Django将自己传递给models.SET on_delete [英] Django pass self to models.SET on_delete
问题描述
当我从数据库中删除时,我想修改一个外键值。所以我看了文档,并使用了on_delete = models.SET(foo)方法。 https://docs.djangoproject.com /en/dev/ref/models/fields/#django.db.models.SET
I want to modify a foreign key value when its deleted from the database. So I looked upon the doc and used on_delete=models.SET(foo) method. https://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.SET
这是我的模型定义
class OrderLine(models.Model):
product = models.ForeignKey(Product, on_delete=models.SET(getDuplicateProduct), null=True)
quantity = models.PositiveSmallIntegerField(default=1)
finalPricePerUnit = models.PositiveIntegerField()
order = models.ForeignKey(Order, on_delete=models.PROTECT)
dateCreated = models.DateTimeField(auto_now=False, auto_now_add=True)
这是我的删除方法
def getDuplicateProduct(orderline):
productToDelete = orderline.product
# some logic to generate duplicate copy and returning it
然而,这里的问题是我可以牛逼传递参数,这种方法这就是为什么我不知道哪些产品已被删除。我也尝试使用此答案中指定的信号 django model on_delete pass self to models.SET()
However the problem here is that I can't pass argument to this method which is why I cannot know which product was deleted. I also tried using signals as specified in this answer django model on_delete pass self to models.SET()
我也尝试使用信号,但也没有工作。我似乎无法找出这一个妥善的解决办法。
如果有人想知道如何实现这一点,请告诉我。
I also tried using signals, but that also didn't work. I can't seem to find out a proper solution for this. Let me know if someone has an idea on how to achieve this.
编辑
是我在信号中使用的代码
This is the code I am using in signals
@receiver(pre_delete, sender=Product)
def getDuplicateProduct(sender, **kwargs):
product = kwargs['instance']
orderlines = product.orderline_set.all()
#further processing
现在的问题是django也试图删除我的订单行(默认的on_delete设置为级联)。如果将on_Delete设置为SET_NULL,则将外键设置为null。
Now the problem is that django tries to delete my orderlines as well (as default on_delete is set to cascade). And if I set the on_Delete to SET_NULL, it sets the foreign key to null.
编辑-2
这是我使用的代码
EDIT -2 Here is the code I am using
@receiver(pre_delete, sender=Product)
def getDuplicateProduct(sender, **kwargs):
product = kwargs['instance']
orderlines = product.orderline_set.all()
product.name = product.name + ' ' + product.get_type_display()
newProduct = deepcopy(product)
newProduct.name = product.name + ' ' + product.get_type_display()
newProduct.pk=None
newProduct.id=None
newProduct.save()
product.duplicateProductId = newProduct.id
product.old_orderlines = orderlines
product.save()
@receiver(post_delete, sender=Product)
def handlePostDelete(sender, **kwargs):
product = kwargs['instance']
newProduct = Product.objects.get(id=product.duplicateProductId)
for orderline in product.old_orderlines:
orderline.product = newProduct
orderline.save()
EDIT-3
发布完整的实施完整性。
EDIT-3 Posting full implementation for completeness.
@receiver(pre_delete, sender=Product)
def handlePreDelete(sender, **kwargs):
product = kwargs['instance']
orderlines = product.orderline_set.all()
shouldCreate=False
for orderline in orderlines:
if orderline.order.status>1:
shouldCreate=True
product.shouldCreate = shouldCreate
if shouldCreate:
product.old_orderlines = orderlines
product.save()
else:
product.save()
return None
@receiver(post_delete, sender=Product)
def handlePostDelete(sender, **kwargs):
product = kwargs['instance']
shouldCreate = product.shouldCreate
if shouldCreate:
newProduct = deepcopy(product)
newProduct.name = product.name + ' ' + product.get_type_display()
newProduct.pk=None
newProduct.id=None
newProduct.save()
# Do whatever you want with product.old_orderlines
for orderline in product.old_orderlines:
orderline.product = newProduct
orderline.save()
推荐答案
信号是正确的方法。
您可以获得 OrderLine
从信号接收器:
You can get the OrderLine
from the signal receiver:
@receiver(pre_delete, sender=Product)
def getDuplicateProduct(sender, **kwargs):
product = kwargs['instance']
orderlines = product.orderline_set.all()
# orderlines contains all the OrderLines foreign keyed to the product.
orderlines
是一个可以迭代的查询或批量更新。
orderlines
is a queryset which you can iterate over or update in bulk.
编辑
结论上面提出的方法将无法正常工作,因为在 pre_delete
signal已经触发Django已经确定了需要使用 on_delete
处理的相关模型,并将覆盖这些更改。
Turns out the approach suggested above will not work, because by the time the pre_delete
signal has fired Django has already determined which related models it needs to process with on_delete
, and will overwrite these changes.
这种方法可以起作用,虽然有点笨重:
This approach will work, though it is a bit clunky:
首先,在 pre_delete
收件人:
从副本导入副本
First, in a pre_delete
receiver:
from copy import copy
@receiver(pre_delete, sender=Product)
def handlePreDelete(sender, **kwargs):
product = kwargs['instance']
# Store the OrderLines as a property of the object
# Have to copy it otherwise it will be empty later
product.old_orderlines = copy(product.orderline_set.all())
然后,在$ code> post_delete receive:
Then, in a post_delete
receiver:
@receiver(post_delete, sender=Product)
def handlePostDelete(sender, **kwargs):
product = kwargs['instance']
# Do whatever you want with product.old_orderlines
for line in product.old_orderlines:
# ...
在这两个事件之间,Django将执行 SET_NULL
(或任何你配置的)在OrderLines。
In between these two events, Django will have performed SET_NULL
(or whatever you configured) on the OrderLines.
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