Rails: Validating a Date Greater than Another

Question

I'm writing a custom validator in ActiveRecord so that a deadline makes sense:

  validate :deadline_is_possible?

  def deadline_is_possible?
    if deadline > begins_at
      errors.add(:deadline, 'must be possible')
    end
  end

This however generates a "NoMethodError: undefined method `>' for nil:NilClass". I event tried to turn the dates into strings, like:

  def deadline_is_possible?
    if deadline.to_s > begins_at.to_s
      errors.add(:deadline, 'must be possible')
    end
  end

and though it doesn't generate an error, doesn't work either.

I also declared other validators (such as

  def begins_at_is_date?
    if !begins_at.is_a?(Date)
      errors.add(:begins_at, 'must be a date')
    end
  end

that work OK.

Answer 1

You can use comparison:

   validates :deadline, comparison: { greater_than: :begins_at }

Doc: https://guides.rubyonrails.org/active_record_validations.html#comparison

Answer 2

You can add your own validator:

class AfterDateValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    return if value.blank?

    other_date = record.public_send(options.fetch(:with))

    return if other_date.blank?

    if value < other_date
      record.errors.add(attribute, (options[:message] || "must be after #{options[:with].to_s.humanize}"))
    end
  end
end

And use it in a model:

validates :invited_on, presence: true
validates :selected_on, presence: true, after_date: :invited_on