How to override "Cannot asign must be an instance" in Django?-CodePudding

I have two models:

class Message(models.Model):
    username = models.CharField(max_length=255)
    room = models.CharField(max_length=255)
    content = models.TextField()
    date_added = models.DateTimeField(auto_now_add=True)

class Notification(models.Model):
    notification_author = models.ForeignKey(Profile, on_delete=models.CASCADE, related_name="notifauthor")
    notification_from = models.ForeignKey(Order, on_delete=models.CASCADE, related_name="notiffrom")
    is_read = models.BooleanField(default=False)

signals:

@receiver(post_save, sender=Message)

def create_user_notification(sender, instance, created, **kwargs):
    if created:
        Notification.objects.create(
                                    notification_author=instance.username,
                                    notification_from=instance.room)

@receiver(post_save, sender=Message)
def save_user_notification(sender, instance, **kwargs):
    instance.username.save()

I am trying to create signal for creating notification after message is created. But have error:

Cannot assign "20": "Notification.notification_author" must be a "Profile" instance.

How to override it (if possible) without changing CharField to FK in Message model?

Found smth about eval(), but it does not still work

CodePudding user response：

The question is how to convert the string to Profile model without using FK

notification_author=Profile.objects.get_or_create(username=instance.username)