Convert a BooleanField to a CharField while mainting state in Django

Step 1: Create a temporary field
Step 2: Copy the existing state into the temporary field
Step 3: Alter the original field
Step 4: Cleanup, remove the temporary field

I recently ran into a situation where I needed to convert a BooleanField (True / False) to a CharField with three choices—Yes, No, and Maybe. Django’s migration system makes schema changes straightforward, however, this feature has been in use for a while, and I wanted to preserve both the original state and the field name during the migration.

For this example I’ll use a model called Invite. It’s a simple model that represents an invitation where the recipient RSVPs to attending. Initially the RSVP was a boolean—Yes or No—and we’re adding a third option, Maybe, so we’ll migrate the field to a CharField with choices.

For invitations where a recipient has RSVP’d Yes, we need to preserve that they’re attending, while ensuring new invitations default to Maybe. We also want the option to roll the change back if needed.

We’ll do this in a few steps: create a temporary field, copy the existing values into it, alter the original field to a CharField with the new choices, and then lastly remove the temporary field.

This is the code that we'll be starting with:

invite/models.py

from django.db import models


class Invite(models.Model):
    email = models.EmailField()
    sent_at = models.DateTimeField(auto_now_add=True)
    rsvp_status = models.BooleanField(default=False) # Field to be updated

    def __str__(self) -> str:
        return f"{self.email} - {self.rsvp_status}"

This is what we want the result to be:

invite/models.py

from django.db import models


class RSVPChoices(models.TextChoices):
    YES = "yes", "Yes"
    NO = "no", "No"
    MAYBE = "maybe", "Maybe"


class Invite(models.Model):
    email = models.EmailField()
    sent_at = models.DateTimeField(auto_now_add=True)
    rsvp_status = models.CharField(
        max_length=6, choices=RSVPChoices, default=RSVPChoices.MAYBE
    )

    def __str__(self) -> str:
        return f"{self.email} - {self.rsvp_status}"

Step 1: Create a temporary field

We'll start by defining the available choices for the RSVP status using Django's models.TextChoices subclass. You can read more about them in the Django docs

invite/models.py

class RSVPChoices(models.TextChoices):
    YES = "yes", "Yes"
    NO = "no", "No"
    MAYBE = "maybe", "Maybe"

Now that we’ve defined our choices, we’ll add a temporary field to stage the updated RSVP status. This temporary field should mirror the final field (same max_length and choices) so we can swap it out later (this will make sense soon). For now, we’ll also make it nullable and allow blank values. That avoids any NOT NULL or default value errors Django might raise during this migration. After backfilling the existing rows, we will enforce a default value.

Let's call this field temp_rsvp_status and update the code:

invite/models.py

from django.db import models


class RSVPChoices(models.TextChoices):
    YES = "yes", "Yes"
    NO = "no", "No"
    MAYBE = "maybe", "Maybe"


class Invite(models.Model):
    email = models.EmailField()
    sent_at = models.DateTimeField(auto_now_add=True)
    rsvp_status = models.BooleanField(default=False)
    temp_rsvp_status = models.CharField(
        max_length=6, choices=RSVPChoices, null=True, blank=True
    )

    def __str__(self) -> str:
        return f"{self.email} - {self.rsvp_status}"

Create a migration to have our change take effect.

python manage.py makemigrations

The migration should look something like this:

invite/migrations/0001_initial.py

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('invite', '0001_initial'),
    ]

    operations = [
        migrations.AddField(
            model_name='invite',
            name='temp_rsvp_status',
            field=models.CharField(
                blank=True, 
                choices=[
                    ('yes', 'Yes'), 
                    ('no', 'No'), 
                    ('maybe', 'Maybe')
                ], 
                max_length=6, 
                null=True
            ),
        ),
    ]

Go ahead and apply the migration and have a look at the model in the Django admin. You should see the new field with a dropdown containing all the choices we specified.

Note: Don’t save changes in the admin yet. This is a temporary field that we’ll backfill and swap with the original field in the next steps, and editing it now could result in inconsistent data.

python manage.py migrate

Step 2: Copy the existing state into the temporary field

This is where it starts to get a bit more tricky.

Now that we have the temporary field, we can update it to match the state of the existing rsvp_status field. We want Yes to be selected if the existing rsvp_status is ticked (True) and Maybe if it is not (False).

To do this we need to create an empty migration where we will handle that logic ourselves. For that we'll use the following command:

python manage.py makemigrations <app_name> --empty --name <name_for_the_migration>

The <app_name> is the name of the app that this model lives in. Read more on Django apps in the docs

The <name_for_the_migration> is just a descriptive name for the migration file.

The full command in our case:

python manage.py makemigrations invite --empty --name copy_rsvp_status_details_to_temp

Check your migrations folder in the specified app. We should have an empty migration that looks something like this: