验证一个或另一个字段(XOR)的存在

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
return if charge.blank? ^ payment.blank?


errors.add(:base, 'Specify a charge or a payment, not both')
end
end

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

 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.

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

I think this is more idiomatic in Rails:

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? }

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

Validation using a Proc or Symbol with :if and :unless will get called right before validation happens.

So presence one of both fields may be like this:

validates :charge,
presence: true,
if: ->(user){user.charge.present? || user.payment.present?}
validates :payment,
presence: true,
if: ->(user){user.payment.present? || user.charge.present?}

The (example snippet) code has :if or :unless as latest item, however as declared in doc it will get called right before validation happens - so another checking will works after, if condition match.