Consider a User model with a validation for the name attribute like this:
class User < ApplicationRecord validates :name, presence: true end
The key for the error message in this case is
:blank. Active Record will look up this key in the namespaces:
This link contains a table of all the message names for use with
config/locales/en.yml (or any other locale). The names are somewhat arbitrary, so it’s handy to have this for reference.