class Post(models.Model):
title = models.CharField(max_lenth=50)
next_posts = models.ManyToManyField('self', related_name='prev_posts', blank=True)
class Post(models.Model):
title = models.CharField(max_lenth=50)
next_posts = models.ManyToManyField('self', related_name='prev_posts', symmetrical=False, blank=True)