Buggy Migrations when `float("nan")` in `Q` objects

[Steven Jin]

When creating a CheckConstraint in the form

class MyModel(Model):
  x = FloatField()
  class Meta:
    constraints = [~CheckConstraint(check=Q(x=float("nan")), name="some constraint")]

This constraint is removed and added back every time python manage.py makemigrations is run. This is because the inherited __eq__ function of Q objects does not take into account the fact that float("nan") != float("nan").

See PR: ​https://github.com/django/django/pull/14706

[Mariusz Felisiak]

Thanks for the report, however it looks like a hypothetical issue, what do you want to check with such constraint? (float('nan') != whatever). FloatField uses a proper data type and this should be ensured on a database layer without extra constraints. I don't think it's worth additional complexity.

[Steven Jin]

Thanks for the reply! How would I ensure that values in a column are not nan?

[Simon Charette]

Have you tried to simply compare against the NaN string?

~CheckConstraint(check=Q(x='NaN'), name="not_nan")

It seems to work for me on PostgreSQL.

[Steven Jin]

Thanks!

Replying to Simon Charette:

Have you tried to simply compare against the NaN string?

~CheckConstraint(check=Q(x='NaN'), name="not_nan")

It seems to work for me on PostgreSQL.