Tip #14 - Custom Error Messages in Validations

If you use Rails, you sometimes get a situation where the custom error messages just don’t work, here is how you can fix it…

Say you have a model with a field called ‘country_iso’ which specifies the ISO value of the country the person belongs to.

Database design concerns aside (you should really have it as country_id and a separate country_iso field) you might be stuck with this situation from a legacy database (like I was).

As this is a required field, you set the following in your model:

class User < ActiveRecord::Base
  validates_presence_of :country_iso
end

So, you go ahead and make a form which presents the country as just a select box, because you don’t want your users to worry about if Thailand is TH or TL, but then you don’t specify a country and the error message comes back to the user in nice big letters:

<span style="color:red">{=html}Country Iso can’t be blank</span>

Ugh!

Aside from the fact that Iso is capitalized badly, how many of YOUR users know that it stands for “International Standards Organization” and that a Country ISO is usually a two letter representation of the country? I’d wager about 3 of them have some idea :)

So you go in and change the validates line to:

class User < ActiveRecord::Base
  validates_presence_of :country_iso, :message => "Country can't be blank"
end

Do your test again, and now you get:

<span style="color:red">{=html}Country Iso Country can’t be blank</span> Nup.. that’d didn’t really fix it.

Fortunately, the fix is easy:

class User < ActiveRecord::Base
  validate do |user|
    user.errors.add_to_base("Country can't be blank") if user.country_iso.blank?
  end
end

Now, reload your view and you’ll get:

<span style="color:red">{=html}Country can’t be blank</span> Much better!

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