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Sometimes we may need to validate record only under certain conditions.

class User < ApplicationRecord
  validates :name, presence: true, if: :admin? 

  def admin?
    conditional here that returns boolean value
  end
end
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  • If we conditional is really small,
  • We can use a Proc:
class User < ApplicationRecord
  validates :first_name, presence: true, if: Proc.new { |user| user.last_name.blank? }
end
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Negative conditional we can use unless:

class User < ApplicationRecord
  validates :first_name, presence: true, unless: Proc.new { |user| user.last_name.present? }
end
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we can also pass a string, which will be executed via instance_eval:

class User < ApplicationRecord
  validates :first_name, presence: true, if: 'last_name.blank?'
end
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