How to check if an attribute has a presence validation in Ruby on Rails

Question

Is there a way to know if an attribute has a validation? Something like following:

Model.attribute.has_presence_validation?

Interesting question (+1). What is the context for using this? — lurker, Aug 21 '14 at 16:29
Thanks, in my case, will be to place "include_blank" to a dynamically generated select — el_quick, Aug 21 '14 at 16:35

score 8 · Accepted Answer · answered Aug 21 '14 at 17:18

Well not sure about simplest solution but I achieved this functionality with quite complexity. Maybe someone come up with some simpler solution. Here is the code which worked perfectly for me.

I get all the validations on a model, chose presence validations(ActiveRecord::Validations::PresenceValidator) and then select all of their attributes and used include to check attribute(:your_attribute)presence in this array

Model.validators.collect{|validation| validation if validation.class==ActiveRecord::Validations::PresenceValidator}.compact.collect(&:attributes).flatten.include? :your_attribute

you can change compare statement

validation.class==ActiveRecord::Validations::PresenceValidator

to get all other types validation i.e uniqueness etc

score 2 · Answer 2 · answered Sep 13 '16 at 10:02

For me, the following code is working (it is basically checking if any validator for given field is an instance of the presence validator):

MyModel.validators_on(:my_attribute).any?{|validator| validator.kind_of?(ActiveModel::Validations::PresenceValidator)}

niborg · Answer 3 · 2017-02-18T00:28:39.550

Combining some of the points in the other answers, I would have thought the following approach was most straightforward (Rails 4.2.7):

class Model < ActiveRecord::Base
  validates ... # Whatever your validation are

  def self.presence_required_attrs
    validators.select do |v|
      v.is_a?(ActiveRecord::Validations::PresenceValidator)
    end.map(&:attributes).flatten
  end
end

It's then as easy as:

Model.presence_required_attrs.include?(:my_attribute)

Edit:

More comprehensive solution I think is just having a helper or controller method:

def validated_attrs_for(model, validation)
    if validation.is_a?(String) || validation.is_a?(Symbol)
      klass = 'ActiveRecord::Validations::' \
              "#{validation.to_s.camelize}Validator"
      validation = klass.constantize
    end
    model.validators
         .select { |v| v.is_a?(validation) }
         .map(&:attributes)
         .flatten
end

Used:

validated_attrs_for(Model, :presence).include?(:my_attribute)

Just double check that the various validators (:presence, :uniqueness, etc.) correctly correspond to the appropriate Validator class -- I'm pretty sure they do, but haven't looked recently.

How to check if an attribute has a presence validation in Ruby on Rails

3 Answers3