Readonly fields with db_default display DatabaseDefault representation

[Mariusz Felisiak]

Readonly fields with db_default display DatabaseDefault() representation in the admin. For example:

• models.py

  class MyModel(models.Model):
      uuid = models.UUIDField(db_default=UUID7(), editable=False, primary_key=True)
      created_datetime = models.DateTimeField(db_default=Now(), editable=False)
      modified_datetime = models.DateTimeField(db_default=Now(), editable=False)
      name = models.TextField()
  

• admin.py

@admin.register(MyModel)
class MyModelAdmin(admin.ModelAdmin):
    readonly_fields = ["uuid", "created_datetime", "modified_datetime"]

I think they should be consider as any other empty values.

[Mariusz Felisiak]

We wanted to add DatabaseDefault() to the list of Field.empty_values and modify its __hash__ and __eq__. Unfortunately, expression is required to initialize DatabaseDefault and, TBH, DatabaseDefaults with different expression should not be consider equal. I'm thinking about adding is_value_empty() hook to the models.Field:

def is_value_empty(self, value):
    return value in self.empty_values or isinstance(value, DatabaseDefault):

and reusing it everywhere we currently check if value in self.empty_values.

[Jacob Walls]

Thanks for the report. The hook does sound better than a misleading __eq__()!

[Mariusz Felisiak]

​PR

[Jacob Walls]

After review, I think adjusting the admin hooks only is safest.

[GitHub <noreply@…>]

In 77d0c9d:

Fixed #37168 -- Made admin display database defaults as empty values.

[Mariusz Felisiak <felisiak.mariusz@…>]

In a5405b87:

[6.1.x] Fixed #37168 -- Made admin display database defaults as empty values.

Backport of 77d0c9d549a8d95156c833eceb6275d9b7317d4e from main