SplitArrayField.has_changed() is always True for numeric fields.

[Evgeniy Krysanov]

Code example:

# models.py
class Signal(models.Model):
    order_price = ArrayField(models.FloatField(), default=list)

# admin.py
class SignalForm(forms.ModelForm):
    order_price = SplitArrayField(base_field=forms.FloatField(), size=3, remove_trailing_nulls=True, required=False)

@admin.register(Signal)
class SignalAdmin(admin.ModelAdmin):
    form = SignalForm

    def save_model(self, request, obj, form, change):
        super().save_model(request, obj, form, change)
        print(form.has_changed())  # Always True even if no values was changed

[Mariusz Felisiak]

I was not able to reproduce this issue in basic tests. Maybe it is related remove_trailing_nulls=True, do you have them in a database? e.g. [1.33, 5.33. 8.78, None] Can you check initial data?

[Evgeniy Krysanov]

Replying to felixxm:

I was not able to reproduce this issue in basic tests. Maybe it is related remove_trailing_nulls=True, do you have them in a database? e.g. [1.33, 5.33. 8.78, None] Can you check initial data?

I checked a lot of cases until I isolated the problem - ​https://github.com/django/django/blob/master/django/forms/forms.py#L451

initial_value is the original object's value, for example [3.5, 1.0, 2.2]. data_value is converted from form data to ['3.5', '1.0', '2.2'], but not converted to FloatField values. If the initial_value is [] then the data_value is ['', '', '']. Thats why has_changed always returns True.

I fixed this bug in my project with the following code:

class BetterSplitArrayField(SplitArrayField):
    def to_python(self, value):
        return self.clean(value)

When calling field.has_changed(initial_value, data_value)there is a call to data = self.to_python(data) ​https://github.com/django/django/blob/master/django/forms/fields.py#L181 but SplitArrayField just returns the original value from this method. My code fix this.

But it would be better to see the fix in Django source. I can write a PR with unitests if you wish.

[Mariusz Felisiak]

Thanks for details. I was able to reproduce this issue.

[Mariusz Felisiak]

Test.

[Chason Chaffin]

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In c238e65e:

Fixed #30596 -- Fixed SplitArrayField.has_changed() for non-string base fields.

Thanks to Evgeniy Krysanov for the report and the idea to use to_python.
Thanks to Mariusz Felisiak for the test case.