Django's Approach to Uniqueness Constraints

Based on the available documentation, Django has been moving toward using more flexible constraint options in the Meta class, particularly with the introduction of CheckConstraint and UniqueConstraint in Django 2.2.

The documentation specifically recommends using UniqueConstraint with the constraints option instead of unique_together, noting that:

UniqueConstraint provides more functionality than unique_together. unique_together may be deprecated in the future.

However, there isn't an explicit recommendation in the provided documentation about replacing the field-level unique=True option with UniqueConstraint. This appears to be an inconsistency in the migration path.

Possible rationales for this inconsistency:

1. Single-field vs. Multi-field: unique=True is applied to a single field, making it conceptually simpler than unique_together which handles multiple fields. The field-level option might be considered more intuitive for single-field constraints.

2. Historical reasons: The field-level unique=True option has been a core part of Django's model definition since early versions, and changing this pattern might break backward compatibility or developer expectations.

3. Readability considerations: Having uniqueness defined at the field level can make the model more immediately readable, as constraints are visible right where the field is defined.

If you're looking for consistency in your codebase, you could certainly use UniqueConstraint in the Meta.constraints option for all uniqueness requirements, including single-field constraints. This would align with the direction Django seems to be heading with its constraint management.

PYTHONCopied
class MyModel(models.Model):
    name = models.CharField(max_length=100)
    
    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['name'], name='unique_name')
        ]

This approach would be consistent with Django's recommendation for unique_together, though it's worth noting that the field-level unique=True option remains fully supported.