Find the longest length of a field in a Django model.

max_length.py

from django.db.models import Model, Q
from django.db.models.functions import Length


def max_length(field: str, model: Model) -> int:
    return getattr(
        model.objects.filter(~Q(**{field: None}))
        .annotate(**{f"{field}_length": Length(field)})
        .order_by(f"{field}_length")
        .last(),
        f"{field}_length",
    )