Rails validation error messages: Displaying only one error message per field

Question

Rails displays all validation error messages associated with a given field. If I have three validates_XXXXX_of :email, and I leave the field blank, I get three

Answer 1

I would display all the error messages on one line and in a sentence format. You don't want the user to fix one error and end up having another error he was not aware of after submission. Telling them all the rules will save them clicks. With that said, this is how I'd do it:

flash_message_now("error", 
   @album.errors.keys.map { |k| "#{Album.human_attribute_name(k)} #{@album.errors[k].to_sentence}"}.to_sentence
)

with flash_message_now defined in ApplicationController (you can add it to a helper)

def flash_message_now(type, text)
    flash.now[type] ||= []
    flash.now[type] << text
  end

Answer 2

[Update] Jan/2013 to Rails 3.2.x - update syntax; add spec

Inspired by new validation methods in Rails 3.0 I'm adding this tiny Validator. I call it ReduceValidator.

lib/reduce_validator.rb:

# show only one error message per field
#
class ReduceValidator < ActiveModel::EachValidator

  def validate_each(record, attribute, value)
    return until record.errors.messages.has_key?(attribute)
    record.errors[attribute].slice!(-1) until record.errors[attribute].size <= 1
  end
end

My Model looking like - notice the :reduce => true:

validates :title, :presence => true, :inclusion => { :in => %w[ Mr Mrs ] }, :reduce => true
validates :firstname, :presence => true, :length => { :within => 2..50 }, :format => { :without => /^\D{1}[.]/i }, :reduce => true
validates :lastname, :presence => true, :length => { :within => 2..50 }, :format => { :without => /^\D{1}[.]/i }, :reduce => true

Works like a charm in my current Rails Project. The advantageous is, i've put the validator only on a few fields not all.

spec/lib/reduce_validator_spec.rb:

require 'spec_helper'

describe ReduceValidator do

  let(:reduce_validator) { ReduceValidator.new({ :attributes => {} }) }

  let(:item) { mock_model("Item") }
  subject { item }

  before(:each) do
    item.errors.add(:name, "message one")
    item.errors.add(:name, "message two")
  end

  it { should have(2).error_on(:name) }

  it "should reduce error messages" do
    reduce_validator.validate_each(item, :name, '')
    should have(1).error_on(:name)
  end

end

Answer 3

How about this @event.errors[:title].first?

Answer 4

Similar to olovwia's answer:

<% @errors.keys.each do |attr| %>
 <%= "#{attr.capitalize} #{@errors[attr].first}."%>
<% end %>"

Answer 5

My monkey patch of ActiveModel::Errors class lib/core_ext/rails/active_model/errors.rb (I use this code for Ruby on Rails 5.0 release):

module ActiveModel
  class Errors

    # don't add an attribute's error message to details
    # if it already contains at least one message

    alias_method :old_add, :add

    def add(attribute, message = :invalid, options = {})
      if details[attribute.to_sym].size.zero?
        old_add(attribute, message, options)
      end
    end

  end
end

Create a file config/initializers/core_ext.rb and add a require core_ext/rails/active_model/errors.rb to it.

Answer 6

I use this code for Ruby on Rails 3.0 release, which I put in lib/core_ext/rails/active_model/errors.rb:

module ActiveModel
  class Errors
    def full_message_per_field
      messages_per_field = []
      handled_attributes = []

      each do |attribute, messages|
        next if handled_attributes.include? attribute
        messages = Array.wrap(messages)
        next if messages.empty?

        if attribute == :base
          messages_per_field << messages.first
        else
          attr_name = attribute.to_s.gsub('.', '_').humanize
          attr_name = @base.class.human_attribute_name(attribute, :default => attr_name)
          options = { :default => "%{attribute} %{message}", :attribute => attr_name }

          messages_per_field << I18n.t(:"errors.format", options.merge(:message => messages.first))
        end

        handled_attributes << attribute
      end

      messages_per_field
    end
  end
end

This is essentially the same code as ActiveModel::Errors#full_messages, but won't show more than one error per attribute. Be sure to require the file (say, in an initializer) and now you can call @model.errors.full_message_per_field do |message| ...