Best way to make "viewed" attribute for messages inside user group? - django

Question

I am deciding on how to track if a user has seen a post in the timeline or not.
There is Post and Comment model like this.
class Comment(models.Model):
author = models.ForeignKey('UserProfile')
title = models.CharField(max_length=255)
text = models.TextField(null=True, blank=True)
date_created = models.DateTimeField()
post = models.ForeignKey('Post', related_name='comments')
class Post(ContentTypeModel):
title = models.CharField(max_length=255)
group = models.ForeignKey('UserGroup', null=True)
date_updated = models.DateTimeField()
Suggestions about best practices on how to track if post has been seen by particular member of a user group will be nice.

Answer 1

I managed to do as was suggested, i.e. adding m2m relation to track who viewed the post:
class Post(models.Model):
...
date_updated = models.DateTimeField()
viewers = models.ManyToManyField('UserProfile', through='PostViewer')
class PostViewer(models.Model):
post = models.ForeignKey(Post, on_delete=models.CASCADE)
viewer = models.ForeignKey('UserProfile', on_delete=models.CASCADE, related_name='posts_seen')
last_seen = models.DateTimeField(null=True, blank=True, help_text='Is set when user sees the post in details')
class Meta:
unique_together = ('post', 'viewer')
This way i can compare post.date_updated to viewer.last_seen and get desired filtering on who have seen the update/create of Post.