Kim Majali

Django Annotate() and Alias()

Kim Majali wrote on 06/06/2022

Channel

class VideoChannel(models.Model):
    user=models.ForeignKey(User,on_delete=models.CASCADE)
    name=models.CharField(max_length=200)
    detail=models.TextField()
    def __str__(self):
        return self.name

Order By

Kim Majali wrote on 06/06/2022

Regular

Author.objects.order_by('name')

Related Model

Book.objects.order_by('author__name')

Reverse

Author.objects.order_by('-name')

Multiple Fields

Author.objects.order_by('-name', 'city')

Random Ordering

Author.objects.order_by('?')

Case Sensitive

Author.objects.order_by(Lower('name'))

No Ordering

Author.objects.order_by()

Overriding Order By

Author.objects.order_by('name').order_by('city')

Reverse

queryset = my_queryset.reverse()[:5]

Distinct

queryset = Author.objects.distinct()

Select_Related() Prefetch_Related()

Kim Majali wrote on 06/06/2022

When the database has foreign keys, using select_related() and prefetch_related() can reduce the number of database requests and improve performance

Avoid Resubmitted Form Upon Refresh

Kim Majali wrote on 06/06/2022

After successful submission and processing of a web form, you need to use a return HttpResponseRedirect

def some_view(request):
  if request.method == "POST":
    form = some_form(request.POST)
    if form.is_valid():

Django Check If Object Or a Value Exists

Kim Majali wrote on 06/06/2022

Record checks

Use exists()

if scorm.objects.filter(Header__id=qp.id).exists(): # does not work with get