Python django中的查询优化

我想使用django orm优化循环代码，因为它需要41个查询，因为循环显示在django调试工具栏中，我已经用django orm说明了我的模型，有一个循环，我需要使用orm方法进行优化，以避免循环

class Bills(models.Model):
    library=models.ForeignKey(Library,null=True)
    customer=models.ForeignKey(Customer, null=True)
    total_price = models.FloatField()
    History = '1'
    Physics = '2'
    Maths = '3'
    Book_Category=(
        (History,'History'),
        (Physics,'Physics'),
        (Maths,'Maths')
    )
    book_category_type=models.CharField(max_length=2,choices=Book_Category)

这是存储特定客户的所有账单的账单模型

class LibraryOrder(models.Model):
   hotel=models.ForeignKey(Hotel,null=True)
   library = models.ForeignKey(Library,null=True)
   customer=models.ForeignKey(Customer,null=True)
   library_item = models.ForeignKey(LibraryItem,null=True)
   quantity = models.FloatField()
   total_price = models.FloatField()
   comments=models.TextField(null=True)
   bill=models.ForeignKey(Bills,null=True)
   ORDER_STATUS = (
      (NOT_PROCESSED, 'NotProcessed'),
      (PROCESSING, 'Processing'),
      (PROCESSED,'processed'),
   )
   order_status = models.CharField(max_length=3, choices=ORDER_STATUS, default=NOT_PROCESSED)

这是当一些客户订购图书馆项目中的某些书籍时的订单模型

现在我用的是：

customers = Customer.objects.filter(library="1").exclude(customer_status='2')
bills = Bills.objects.filter(library="1", customer=customers, book_category_type="1")
for bill in bills:
    # if bill.order_type == "1":
    not_processed_order = LibraryOrder.objects.filter(bill=bill, order_status="1")
    notprocessed_lists.append(not_processed_order)
    processing_order = LibraryOrder.objects.filter(bill=bill, order_status="2")
    processing_lists.append(processing_order)
    processed_order = LibraryOrder.objects.filter(bill=bill, order_status="3")
    processed_lists.append(processed_order)

正在循环的账单是通过orm获取账单数组的循环，就像在图书馆订单中，我使用账单作为外键获取订单详细信息，并推送到数组中以在html中显示一样

---

我想优化django orm方法，我已经指定将两行转换为单行，这些列表是单独的，因为它显示在html的单独选项卡中。在这个特定场景中，您可以使用与自定义

预回迁

对象相关的

预回迁来预回迁必要的数据，而不在循环内进行任何查询

customers = Customer.objects.filter(library="1").exclude(customer_status='2')
bills = Bills.objects.filter(library="1", customer=customers, book_category_type="1").prefetch_related(
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="1"), to_attr='not_processed_orders'),
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="2"), to_attr='processing_orders'),
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="3"), to_attr='processed_orders'),
    )

for bill in bills:
    notprocessed_lists.append(bill.not_processed_orders)
    processing_lists.append(bill.processing_orders)
    processed_lists.append(bill.processed_orders)

这样，您将有3个查询（每个
prefetch
对象1个查询），而不是40多个查询

您可以进一步优化if到1个查询，但是您必须在python代码中做更多的工作：

customers = Customer.objects.filter(library="1").exclude(customer_status='2')
bills = Bills.objects.filter(library="1", customer=customers, book_category_type="1").prefetch_related('libraryorder_set')

for bill in bills:
    not_processed_orders = []
    processing_orders = []
    processed_orders = []
    for order in bill.libraryorder_set.all():
        if order.status == '1':
            not_processed_orders.append(order)
        elif order_status == '2':
            processing_orders.append(order)
        elif order_status == '3':
            processed_orders.append(order_status)
    notprocessed_lists.append(bill.not_processed_orders)
    processing_lists.append(bill.processing_orders)
    processed_lists.append(bill.processed_orders)

然而，为了学习如何钓鱼，我建议您阅读以下文档中的文章：






在此特定场景中，您可以将
prefetch\u related
与自定义
prefetch
对象一起使用，以预取必要的数据，而不在循环内进行任何查询

customers = Customer.objects.filter(library="1").exclude(customer_status='2')
bills = Bills.objects.filter(library="1", customer=customers, book_category_type="1").prefetch_related(
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="1"), to_attr='not_processed_orders'),
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="2"), to_attr='processing_orders'),
        Prefetch('libraryorder_set', queryset=LibraryOrder.objects.filter(order_status="3"), to_attr='processed_orders'),
    )

for bill in bills:
    notprocessed_lists.append(bill.not_processed_orders)
    processing_lists.append(bill.processing_orders)
    processed_lists.append(bill.processed_orders)

这样，您将有3个查询（每个
prefetch
对象1个查询），而不是40多个查询

您可以进一步优化if到1个查询，但是您必须在python代码中做更多的工作：

customers = Customer.objects.filter(library="1").exclude(customer_status='2')
bills = Bills.objects.filter(library="1", customer=customers, book_category_type="1").prefetch_related('libraryorder_set')

for bill in bills:
    not_processed_orders = []
    processing_orders = []
    processed_orders = []
    for order in bill.libraryorder_set.all():
        if order.status == '1':
            not_processed_orders.append(order)
        elif order_status == '2':
            processing_orders.append(order)
        elif order_status == '3':
            processed_orders.append(order_status)
    notprocessed_lists.append(bill.not_processed_orders)
    processing_lists.append(bill.processing_orders)
    processed_lists.append(bill.processed_orders)

然而，为了学习如何钓鱼，我建议您阅读以下文档中的文章：