Custom validation in Rails

If you have your own validates

class Invite
  validates :invitee_email, format: {
    with: /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i,
    message: "is not an email"
  }
end

class Invite
  validates :invitee_email, format: {
    with: Devise.email_regexp,
    allow_blank: false
  }
end

You can refactor it 

# app/validators/email_validator.rb
class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless value =~ /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
      record.errors[attribute] << (options[:message] || "is not an email")
    end
  end
end

class Invite
  # Rails "magic" infers the name of the validation
  validates :invitee_email, email: true
end

class EmailValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    unless value =~ Devise.email_regexp
      record.errors[attribute] << (options[:message] || "is not an email")
    end
  end
end