Data modeling suggestions for Django app - django

Question

I have a Django app where users leave comments for each other. I'm now going to add a photo feature. I need some help in formulating the data model(s) for this photo feature.
Under this feature, users will be able to upload photos in a common area of the website, where the said photos will appear most-recent first. This is simple enough, so let's now add two complications to the feature:
1) For each photo entry, uploaders will have the option of including
additional photos (as a stream). The first photo will then be treated
as a cover photo that is shown in the common area of the website. Upon
clicking this cover, the entire stream will become visible.
2) For each photo entry, any viewer will be able to reply with a
photo of their own. If that happens, the two photos will be put
together as a stream, with the reply treated as a cover photo, to
appear in the common area of the website. Clicking this cover photo
will show both entries one after the other, thus showing the users
what the original photo was, and what the reply to it was.
How should I model the above requirements? I can't seem to wrap my head around this. Something like:
class PhotoReply(models.Model):
owner = models.ForeignKey(User)
which_photo = models.ForeignKey(Photo)
class Photo(models.Model):
owner = models.ForeignKey(User)
is_stream = models.BooleanField(default=False)
image = models.ForeignKey(upload_to=upload_photo_to_location, storage=OverwriteStorage())
upload_time = models.DateTimeField(db_index=True, auto_now_add=True)
stream_id = models.IntegerField(default=0)
is_reply = models.BooleanField(default=False)
reply = models.ForeignKey(PhotoReply, blank=True, null=True)
But there are obvious weakness, inconsistencies in that. Please advise.

Answer 1

Did I understand you correctly that every photo can become a "cover photo", as soon as a user replies to it with another photo? If that's the case, then you only need to keep track of the "children" that a photo has, to know if you want to display it as "cover" or not.
class Photo(models.Model):
owner = models.ForeignKey(User)
parent = models.ForeignKey('self', db_index=True, null=True, default=None)
child_count = models.IntegerField(default=0, db_index=True)
image = models.ForeignKey(upload_to=loc)
upload_time = models.DateTimeField(db_index=True)
So a photo that has > 0 children is a "cover". And for each "cover" photo "x" you just need to look to look up all photos that have "x" as a parent.