Adam Hooper's Engineering Tips

Full Sentences in Rails Validation Messages

This article assumes a rudimentary understanding of Rails Internationalization (or at least a working knowledge of Rails and a vague awareness that strings meant to be displayed to users can be stored outside of models, controllers, and views).

I will explain why Rails’s validation messages are incorrect, and I will provide a simple monkey-patch which can let you write less restricted validation messages. In the process, you should become more comfortable with translations and less comfortable with several Rails methods.


There is a golden rule in i18n (“internationalization”): do not use string concatenation.

Why String Concatenation Breaks…

An example: I once worked on a website which lists organizations in both English and Swahili. In English, one could write, “found 16 companies”; in Swahili, this might translate to, “masharika 16 yamekutanwa” (if I studied my grammar correctly).

A programmer might be tempted to write:

s = I18n.t('Found') + ' ' + number + ' ' + I18n.t('company', :count => number)

with a translations file containing

    one: company
    other: companies
  found: found

But in Swahili, the best this strategy could produce is, “Tumeyakutana 16 masharika,” which is completely out of order.

Instead, our intrepid programmer should write:

s = I18n.t('found n companies', :count => number)

with a translations file containing

  found n companies:
    zero: found no companies
    one: found one company
    other: 'found {{count}} companies'

In English, the output is identical. At first glance, one might find the translation file repetitive (and clearer to read). But the real gain is that our program can now be translated to any language (depending on the I18n backend). We can now write a Swahili version of the string (excuse my grammar if I get these wrong):

  found n companies:
    zero: masharika sifuri yamekutanwa
    one: sharika moja limekutanwa
    other: 'masharika {{count}} yamekutanwa'

Problem solved! And we learned a valuable moral: do not use string concatenation to build sentences.

… Even in a Single Language

Another example: suppose an ActiveRecord validation produces an error. Rails will normally return a string such as “title: can’t be blank”. You may want to adjust that message to, “Please enter a title.”

ActiveRecord does not support this use case, despite the fact that ActiveRecord validations are advertised as i18n-aware. Why? Because ActiveRecord, at least in Rails 2.3, has a nasty tendency to build sentences through string concatenation: an absolute no-no.

I can help you fix those validation messages.


ActiveRecord::Errors has a method called full_messages which returns a list of all error messages on an object. In Rails 2.3, full_messages is the unlikely arbiter of error messages. Let us examine the original:

    def full_messages(options = {})
      full_messages = [] 

      @errors.each_key do |attr|
        @errors[attr].each do |message|
          next unless message

          if attr == "base"
            full_messages << message
            attr_name = @base.class.human_attribute_name(attr)
            full_messages << attr_name + I18n.t('activerecord.errors.format.separator', :default => ' ') + message 

See the + signs next to I18n.t? Those are string concatenations: definitely off-limits. The funny thing is, by the time full_messages is called, all those messages have already been translated (in ActiveRecord::Errors#add).

Getting confused? That is not your fault. Suffice it to say, validations in Rails 2.3 are crufty, confusing, and ultimately incorrect.

The fix is simple: just remove the fancy logic from ActiveRecord::Errors#full_messages.

In your Rails project, put this in config/initializers/fix_active_record_validations_full_messages.rb:

# Ensures that when we pass a :message parameter to our validations, that
# message is a sentence (and not something to be prefixed by the column
# name). Rationale: ActiveSupport::Inflector is in over its head on this
# one.
# So instead of:
#   validates_presence_of :name, :message => 'should not be blank'
# Use:
#   validates_presence_of :name, :message => 'Name should not be blank'
# If, however, you just use:
#   validates_presence_of :name
# The behavior will remain unchanged.
if RAILS_GEM_VERSION =~ /^2\.3/
  ActiveRecord::Errors.class_eval do
    # Remove complicated logic
    def full_messages
      returning full_messages = [] do
        @errors.each_key do |attr|
          @errors[attr].each do |msg|
            full_messages << msg if msg 


The default Rails 2.3 error messages do not interpolate the attribute name: as we saw above, that is done in Rails 2.3’s flawed ActiveRecord::Errors#full_messages.

The sensible thing to do is correct the messages which, I think everyone should agree, are incorrect (because—you guessed it!—they are not full sentences).

