In Django, your models define the structure of your database. Updating a model means changing its structure, such as:

• Adding/removing fields

• Modifying field types or options

• Changing relationships (ForeignKey, ManyToMany)

• Adding methods or model metadata

Thanks to Django’s migration system, these updates can be applied safely to your database with minimal manual intervention.

This article covers:

• How to update a Django model

• Creating and applying migrations

• Example use cases

• Tips and common pitfalls

When Do You Update a Model?

Here are some common scenarios:

Example Model Before Update

# blog/models.py

from django.db import models

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()
    published = models.BooleanField(default=False)
    created_at = models.DateTimeField(auto_now_add=True)

Step-by-Step: Update the Model

Let’s say we want to:

1. Add a views field

2. Modify the title field's max_length

3. Remove the published field

Step 1: Update the Model Code

# blog/models.py

class Post(models.Model):
    title = models.CharField(max_length=300)  # Updated max_length
    content = models.TextField()
    views = models.IntegerField(default=0)    # New field
    created_at = models.DateTimeField(auto_now_add=True)

Step 2: Make Migrations

Run the following command:

python manage.py makemigrations

This generates a new migration file, e.g.:

Migrations for 'blog':
  blog/migrations/0002_alter_post_title_add_views_remove_published.py

✅ Django detects what changed and generates the required SQL instructions.

Step 3: Apply Migrations

python manage.py migrate

This updates your actual database structure to match your model code.

Example: Changing Field Type

Suppose you want to change the views field from IntegerField to PositiveIntegerField:

# models.py
views = models.PositiveIntegerField(default=0)

Then:

python manage.py makemigrations
python manage.py migrate

Viewing Migration Files

Migrations are Python files stored in each app's migrations/ directory. A migration file might look like this:

# blog/migrations/0002_auto.py

from django.db import migrations, models

class Migration(migrations.Migration):

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

    operations = [
        migrations.AlterField(
            model_name='post',
            name='title',
            field=models.CharField(max_length=300),
        ),
        migrations.RemoveField(
            model_name='post',
            name='published',
        ),
        migrations.AddField(
            model_name='post',
            name='views',
            field=models.IntegerField(default=0),
        ),
    ]

⚙️ Optional: Customizing Migration Behavior

Sometimes you'll need to customize migrations for:

• Default values for new non-null fields (Django prompts you)

• Data transformations during migration (use RunPython)

• Renaming fields without losing data (RenameField)

Best Practices

⚠️ Common Pitfalls

Optional: Rolling Back Migrations

To undo the latest migration:

python manage.py migrate blog 0001

To re-apply:

python manage.py migrate blog

Useful for debugging or correcting mistakes.

Final Example

Original Model:

class Post(models.Model):
    title = models.CharField(max_length=200)
    content = models.TextField()

Updated Model:

class Post(models.Model):
    title = models.CharField(max_length=300)
    content = models.TextField()
    views = models.IntegerField(default=0)

Commands:

python manage.py makemigrations
python manage.py migrate

Conclusion

Updating Django models is a core part of any Django project lifecycle. With Django’s built-in migration system, changing your database schema is safe, trackable, and easy to manage.

As your application grows, understanding how to update models properly will help you maintain a clean and consistent database design.