Generate a random alphanumeric string as a primary key for a model

Question

I would like a model to generate automatically a random alphanumeric string as its primary key when I create a new instance of it.

example:

from django.db import models

class MyTemporaryObject(models.Model):
    id = AutoGenStringField(lenght=16, primary_key=True)
    some_filed = ...
    some_other_field = ...

in my mind the key should look something like this “Ay3kJaBdGfcadZdao03293”. It’s for very temporary use. In case of collision I would like it Django to try a new key.

I was wondering if there was already something out there, or a very simple solution I am not seeing (I am fairly new to python and Django). Otherwise I was thinking to do my own version of models.AutoField, would that be the right approach?

I have already found how to generate the key here, so it’s not about the string generation. I would just like to have it work seamlessly with a simple Django service without adding too much complexity to the code.

EDIT:
Possible solution? What do you think?

id = models.CharField(unique=True, primary_key=True, default=StringKeyGenerator(), editable=False)

with

class StringKeyGenerator(object):
    def __init__(self, len=16):
        self.lenght = len
    def __call__(self):
        return ''.join(random.choice(string.letters + string.digits) for x in range(self.lenght))

I came up with it after going through the Django documentation one more time.

Asked By: le-doude

||

Source

Answer 1

One of the simplest way to generate unique strings in python is to use uuid module. If you want to get alphanumeric output, you can simply use base64 encoding as well:

import uuid
import base64
uuid = base64.b64encode(uuid.uuid4().bytes).replace('=', '')
# sample value: 1Ctu77qhTaSSh5soJBJifg

You can then put this code in the model’s save method or define a custom model field using it.

Answered By: Amir Ali Akbari

Answer 2

Here’s how I would do it without making the field a primary key:

from django.db import IntegrityError

class MyTemporaryObject(models.Model):
    auto_pseudoid = models.CharField(max_length=16, blank=True, editable=False, unique=True)
    # add index=True if you plan to look objects up by it
    # blank=True is so you can validate objects before saving - the save method will ensure that it gets a value

    # other fields as desired

    def save(self, *args, **kwargs):
        if not self.auto_pseudoid:
            self.auto_pseudoid = generate_random_alphanumeric(16)
            # using your function as above or anything else
        success = False
        failures = 0
        while not success:
            try:
                super(MyTemporaryObject, self).save(*args, **kwargs)
            except IntegrityError:
                 failures += 1
                 if failures > 5: # or some other arbitrary cutoff point at which things are clearly wrong
                     raise
                 else:
                     # looks like a collision, try another random value
                     self.auto_pseudoid = generate_random_alphanumeric(16)
            else:
                 success = True

Two problems that this avoids, compared to using the field as the primary key are that:

1) Django’s built in relationship fields require integer keys

2) Django uses the presence of the primary key in the database as a sign that save should update an existing record rather than insert a new one. This means if you do get a collision in your primary key field, it’ll silently overwrite whatever else used to be in the row.

Answered By: Peter DeGlopper

Answer 3

Try this:

The if statement below is to make sure that the model is update able.

Without the if statement you’ll update the id field everytime you resave the model, hence creating a new model everytime

from uuid import uuid4
from django.db import IntegrityError

class Book(models.Model):
    id = models.CharField(primary_key=True, max_length=32)

    def save(self, *args, **kwargs):
        if self.id:
            super(Book, self).save(*args, **kwargs)
            return

        unique = False
        while not unique:
            try:
                self.id = uuid4().hex
                super(Book, self).save(*args, **kwargs)
            except IntegrityError:
                self.id = uuid4().hex
            else:
                unique = True

Answered By: Angky William

Answer 4

The code snippet below uses the secrets library that comes with Python, handles id collisions, and continues to pass integrity errors when there isn’t an id collision.

example of the ids 0TCKybG1qgAhRuEN , yJariA4QN42E9aLf , AZOMrzlkJ-RKh4dp

import secrets
from django.db import models, IntegrityError

class Test(models.Model):
    pk = models.CharField(primary_key=True, max_length=32)

    def save(self, *args, **kwargs):
        unique = False
        while not unique:
            try:
                self.pk = secrets.token_urlsafe(12)
                super(Test, self).save(*args, **kwargs)
            except IntegrityError as e :
                # keep raising the exception if it's not id collision error
                if not 'pk' in e.args[0]:
                    unique = True
                    raise e  
            else:
                unique = True

Answered By: Raad Altaie

Generate a random alphanumeric string as a primary key for a model

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