Shopify Ruby脚本错误排查：折扣码要求未满足（空购物车）

我开发了一款Shopify Ruby脚本，用于阻止促销码应用到带sale标签的商品上，功能符合预期，但总是出现第一行错误提示「discount code requirements not met (empty cart)」，求解决办法。

脚本代码如下：

# ================================ Customizable Settings ================================
# ================================================================
# Define the tag for products where discounts are not allowed.
# ================================================================
SALE_TAGS = ['sale', 'Sale'] # Tags used to identify sale products
REJECTION_MESSAGE = "Discount codes can't be used with Sale products"

# ================================ Script Code (do not edit) ================================
# ================================================================
# ProductSelector
# Finds matching products by the entered criteria.
# ================================================================
class ProductSelector
  def initialize(tags)
    @tags = tags.map(&:downcase)
  end

  def match?(line_item)
    product_tags = line_item.variant.product.tags.map(&:downcase)
    (@tags & product_tags).any?
  end
end

# ================================================================
# DisableDiscountCodesForProductsCampaign
# If any matching items are in the cart, the discount code is rejected.
# ================================================================
class DisableDiscountCodesForProductsCampaign
  def initialize(tags, message)
    @product_selector = ProductSelector.new(tags)
    @rejection_message = message
  end

  def run(cart)
    return if cart.discount_code.nil?

    if cart.line_items.any? { |line_item| @product_selector.match?(line_item) }
      cart.discount_code.reject(message: @rejection_message)
    end
  end
end

# ================================================================
# Campaign Execution
# ================================================================
campaign = DisableDiscountCodesForProductsCampaign.new(SALE_TAGS, REJECTION_MESSAGE)
campaign.run(Input.cart)
Output.cart = Input.cart

错误提示截图：

问题原因 #

这个错误是因为脚本在购物车为空时仍会触发折扣码校验逻辑，Shopify系统默认会抛出「empty cart」的错误提示，而你的脚本没有处理购物车为空的场景。

修复方案 #

修改DisableDiscountCodesForProductsCampaign类中的run方法，在开头新增购物车为空的判断，直接返回即可：

def run(cart)
  # 新增：购物车为空时直接返回，避免触发系统默认错误
  return if cart.line_items.empty?
  return if cart.discount_code.nil?

  if cart.line_items.any? { |line_item| @product_selector.match?(line_item) }
    cart.discount_code.reject(message: @rejection_message)
  end
end

额外优化建议 #

• 你的SALE_TAGS里同时写了sale和Sale，但代码中已经通过map(&:downcase)统一转为小写，所以可以简化成SALE_TAGS = ['sale']，减少冗余。
• 测试时覆盖三类场景：空购物车使用折扣码、购物车仅含促销商品使用折扣码、购物车无促销商品使用折扣码，确保所有场景逻辑正常。

内容的提问来源于stack exchange，提问作者WadeB