Tip #14 - Custom Error Messages in Validations

April 23rd, 2008

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:

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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:

Country Iso can’t be blank

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:

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

Do your test again, and now you get:

Country Iso Country can’t be blank

Nup.. that’d didn’t really fix it.

Fortunately, the fix is easy:

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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:

Country can’t be blank

Much better!

blogLater

Mikel

Posted by mikel Filed in Ruby on Rails, Ruby on Rails Tips

5 Responses to “Tip #14 - Custom Error Messages in Validations”

  1. Ben Says:
    May 8th, 2008 at 06:57 AM

    Hey Great Tip! Thanks for the post. Any idea how to make sure that the form field remains tagged properly with the appropriate error class so that the css rule for an error field will be applied properly? ~Ben

  2. Henrik N Says:
    May 12th, 2008 at 08:46 PM

    Ben: You could do http://henrik.nyh.se/2007/12/full-error-messages-without-prepended-attribute-name.

    I believe another way would be to add_to_base and then add a nil error to the attribute: user.errors.add(:country_iso, nil)

    nil errors should not be listed in text but still get you the CSS error highlighting.

  3. Henrik N Says:
    May 12th, 2008 at 10:49 PM

    Ben: You could also do http://henrik.nyh.se/2007/12/change-displayed-column-name-in-rails-validation-messages

  4. Mikel Says:
    May 12th, 2008 at 11:19 PM

    Henrik: Nice solution! Go read Henrik’s solution, it’s quite neat!

  5. Vince Says:
    May 13th, 2008 at 01:45 AM

    Is there a way to change the table name as well for the error message? For example, I have an STI model “class Group < Assembly” so when there is an error saving a Group, the error message says “2 errors prohibited this assembly from being saved” but I would like it to say “3 errors prohibited this group from being saved”.

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