How to validate presence of an array using Enumerize?

I'm trying to implement to validations on a given model array-like field, using the Enumerize Gem. I want to:

validate that all the elements of a list belong to a given subset, using Enumerize
validate that the list is not empty (using validates :field, presence: true)

It seems that when I provide a list containing an empty string, the presence validator fails. See this example.

class MyModel
  include ActiveModel::Model
  extend Enumerize

  enumerize :cities, in: %w(Boston London Berlin Paris), multiple: true
  validates :cities, presence: true
end


# Does not behave as expected
a = MyModel.new(cities: [""])
a.cities.present?  # => false
a.valid?  # => true, while it should be false.

It seems to work in some other cases (for instance when you provide a non empty string that is not in the Enum). For instance

# Behaves as expected
a = MyModel.new(cities: ["Dublin"])
a.cities.present?  # => false
a.valid?  # => false

Is there a workaround available to be able to use both Enumerize validation and ActiveModel presence validation?

Thanks!

Solution

The enumerize gem is saving your multiple values as an string array. Something like this: "[\"Boston\"]". So, with an empty array you have: "[]". The presencevalidator uses blank? method to check if the value is present or not. "[]".blank? returns false obviously.

So, you can try some alternatives:

Option 1:

validates :cities, inclusion: { in: %w(Boston London Berlin Paris) }

Option 2:

Add a custom validator

validate :ensure_valid_cities

def ensure_valid_cities
  errors.add(:cities, "invalid") unless cities.values.empty?
end