Django Constraints for PositiveIntegerField in MySQL

Based on the information available, Django does not automatically add check constraints to existing tables during an upgrade. The check constraint for PositiveIntegerField and PositiveSmallIntegerField is only applied when:

1. Creating new tables
2. Explicitly running migrations that add these constraints

Adding Constraints Manually

It is acceptable to add the constraint manually to your MySQL database. You have two options:

Option 1: Create a Django Migration

You can create a migration that adds the constraint using Django's CheckConstraint:

PYTHONCopied
from django.db import migrations, models

class Migration(migrations.Migration):

    dependencies = [
        # Your previous migration
    ]

    operations = [
        migrations.AddConstraint(
            model_name='yourmodel',
            constraint=models.CheckConstraint(
                check=models.Q(your_field__gte=0),
                name='check_your_field_positive',
            ),
        ),
    ]

Option 2: Add Directly in MySQL

You can also add the constraint directly in MySQL using SQL:

SQLCopied
ALTER TABLE your_table_name 
ADD CONSTRAINT check_your_field_positive 
CHECK (your_field_name >= 0);

Considerations

When adding constraints to existing tables:

1. Ensure your existing data doesn't violate the constraint
2. Be aware that adding constraints might lock tables during the operation
3. Test in a staging environment first

Since Django 2.2 introduced the CheckConstraint and UniqueConstraint classes, using these Django features to manage your constraints is generally the recommended approach for better maintainability and compatibility with Django's migration system.