I saw this answer but there is no specific answer yet. I want to create custom id that starts with letter. When a new record comes into database I want to change the id to A00001, .... A00002, .... A00010, ...A10000 etc. The id will be always in range 99999- 00001 so how can I do that?
my model is simple:
class Custom(models.Model):
id = models.AutoField(primary_key=True, editable=False)
The AutoField field is a kind of IntegerField field, so you can't use PKs as A00001 .
So, the possible way to achieve the requirement is to change the AutoField to CharField.
Technically you can use "String PK Field" But, you should be aware of the problems/performance issues if you are going to use that.
Here I found one nice SO post that explains the same - Strings as Primary Keys in SQL Database
========================================================================
If you still really wish to migrate to String PKs, read the following
First you need to use the CharField instead of AutoField and override the save() method of model
from django.db.models import Max
class Custom(models.Model):
id = models.CharField(primary_key=True, editable=False, max_length=10)
name = models.CharField(max_length=100)
def save(self, **kwargs):
if not self.id:
max = Custom.objects.aggregate(id_max=Max('id'))['id_max']
self.id = "{}{:05d}".format('A', max if max is not None else 1)
super().save(*kwargs)
string as Primary Key not good idea if you plan to do references to the table, so i recommend you to add a property, for example:
class Custom(models.Model):
id = models.AutoField(primary_key=True, editable=False)
@property
def sid(self):
return "A%05d" % self.id
and to do queries you can do processing the input values, for example:
s_input = "A%05d" % 231 # 'A00231'
number = s_input[1:] # '00231'
input_id = int(number) # 231
I also have another way, That i use in my django project. Here are some code
def ids():
no = Employee.objects.count()
if no == None:
return 1
else:
return no + 1
emp_id = models.IntegerField(('Code'), default=ids, unique=True, editable=False)
id = models.CharField(primary_key=True, editable=False, max_length=30)
def save(self, **kwargs):
if not self.id:
self.id = "{}{:08d}".format('ABC', self.emp_id)
super().save(*kwargs)
It's better to create a new field for the custom id in the models and the process in the backend. You can set that as primary_key with unique=True and editable=False:
class Custom(models.Model):
id = models.Autofield(primary_key=True, editable=False, max_length=10)
uid= models.CharField(max_length=100, unique=True)
def save(self, *args, **kwargs):
super().save(*args, **kwargs)
self.set_uid() # calling the set_uid function
def set_uid(self):
if not self.uid: # if uid of the instance is blank
uid = "CUS" + str(self.id + (10 ** 5)) # generating the uid
customer= Custom.objects.get(id=self.id) # getting the instance
customer.uid = uid # allocating the value
customer.save() # saving the instance
def __str__(self):
return self.uid
Can also merge the set_uid() inside the save() where the function is called:
class Custom(models.Model):
id = models.Autofield(primary_key=True, editable=False, max_length=10)
uid= models.CharField(max_length=100, unique=True)
def save(self, *args, **kwargs):
super().save(*args, **kwargs)
if not self.uid: # if uid of the instance is blank
self.uid = "CUS" + str(self.id + (10 ** 5)) # generating the uid and allocating the value
self.save() # saving the instance
def __str__(self):
return self.uid
I tried to use answer of @JPG, but it has a bug. The bug is becasue it can't auto increment. I fixed the bug, and this my resultant code:
def save(self, **kwargs):
if not self.id:
max = YourModel.objects.aggregate(
id_max=models.Max('id'))['id_max']
if max is not None:
max += 1
else:
max = 100
self.id = "{:08d}".format(
max) # id from 100 to start
super().save(*kwargs)
