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class Beverage(models.Model):
    name=models.CharField(max_length=255)

    def __unicode__(self):
        return self.name

class Location(models.Model):
    name=models.CharField(max_length=255)
    beverages = models.ManyToManyField(Beverage, through='LocationStandard')
    location_number=models.CharField(max_length=255)
    organization=models.CharField(max_length=255)

    def __unicode__(self):
        return self.name

class LocationStandard(models.Model):
    beverage=models.ForeignKey(Beverage)
    location=models.ForeignKey(Location) #elim this or m2m
    start_units=models.IntegerField()
    fill_to_standard=models.IntegerField(max_length=10)
    order_when_below=models.IntegerField(max_length=10)

class Order(models.Model):
    location=models.ForeignKey(Location) #elim this or m2m
    beverage=models.ForeignKey(Beverage)
    units_ordered=models.IntegerField(max_length=10, default=0)
    order_delivered=models.BooleanField(default=False)
    timestamp=models.DateTimeField(auto_now_add=True)
    user=models.ForeignKey(User)

如何生成一个报告，该报告将为我提供一个 HTML 表格，其中 x 轴上的所有位置和 y 轴上的所有饮料。我正在努力解决的主要问题就是要查询什么，我可以传递可以循环的模板。想法？

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1 回答 1

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你不能在一个查询中得到它们，但你可以做类似的事情（不想设置整个环境来测试，所以用它作为线索，而不是一个有效的解决方案）：

# you can't do order_by in a template, either do them in the view, or 
# make methods in the model, or make it the Meta default ordering

# print the header, and make sure we got a list of all beverage cached
beverages = Beverage.objects.order_by('name') 
for beverage in beverages:
   print each cell of your header

# print a row for each location
locations = Location.objects.all()
for location in locations:
   print the location name table cell
   location_beverages = iter(location.beverages.order_by('name'))
   # for each beverage, we print a cell. If the beverage is in the 
   # location beverage list, we print a checked cell
   # we use the fact that queryset are iterable to move the cursor
   # only when there is a match
   cur_bev = location_beverages.next()
   for beverage in beverages:
        if beverage == cur_bev:
            print checked table cell
            cur_bev = location_beverages.next()
        else:
            print empty table cell

存储查询集的中间变量非常重要，因为它们允许您从 Django 查询集缓存中受益。

使用 Django 1.4 或更高版本，您可以替换：

locations = Location.objects.all()

经过：

locations = Location.objects.prefetch_related('beverages')

获得严重的性能提升。

于 2012-05-30T00:51:26.753 回答