Django unique_together 日期验证约束

Question

I have following model:

class Completion(models.Model):
    date_completed = models.DateTimeField(auto_now=False, auto_now_add=False)
    related_task = models.ForeignKey(Task, on_delete=models.CASCADE)

I need to check that each Completion have unique date (not datetime - only the date) for each Task (which is Completion 's related field). In other words, I need something like this:

class Meta:
    unique_together = [
        'date_completed__date',
        'related_task'
    ]

I know it does not work this way (and should not), so I would like to ask, how can I achieve the desired result (if it is possible altogether).

Answer 1

One way would be to add a new attribute to hold just a DateField and use it for the constraint. I recognize that doesn't do exactly what you ask, and would require allowing nulls first, converting current datetime values for the date only field but depending where you are with this process it may be feasible. As I understand, the uniqueness is enforced at the database level and a function to strip off the time probably isn't going to work.

In the unique_together section

the appropriate UNIQUE statements are included in the CREATE TABLE statement

As a side note, the documentation suggests using UniqueConstraint as

Use UniqueConstraint with the constraints option instead.

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