在 django 中通过一个查询获取多行？
如何构建一个从 django 获取多行的查询集？我认为 filter() 会起作用，但它似乎更糟。
例如，我在模型 Car 中有两行，具有两个文本属性（许可证和 vin）。现在假设我想打印这些汽车的执照和车辆证明。我怎样才能通过一次数据库调用来做到这一点？
这是一个将进行两次数据库调用的答案：
#using get(), two total queries
a = Car.objects.get(id=1) #query here
b = Car.objects.get(id=2) #query here
print(a.license + a.vin) #no query
print(b.license + b.vin) #no query
这显然不起作用，因为我进行了两次 get() 查询。接下来我将尝试 filter()：
#using filter(), four total queries
c = Car.objects.filter(id__in=(1,2)) #no query
print(c[0].license + c[0].vin) #two queries
print(c[1].license + c[1].vin) #two queries
嗯，这很奇怪，为什么要进行四个数据库调用？有没有办法让它获得二合一数据库调用？
How can I get build a QuerySet that gets multiple rows from django? I thought filter() would work, but it seems to be worse off.
For example, I have two rows in the model Car, with two text attributes (license and vin). Now say I want to print the licenses and vins from these cars. How can I do that with one database call?
Here's an answer that will make two database calls:
#using get(), two total queries
a = Car.objects.get(id=1) #query here
b = Car.objects.get(id=2) #query here
print(a.license + a.vin) #no query
print(b.license + b.vin) #no query
That obviously didn't work because I made two get() queries. So next I'll try filter():
#using filter(), four total queries
c = Car.objects.filter(id__in=(1,2)) #no query
print(c[0].license + c[0].vin) #two queries
print(c[1].license + c[1].vin) #two queries
Hmmm, that's weird, why is making four database calls? Is there a way I can make it get the two in one database call?
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由于查询集索引的工作方式，这看起来很奇怪。
如果您执行以下操作，您也只会有一个查询：
正如@Torsten 所说，在您的情况下，您似乎只是想获取您创建的所有汽车。这可以通过
all()方法来实现：It's seems weird because of how indexing into a queryset works.
If you do the following, you'll only have one query too:
As @Torsten said, in your situation it appears like you're simply trying to get all the cars you've created. This can be achieved via the
all()method:很好的例子。我认为在你的最后一个代码块中存在拼写错误。应该是：
该方法如何叠加
Great example. A typo I think though in your last codeblock. Should be:
How does that method stack up