Vercel Commerce 购物车折扣功能实现指南

2025-05-19 20:43:29作者：尤峻淳Whitney

前言

在电商平台开发中，购物车折扣功能是提升用户体验和促进销售的重要手段。本文将详细介绍如何在基于Next.js的Vercel Commerce项目中实现完整的购物车折扣功能，包括折扣码的添加、移除和状态管理。

核心功能实现

1. GraphQL 突变定义

首先需要定义用于更新购物车折扣码的GraphQL突变操作：

mutation cartDiscountCodesUpdate ($cartId: ID!, $discountCodes: [String!]) {
  cartDiscountCodesUpdate(cartId: $cartId, discountCodes: $discountCodes) {
    cart {
      ...cart
    }
  }
}

这个突变操作接收购物车ID和折扣码数组作为参数，返回更新后的购物车信息。

2. Shopify API 交互函数

在项目lib目录下创建与Shopify API交互的函数：

export async function updateDiscounts(cartId: string, discounts: string[]): Promise<Cart> {
  const res = await shopifyFetch<ShopifyDiscountCartOperation>({
    query: CART_DISCOUNT_CODE_UPDATE_MUTATION,
    variables: {
      cartId,
      discountCodes: discounts
    },
    cache: 'no-store'
  });
  return reshapeCart(res.body.data.cartDiscountCodesUpdate.cart);
}

此函数封装了API调用，确保数据格式正确并处理缓存策略。

业务逻辑实现

1. 应用折扣码

export async function applyDiscount(prevState: any, formData: FormData) {
  const cartId = cookies().get('cartId')?.value;
  if (!cartId) return 'Missing cart ID';
  
  const schema = z.object({
    discountCode: z.string().min(1),
  });
  
  const parse = schema.safeParse({
    discountCode: formData.get("discountCode"),
  });

  if (!parse.success) return "Error applying discount. Discount code required.";

  const data = parse.data;
  let discountCodes = [];
  discountCodes.push(data.discountCode);
  
  try {
    await updateDiscounts(cartId, discountCodes);
    revalidateTag(TAGS.cart);
  } catch (e) {
    return 'Error applying discount';
  }
}

此函数验证用户输入的折扣码，处理后调用API更新购物车状态。

2. 移除折扣码

export async function removeDiscount(
  prevState: any,
  payload: {
    discount: string;
    discounts: string[];
  }
) {
  const cartId = cookies().get('cartId')?.value;
  if (!cartId) return 'Missing cart ID';
  
  const code = payload?.discount
  const codes = payload?.discounts ?? []
  
  if (!code) return "Error removing discount. Discount code required.";
  
  let newCodes = codes.filter(item => item !== code);

  try {
    await updateDiscounts(cartId, newCodes);
    revalidateTag(TAGS.cart);
  } catch (e) {
    return 'Error applying discount';
  }
}

此函数从现有折扣码列表中移除指定折扣码，并更新购物车状态。

前端组件实现

1. 折扣码应用表单组件

function SubmitButton(props) {
  const { pending } = useFormStatus();
  
  return (
    <>
      {props.message && (
        <Alert className="my-5" variant="destructive">
          <ExclamationTriangleIcon className="mr-2 h-4 w-4" />
          <AlertTitle>{props.message}</AlertTitle>
        </Alert>
      )}
      {pending ? "" : <input type="text" name="discountCode" placeholder="Discount code" required />}

      <button
        onClick={(e) => { if (pending) e.preventDefault(); }}
        aria-label="Add Discount Code"
        aria-disabled={pending}
      >
        <div className="w-full">
          {pending ? <LoadingDots className="bg-secondary text-white mb-3" /> : null}
        </div>
        {pending ? '' : 'Apply Discount'}
      </button>
    </>
  );
}

export function ApplyCartDiscount({ cart }) {
  const [message, formAction] = useFormState(applyDiscount, null);
  const filteredCodes = cart?.discountCodes?.filter(code => code.applicable).map(code => code.code) || [];

  return (
    <>
      {filteredCodes.length > 0 ? (
        <div>
          {filteredCodes.map((code, index) => (
            <Badge key={index} variant="secondary">
              <TagIcon className="mr-2 inline-block h-5 w-5" />
              {code}
              <DeleteDiscountButton item={code} items={filteredCodes}/>
            </Badge>
          ))}
        </div>
      ) : (
        <form action={formAction}>
          <SubmitButton message={message} />
          <p aria-live="polite" className="sr-only" role="status">
            {message}
          </p>
        </form>
      )}
    </>
  );
}

2. 折扣码移除按钮组件

function SubmitButton() {
  const { pending } = useFormStatus();

  return (
    <button
      type="submit"
      onClick={(e) => { if (pending) e.preventDefault(); }}
      aria-label="Remove Discount"
      aria-disabled={pending}
    >
      {pending ? (
        <LoadingDots className="bg-primary" />
      ) : (
        <XCircleIcon className="mx-5 text-primary hover:border-neutral-800 hover:opacity-80 h-5 w-5" />
      )}
    </button>
  );
}

export function DeleteDiscountButton({ item, items }) {
  const [message, formAction] = useFormState(removeDiscount, null);
  const payload = { discount: item, discounts: items };
  const actionWithVariant = formAction.bind(null, payload);

  return (
    <form action={actionWithVariant}>
      <SubmitButton />
      <p aria-live="polite" className="sr-only" role="status">
        {message}
      </p>
    </form>
  );
}