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.d         


        

Answer 1

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.

Answer 2

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.

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