Why the first() method and slices works differently in Django?

Question

I have the model:

class PhotoAlbum(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False, auto_created=True)
    name = models.CharField(max_length=50, verbose_name='Album name')
    type = models.ForeignKey(AlbumType, on_delete=models.CASCADE, verbose_name='Album type')
    created_at = models.DateTimeField(auto_now_add=True)

And i have this code:

print(PhotoAlbum.objects.all().first())
print(PhotoAlbum.objects.all()[:1].get())

it seemed to me that the same objects should be displayed, but different ones are returned.

What’s going on, isn’t it an identical design?

Asked By: Anonymous Wizard

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Source

Answer 1

If the queryset is not ordered then first() orders the queryset by the primary key so:

from django.db import connection
Pet.objects.all().first()
print(connection.queries[-1]['sql'])
# SELECT ... FROM <table> ORDER BY <table>."id" ASC LIMIT 1

But slicing the queryset performs no such default ordering.

from django.db import connection
Pet.objects.all()[:1].get()
print(connection.queries[-1]['sql'])
# SELECT ... FROM <table> ASC LIMIT 1

Answered By: Iain Shelvington

Why the first() method and slices works differently in Django?

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