python - 迭代具有相同属性的所有查询结果的巧妙方法

Question

假设:

class ItemToBill(models.Model):
    date_to_bill = fields.DateField()
    description = fields.charfield()
    customerToBill = fields.ForeignKey(Customer)

我想找到今天之前应计费的所有项目，然后按客户对它们进行分组，以便我可以为每个需要的客户创建一张发票。

for unique_customer in all_unique_customers_with_items_to_bill:
    createInvoice(unique_customer,  their_items_to_bill)

我可能可以做一些事情，查询商品(由客户订购)，然后确定何时输入新客户的商品集。这看起来像:

items = ItemToBill.objects.filter(date_to_bill=BEFORE_TODAY).order_by(customer)
prevCustomer = items[0].customer
customer_items = []
for item in items:
    if prevCustomer != item.customer:
        createInvoice(prevCustomer, customer_items)
        customer_items = []
        prevCustomer = item.customer
    customer_items.append(item)
createInvioce(prevCustomer, customer_items) #Handle the last customer

但是必须有一个更聪明的解决方案。有建议吗？

Answer 1

您需要客户的商品列表，这听起来像是一个简单的循环。

items_by_customer = {}

for item in ItemToBill.objects.filter(...date_query...):
    items_by_customer.setdefault(item.customerToBill, []).append(item)

for customer, items in items_by_customer.items():
    print customer, items # items grouped by customer.
    # generate_invoice(customer, items)