Question

I have two models like so:

class Visit(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=65535, null=False)

class Session:
    id = models.AutoField(primary_key=True)
    visit = models.ForeignKey(Visit)
    sequence_no = models.IntegerField(null = False)

---

I’d like two write a custom create method in the Session model so when I write this:

visitor = Vistor.objects.get(id=1)
new_session = Session.objects.create_new_session(visit=visitor)

…I get a new record in the Session table with the next consecutive sequence number for that visitor i.e. 3. Here’s some sample data

VISITOR SEQUENCE_NO
------- -----------
1         1
1         2
2         1
2         2
1         3 (This would be the row that would be created)

---

The other was writing a custom get method in the Session model so that I write:

visitor = Vistor.objects.get(id=1)
new_session = Session.objects.get_session(visit=visitor, sequence_no=3)

…I get the previous record of that visitor with the highest sequence number. Here’s some sample data

VISITOR SEQUENCE_NO
------- -----------
1         1
1         2 (This would be the row that would be fetched)
2         1
2         2
1         3 

---

Could you tell me how to accomplish this please? Should this code be in the Model or the Manager?

Thanks everyone.

Answer 1

This would be in a Manager for Sessions. It would look something like (untested):

class SessionManager(models.Manager):
    def new_session(self, visit, **kwargs):
        vs = self.model.objects.filter(visit=visit).order_by("-sequence_no")[:1]
        if len(vs):
            kwargs.update({"sequence_no": vs.sequence_no + 1})
        return Super(SessionManager, self).create(visit=visit, **kwargs)

As for getting a session when you have visit, and sequence_no there shouldn’t be any custom code needed for that.