Question

I’m trying to create a custom function in a model manager:

class MessageManager(models.Manager):
    # Return body from last child message
    def get_last_child_body(self):
        if self.has_childs:
            last_child = self.filter(parent_msg=self.id).order_by('-send_at')[0]
            return last_child.body

I want to use this function (“get_last_child_body”) in template

{% message.get_last_child_body %}

to retrieve the body from the last child message inserted in table message.

The Message model:

class Message(models.Model):
    sender = models.ForeignKey(User, related_name='sent_messages')
    recipient = models.ForeignKey(User, related_name='received_messages')
    parent_msg = models.ForeignKey('self', related_name='next_messages', null=True, blank=True)
    has_childs = models.BooleanField()
    subject = models.CharField(max_length=120)
    body = models.TextField()
    send_at = models.DateTimeField()
    read_at = models.DateTimeField(null=True, blank=True)
    replied_at = models.DateTimeField(null=True, blank=True)
    sender_deleted_at = models.DateTimeField(null=True, blank=True)
    recipient_deleted_at = models.DateTimeField(null=True, blank=True)

    objects = MessageManager()

    def get_last_child(self):
        if not self.has_childs:
            return None

    class Meta:
        get_latest_by = 'send_at'
        ordering = ['-send_at']

Well, I’m guessing the problem is located in “id” from custom function in manager. I have to pass the parent message id but i don’t know how can i do it.

It does not report any error, it just does not show anything in template.

Any ideas?

Answer 1

Managers should be used for Model specific operators. Here however you are doing an instance specific operation so the get_last_child_body should be inside your Message class.

In comments you mentioned you tried to move it. It should work, something else is probably wrong. You should verify that:

1. message is defined in the template (use if template tag for example to log result )
2. get_last_child_body gets called (use print statements for example)
3. keep on debugging deeper is still no result (print statements work if it’s easiest for you)