遍历组，然后逐项循环

Question

Django 1.11.4

PostgreSQL 9.6.3

Below is a bookmark model.

class Bookmark(CommonUrlMethodsMixin,
               models.Model):
    memo = models.CharField(max_length=200,
                            null=False,
                            blank=True,
                            default="")  # Intentionally blank.
                                              # For displaying in ModelForm.

    content_type = models.ForeignKey(ContentType)
    content_type_for_filter = models.CharField(max_length=6,
                            null=False,
                            blank=True,
                            default="")
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')
    user = models.ForeignKey(User,
                             on_delete=models.CASCADE)

    def __str__(self):
        return "{}: {} {}".format(self.content_object._meta.verbose_name.title(), self.content_object, self.memo)

    class Meta:
        verbose_name = _("bookmark")

In my project bookmarked can be a Frame, an Item, a Sheet. So, I organized a special field in the Bookmark model content_type_for_filter. It may contain either "frame", or "item" or "sheet".

Bookmarks must be shown in groups: first bookmarks for Frames, then for Items and lastly for Sheets:

Frames
     bookmark 1
     bookmark 2
     bookmark 3
Sheets
     bookmark 4
     bookmark 5
Items
     bookmark 6
     bookmark 7
     bookmark 8

Then in the personal area I'd like to show the bookmarks. In views now I have:

def get_context_data(self, **kwargs):
    bookmarks = user.bookmark_set.all()
    # context['bookmarks'] = bookmarks

It seems that my code is not acceptable. Look: I will have to handle bookmarks somehow in Python. Use a named tuple or something. Or at least three lists of lists.

I suppose, that my select from the data base is not optimal. Is suppose, it may be possible to group by "content_type_for_filter". Then loop through groups. And then loop through the contents of the groups. But I don't know how.

Could you help me understand how to do that? Is it possible with ORM? If not, how to do that without ORM?

Answer 1

My suggestion is that you further filter your bookmarks queryset and put it inside a dict or another class that better suit your needs:

bookmarks = user.bookmark_set.all()
from collections import OrderedDict as odict
groups = odict()
for group in ['Frames', 'Sheets', 'Itens']:
    groups[group] = bookmarks.filter(content_type_for_filter=group)
context['groups'] = groups

An more advanced option could be aggregating your queryset. AFAIK, it groups only values and/or annotations, but I could be wrong.

First of all, you need to define a context:

 
 
 
  
  def get_context_data(self, **kwargs): context = super(<YOUR VIEW NAME>, self).get_context_data(**kwargs)
 
  

Then, it seems you didn't defined an user. You may define it as follows

 
 
 
  
  # current user context['bookmarks'] = self.request.user.bookmark_set.all() # using an user specified in kwargs user = get_object_or_404(User, kwargs.get('user_pk')) # or, if your view is a DetailView of User user = self.get_object() # then, finally context['bookmarks'] = Bookmarks.objects.filter(user=user)