyonrails-talk\ **Created:** [March 16, 2011, 7:51pm UTC](https://discuss.rubyonrails.org/t/validation-for-one-or-another-field/57941 "2011-03-16T19:51:07Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Rodrigo\_Alves\_Vieira](https://avatars.discourse-cdn.com/v4/letter/r/13edae/32.png) [@Rodrigo\_Alves\_Vieira](https://discuss.rubyonrails.org/u/Rodrigo_Alves_Vieira)\ **Post date:** [March 16, 2011, 7:51pm UTC](https://discuss.rubyonrails.org/t/validation-for-one-or-another-field/57941/1 "2011-03-16T19:51:07Z")
Hello everyone, in my model I have amongst other fields, the :variant\_id and :cart\_id, I want to validate their presences but in my app the user only needs to set one of them, so I can’t make it validates\_presence\_of :variant\_id, :cart\_id. I am sure there’s a solution for that, please tell me if you know! Thanks! ---
**Author:** ![Philip\_Hallstrom](https://avatars.discourse-cdn.com/v4/letter/p/bbe5ce/32.png) [@Philip\_Hallstrom](https://discuss.rubyonrails.org/u/Philip_Hallstrom)\ **Post date:** [March 16, 2011, 9:13pm UTC](https://discuss.rubyonrails.org/t/validation-for-one-or-another-field/57941/2 "2011-03-16T21:13:08Z")
> Hello everyone, in my model I have amongst other fields, the :variant\_id and :cart\_id, I want to validate their presences but in my app the user only needs to set one of them, so I can't make it validates\_presence\_of :variant\_id, :cart\_id. > > I am sure there's a solution for that, please tell me if you know! You can either write a custom validation method that returns false if both are unset or you could add some :if =\> {...} code to your validation line so it only validates one field if the other is blank. You'd need that on both validation lines and your error message would be a little confusing suggesting the user needs to pick both. If it was me, I'd go custom so I could put up a reasonable error message.