Write this in config/locales/en.yml (or wherever your translations take place):

        # Default messages: complete sentences
        inclusion: "{{attribute}}: is not included in the list"
        exclusion: "{{attribute}}: is reserved"
        invalid: "{{attribute}}: is invalid"
        confirmation: "{{attribute}}: doesn't match confirmation"
        accepted: "{{attribute}}: must be accepted"
        empty: "{{attribute}}: can't be empty"
        blank: "{{attribute}}: can't be blank"
        too_long: "{{attribute}}: is too long (maximum is {{count}} characters)"
        too_short: "{{attribute}} is too short (minimum is {{count}} characters)"
        wrong_length: "{{attribute}}: is the wrong length (should be {{count}} characters)" 
        taken: "{{attribute}}: has already been taken"
        not_a_number: "{{attribute}}: is not a number"
        greater_than: "{{attribute}}: must be greater than {{count}}"
        greater_than_or_equal_to: "{{attribute}}: must be greater than or equal to {{count}}"
        equal_to: "{{attribute}}: must be equal to {{count}}"
        less_than: "{{attribute}}: must be less than {{count}}"
        less_than_or_equal_to: "{{attribute}}: must be less than or equal to {{count}}"     
        odd: "{{attribute}}: must be odd"
        even: "{{attribute}}: must be even"

These are the default Rails 2.3 validation messages with the attribute thrown in. With this en.yml and the above-mentioned monkey-patch to ActiveRecord::Errors#full_messages, Rails 2.3 will superficially behave identically to a non-monkey-patched version.

(Personally, I take this opportunity to make Rails’s default messages more human-friendly, by removing colons, adding periods, and rephrasing some sentences.)


With our groundwork in place, Rails gets out of the way and lets us write what we want.

For instance, suppose we have an Article with a :body and a :title, both validated using validates_presence_of, with an extra validates_length_of on the :title. We can add the following in config/locales/en.yml, within the en: { active_record: { errors: ... } } section (alongside messages):

              blank: Please enter body text for your article.
              blank: Your article is desperately seeking a title.
              too_long: "Your article's title cannot exceed {{count}} characters. Give it a trim."

And there you have it: full sentences in validation messages.

The Last Word

I started this article under the guise of internationalization, but my actual code and use case are purely English. This is because you should not build sentences using string concatenation, no matter which language you speak (or, for that matter, in which language you program).

This article should help you avoid string concatenation in one part of Rails 2.3; there are many other errors in Rails 2.3 and perhaps even in your own code, and I hope you feel better-equipped to remedy those problems as well.

Appendix: Other Confusing Rails Methods

Here is a list of Rails methods which you should think before using:

  • ActiveSupport::Inflector#titleize (Never use this: it does not translate, and even in English it will fail you every time. Even the string used as an example in the method’s documentation, “Man From The Boondocks,” is titleized incorrectly by this method.)
  • ActiveSupport::Inflector#humanize (Never use this unless you are rewriting Rails’s internals. Maybe you want ActiveRecord::Base#human_attribute_name and ActiveRecord::Base#human_name?)
  • ActiveSupport::Inflector#ordinalize (If you mean to translate your application to non-English and you use ordinalize, you will need to override this method or define a replacement.)
  • ActiveSupport::CoreExtensions::String::Inflector#singularize and ActiveSupport::Inflector#singularize (Never singularize user-input strings, but feel free to singularize hard-coded strings such as class names and method names.)
  • ActiveSupport::CoreExtensions::String::Inflector#pluralize and ActiveSupport::Inflector#pluralize (Never pluralize user-input strings, but feel free to pluralize hard-coded strings such as class names and method names.)
  • I18n::Backend::Simple#pluralize (The Simple I18n backend is only correct for English and a few other languages (by happenstance)—pluralization rules are different in different languages. If you later translate to a language with more complex pluralization rules than “zero/one/many”, you will need to replace the I18n backend for a more complete pluralize method, but you will not need to change the files which called pluralize.)
  • ActionView::Helpers::TextHelper#pluralize (This is the helper you can call from your views. Never use it: it does not translate to other languages, and even in English you should be writing special strings instead of displaying “0” and “1”, as a matter of style.)