How do I display Ruby on Rails form validation error messages one at a time?

Question

I'm trying to understand how I can achieve this. Can anyone advise me or point me in the right direction?

What I currently do, which is shown in the code snippet below, allows me to display 1 error from each field at a time. It’s not not quite exactly what I want to do.

I want to display 1 error message at a time. For example, “first name can't be blank”, then once that error has been resolved, the next error in the array of errors should be displayed. This should keep happening until all errors have been resolved.

<% @user.errors.each do |attr, msg| %>
<%= "#{attr} #{msg}" if @user.errors[attr].first == msg %> 
<% end %>

Answer 1

ActiveRecord stores validation errors in an array called errors. If you have a User model then you would access the validation errors in a given instance like so:

@user = User.create[params[:user]] # create will automatically call validators

if @user.errors.any? # If there are errors, do something

  # You can iterate through all messages by attribute type and validation message
  # This will be something like:
  # attribute = 'name'
  # message = 'cannot be left blank'
  @user.errors.each do |attribute, message|
    # do stuff for each error
  end

  # Or if you prefer, you can get the full message in single string, like so:
  # message = 'Name cannot be left blank'
  @users.errors.full_messages.each do |message|
    # do stuff for each error
  end

  # To get all errors associated with a single attribute, do the following:
  if @user.errors.include?(:name)
    name_errors = @user.errors[:name]

    if name_errors.kind_of?(Array)
      name_errors.each do |error|
        # do stuff for each error on the name attribute
      end
    else
      error = name_errors
      # do stuff for the one error on the name attribute.
    end
  end
end

Of course you can also do any of this in the views instead of the controller, should you want to just display the first error to the user or something.