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Creating a Django Report

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)

How can I generate a report that will give me an HTML table with all locations along the x axis and all drinks along the y axis. The main thing I'm struggling with is what I can request in order to pass a pattern that I can iterate over. Thoughts?

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1 answer

You cannot get them in a single request, but you can do something like this (you do not want to configure all env for testing, so use it as a hint, not a working solution):

# 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

Intermediate variables for storing requests are very important because they allow you to retrieve caching of Django requests.

With Django 1.4 or more, you can replace:

locations = Location.objects.all()

By:

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

To get a serious boost.

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