How to return last comment?-CodePudding

I have probably a small problem. Namely how can i extract a last comment when i use 'post.comments.all'

class CommentPost(models.Model):
      user = models.ForeignKey(Profil, on_delete=models.CASCADE)
      post = models.ForeignKey(Posty, on_delete=models.CASCADE, related_name="comments")
      content1 = models.TextField(max_length=250, blank=False, null=False)
      date_posted = models.DateTimeField(default=timezone.now)
      date_updated = models.DateTimeField(auto_now=True)

def __str__(self):
    return str(self.content1)


class Posty(models.Model):
   title = models.CharField(max_length=250, blank=False, null=False, unique=True)
   sub_title = models.SlugField(max_length=250, blank=False, null=False, unique=True)
   content = models.TextField(max_length=250, blank=False, null=False)
   image = models.ImageField(default="avatar.png",upload_to="images", validators=[FileExtensionValidator(['png','jpg','jpeg'])])
   author = models.ForeignKey(Profil, on_delete=models.CASCADE)
   updated = models.DateTimeField(auto_now=True)
   published = models.DateTimeField(auto_now_add=True)
   T_or_F = models.BooleanField(default=False)
   likes = models.ManyToManyField(Profil, related_name='liked')
   unlikes = models.ManyToManyField(Profil, related_name='unlikes')
   created_tags = models.ForeignKey('Tags', blank=True, null=True, related_name='tagi', on_delete=models.CASCADE)

Views

    tag = request.GET.get('tag')
if tag == None:
    my_tag = Posty.objects.all
    print(my_tag)
else:
    my_tag = Posty.objects.filter(created_tags__tag=tag)
    print(my_tag)

If i tried use '[:1]' or last, this dont work.

CodePudding user response：

You can get the last comment with:

post.comments.latest('date_posted')

or if you want the latest per date_updated, you use:

post.comments.latest('date_updated')

If you want to obtain the last comment per post, you can work with a Prefetch object:

from django.db.models import OuterRef, Subquery

posts = Posty.objects.annotate(
    latest_comment=Subquery(
        CommentPost.objects.filter(
            post=OuterRef('pk')
        ).values('content1').order_by('-date_posted')[:1]
    )
)

then in the template, you can render with:

{% for post in posts %}
    {{ post.last_comment }}
{% endfor %}