How do I make an auto increment integer field in Django?

Question

I am making an Order model for a shopping cart and I need to make a field that auto increments when the order is made:

class Order(models.Model):
    cart = models.ForeignKey(Cart)
    add_date = models.DateTimeField(auto_now_add=True)
    order_number = models.IntegerField()
    enable = models.BooleanField(default=True)

How do I make the IntegerField auto increment?

Answer 1

In Django

1 : Django model class has default field with name id which is auto increment Field.
2 : You can define your own auto increment field using AutoField field.

class Order(models.Model):
    auto_increment_id = models.AutoField(primary_key=True)
    # primary_key = True if you do not want to use default field "id" given by django to your model

db design

+------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table      | Create Table                                                                                                                                                  |
+------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
| core_order | CREATE TABLE `core_order` (
  `auto_increment_id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`auto_increment_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

If you want to use django's default id as increment field .

class Order(models.Model):
    add_date = models.DateTimeField(auto_now_add=True)

db design

+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table       | Create Table                                                                                                                                                    |
+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| core_order | CREATE TABLE `core_order` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `add_date` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+

Answer 2

In django with every model you will get the by default id field that is auto increament. But still if you manually want to use auto increment. You just need to specify in your Model AutoField.

class Author(models.Model):
    author_id = models.AutoField(primary_key=True)

you can read more about the auto field in django in Django Documentation for AutoField

Answer 3

class Belly(models.Model):
    belly_id = models.AutoField(primary_key=True)
    belly_name = models.CharField(max_length=50)

******** or *******

class Belly(models.Model):
   belly_name = models.CharField(max_length=50)

The difference is:

The first table has the primary key belly_id (specified as AutoField) and second table has the primary key id (implicitly).

I think no need to use this directly; a primary key field will automatically be added to your model if you don’t specify. Otherwise Check the Django Documentation for AutoField for further details related to AutoField.

Answer 4

Edited: Fixed mistake in code that stopped it working if there were no YourModel entries in the db.

There's a lot of mention of how you should use an AutoField, and of course, where possible you should use that.

However there are legitimate reasons for implementing auto-incrementing fields yourself (such as if you need an id to start from 500 or increment by tens for whatever reason).

In your models.py

from django.db import models

def from_500():
    '''
    Returns the next default value for the `ones` field,
    starts from 500
    '''
    # Retrieve a list of `YourModel` instances, sort them by
    # the `ones` field and get the largest entry
    largest = YourModel.objects.all().order_by('ones').last()
    if not largest:
        # largest is `None` if `YourModel` has no instances
        # in which case we return the start value of 500
        return 500
    # If an instance of `YourModel` is returned, we get it's
    # `ones` attribute and increment it by 1
    return largest.ones + 1

def add_ten():
    ''' Returns the next default value for the `tens` field'''
    # Retrieve a list of `YourModel` instances, sort them by
    # the `tens` field and get the largest entry
    largest = YourModel.objects.all().order_by('tens').last()
    if not largest:
        # largest is `None` if `YourModel` has no instances
        # in which case we return the start value of 10
        return 10
    # If an instance of `YourModel` is returned, we get it's
    # `tens` attribute and increment it by 10
    return largest.tens + 10


class YourModel(model.Model):
    ones = models.IntegerField(primary_key=True,
                               default=from_500)
    tens = models.IntegerField(default=add_ten)