How to Create an Auto Increment in Django that is not pk

Question

I’m creating a memo system with Django and it’s working fine, but I need to put in a self-improvement field that’s not pk. I have this field in my models.

Memo = models.IntegerField()

I need it already receive the value or the id or a counter, I am using python3 and Django 11.

If anyone can give me a light thank you!

Answer 1

You can use the Django-Sequence-field. Take an example from him:

from sequence_field.fields import SequenceField

# Create your models here.

class TestModel(models.Model):

    sequence = SequenceField(
        key='test.sequence.1',
        template='%Y%m%d%(code)s%NNNNN',
        params={'code':'ABC'},
        auto=True
    )

Testing the Model

from my_app.models import TestModel

obj = TestModel()
obj.save()

print obj.sequence # 20140703ABC00001

obj = TestModel()
obj.save()

print obj.sequence # 20140703ABC00002

Alternative

You can do this validation by hand yourself too:

def next_sequence():
    _model = Memorando.objects.filter().order_by('-Memo')[:1]
    if _model.count() > 0:
        return int(_model[0].Memo) + 1
    return 0

Answer 2

Edited
It seems that the original solution does not work, Django (v. 1.11) requires an autofield field to have the parameter primary_key=True, an error, in my view, for what is the parameter? The way is to try to remedy with a function, see if it works, the function can be put in the file itself models or in another separate file (as long as you import it in models.py)

import datetime
def increment_chamado():
    ultimo = Chamado.objects.all().order_by('id').last()
    if not ultimo:
        return str(datetime.date.today().year) + str(datetime.date.today().month).zfill(2) + '0000'
    ultimo_id = ultimo.chamado_id
    ultimo_int = int(ultimo_id[9:13])
    new_int = ultimo_int+1
    new_id = str(str(datetime.date.today().year)) + str(datetime.date.today().month).zfill(2) + str(new_int).zfill(4)
  return new_id

In models the field that identifies the call would be:

classe Chamado(models.Model):
    chamado_id = models.CharField(max_length = 20, default = 
        increment_chamado, editable=False)

Based on a post from thecstream.org.

From this point on, the answer "original".

Autofield

Integer field with automatic increment, Primary keys use it automatically. A primary key is automatically added to your template if you do not specify it.

If you add to your template:

incremento = models.AutoField(primary_key=False)

You will be adding a field of the type you want (auto-increment) to your model.

SQN

Only... if you haven’t defined a PK of your own autofield, when you try to spin the migrations to add your field to the bank, you will receive the msg:

AssertionError: A model can't have more than one AutoField.

Solution

Define your own PK on a field that is not autofield

Suggestion

If you don’t have a field that can guarantee it unique to use as PK make the PKas being uuid thus:

id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)