db_index=True, on_delete=models.SET_NULL, editable=False)
dc = models.JSONField(null=True, editable=False)
cover = models.FileField(blank=True, upload_to='documents/cover')
db_index=True, on_delete=models.SET_NULL, editable=False)
dc = models.JSONField(null=True, editable=False)
cover = models.FileField(blank=True, upload_to='documents/cover')