Validate presence of one field or another (XOR)

Question

How do I validate the presence of one field or another but not both and at least one ?

Answer 1

Example for rails 3.

class Transaction < ActiveRecord::Base
  validates_presence_of :date
  validates_presence_of :name

  validates_numericality_of :charge, :unless => proc{|obj| obj.charge.blank?}
  validates_numericality_of :payment, :unless => proc{|obj| obj.payment.blank?}


  validate :charge_xor_payment

  private

    def charge_xor_payment
      if !(charge.blank? ^ payment.blank?)
        errors[:base] << "Specify a charge or a payment, not both"
      end
    end
end

Answer 2

 validate :father_or_mother

#Father last name or Mother last name is compulsory

 def father_or_mother
        if father_last_name == "Last Name" or father_last_name.blank?
           errors.add(:father_last_name, "cant blank")
           errors.add(:mother_last_name, "cant blank")
        end
 end

Try above simple example.

Answer 3

Your code will work if you add conditionals to the numericality validations like so:

class Transaction < ActiveRecord::Base
    validates_presence_of :date
    validates_presence_of :name

    validates_numericality_of :charge, allow_nil: true
    validates_numericality_of :payment, allow_nil: true


    validate :charge_xor_payment

  private

    def charge_xor_payment
      unless charge.blank? ^ payment.blank?
        errors.add(:base, "Specify a charge or a payment, not both")
      end
    end

end

Answer 4

I put my answer to this question below. In this example :description and :keywords are fields which one of this not be blank:

  validate :some_was_present

  belongs_to :seo_customable, polymorphic: true

  def some_was_present
    desc = description.blank?
    errors.add(desc ? :description : :keywords, t('errors.messages.blank')) if desc && keywords.blank?
  end

Answer 5

class Transaction < ActiveRecord::Base
    validates_presence_of :date
    validates_presence_of :name

    validates_numericality_of :charge, allow_nil: true
    validates_numericality_of :payment, allow_nil: true


    validate :charge_xor_payment

  private

    def charge_xor_payment
      if [charge, payment].compact.count != 1
        errors.add(:base, "Specify a charge or a payment, not both")
      end
    end

end

You can even do this with 3 or more values:

if [month_day, week_day, hour].compact.count != 1

Answer 6

I think this is more idiomatic in Rails 3+:

e.g: For validating that one of user_name or email is present:

validates :user_name, presence: true, unless: ->(user){user.email.present?}
validates :email, presence: true, unless: ->(user){user.user_name.present?}