首先，你的luhn方法实现逻辑看起来不正确！只是纠正了这段代码：您可以通过调用CreditCard.luhn（“61789372994”）进行交叉验证。http://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers

def self.luhn(cc_number)
    result = 0
    nums = cc_number.to_s.chars.map(&:to_i)

    nums.each_with_index do |item, index|
      if index.odd?
        item *= 2 
        result +=  item > 9 ? item.to_s.chars.map(&:to_i).inject(:+) : item
      else
        result +=item
      end
    end

   return "valid" if (result % 10) == 0
   return 'invalid'
  end

接下来要调用它，只需使用以下代码：

Creditcard.luhn("61789372994") #will return "valid"

接下来，在您的情况下，您可能正在尝试以下功能：- 你想验证卡号，如果它是有效的，然后保存记录-如果它是无效的，然后不存储卡，并有一个有效的错误消息。在这种情况下，你可以去以下方法：

#credit_card.rb
Class CreditCard < ActiveRecord::Base 
 #custom  validations.
 validate :valid_card_number? 
  validate :valid_card_type?

  private
  def valid_card_number?
    cc_number = self.number #see your controller#credit_card_params
    #above luhn method body goes here. 
     if (result % 10) == 0  #result you will get from the luhn method.
      errors.add(:number, 'Sorry, an invalid cardNumber Entered')
     end
  end

  def valid_card_type?
   #like valid_card_number? implement this one as well. 
  end
end

现在，在控制器中，当我们试图保存这些信用卡记录时，上述验证将自动执行。

#credit_cards_controller.rb
    def create
      @credit_card = CreditCard.new(credit_card_params)
      respond_to do |format|
        if @credit_card.save
          format.html { redirect_to @credit_card, notice: 'Credit card was successfully created.' }
          format.json { render :show, status: :created, location: @credit_card }
        else
          format.html { render :new }
          format.json { render json: @credit_card.errors, status: :unprocessable_entity }
        end
      end

因为我不确定你在哪里调用你的方法，或者你最终想做什么，我不确定这是正确的，但对我来说，这些方法不应该是类方法。

class CreditCard < ActiveRecord::Base
  before_validation :set_type
  validates :number, presence:true, length: { maximum: 16}
  validate :check_luhn

  #Methods for luhn validation

  #First checking the type of card
  def set_type
    # Making sure that the card number is passed as a string
    credit_card_number = number.to_s
    # Set of statements to return the appropriate card type
    # Firstly the code checks the cards's length
    # Secondly regexp, returns 0 which signals validation
    self.type = 'Amex' if credit_card.length == 15 && (credit_card =~ /^(34|37)/) == 0
    self.type = 'Discover' if credit_card.length == 16 && (credit_card =~ /^6011/) == 0
    self.type = 'MasterCard' if credit_card.length == 16 && (credit_card =~ /^(5[1-5])/) == 0
    self.type = 'VISA'   if [13,16].include?(credit_card.length) && (credit_card =~ /^4/) == 0
    self.type = 'Unknown'
  end

  #Secondly applying the Luhn algorithm on the number to check is the number valid or not

  def check_luhn
    result = 0
    nums = number.to_s.split("")
    nums.each_with_index do |item, index|
      if index.even?
        result += item.to_i * 2 >9 ? item.to_i*2-9 : item.to_i*2
      else
        result +=item.to_i
        end
    end
    if (result % 10) != 0
      errors.add(:number, 'is not a valid credit card number')
    end
  end    
end

因此，我在验证之前根据信用卡号设置了类型，并使luhn检查成为验证，在检查失败时添加了一个错误。
这意味着在你的控制器中你可以有一个标准的rails动作：

def create
  @credit_card = CreditCard.new(credit_card_params)

  respond_to do |format|
    if @credit_card.save
      format.html { redirect_to @credit_card, notice: 'Credit card was successfully created.' }
      format.json { render :show, status: :created, location: @credit_card }
    else
      format.html { render :new }
      format.json { render json: @credit_card.errors, status: :unprocessable_entity }
    end
  end
end

然后，如果新操作无效，它将呈现新操作，您只需向用户显示错误。
我将把代码其余部分的重构/更改留给您。