[Django]-Auto-create primary key used when not defining a primary key type warning in Django

You have unintentionaly updated Django to 3.2 which warns you and as hint text suggest you have to set DEFAULT_AUTO_FIELD as documented
This way you avoid unwanted migrations in future releases as
value of DEFAULT_AUTO_FIELD will be changed to BigAutoField

You should set DEFAULT_AUTO_FIELD explicitly to current DEFAULT_AUTO_FIELD value

DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'

you could configure it even per app basis ( if you expect to build new apps with current style primary key)

from django.apps import AppConfig

class MyAppConfig(AppConfig):
    default_auto_field = 'django.db.models.AutoField'
    name = 'my_app'

or even per-model (discouraged)

from django.db import models

class MyModel(models.Model):
    id = models.AutoField(primary_key=True)

You should also take care of version locking your requirements as you could introduce backward incompatible changes in production

new created project settings.py file in django 3.2
includes this:

..

# Default primary key field type
# https://docs.djangoproject.com/en/3.2/ref/settings/#default-auto-field

DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'

and as your project was created on earlier versions of django so you can append this to your settings.

models.py:
       class Topic(models.Model):
           id = models.AutoField(primary_key=True)

primary_key=True https://docs.djangoproject.com/en/3.2/ref/models/fields/#primary-key

settings.py:
DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'

DEFAULT_AUTO_FIELD https://docs.djangoproject.com/en/3.2/ref/settings/#default-auto-field

A simple solution:

Django wants you to add the serial number that’s called by primary key and if you can ignore this warning then okay django will automatically add the primary key otherwise, if you want to remove this warning then add this code in your defined model:

id = models.AutoField(primary_key=True)

For example:

class Contact(models.Model):
    sno = models.AutoField(primary_key=True)
    name = models.CharField(max_length=25, blank=True)
    email = models.EmailField(max_length=40, blank=True)
    phone = models.IntegerField()

HaPpY Coding