Re: Eliminating inter-request race conditions

Hi Nick,

I've thought a bit more about this, but it seems that my requirements are different from yours: E.g. I don't need the client-side validation and especially don't want the complexity that goes with it; on the other hand, I need something that also works with formsets, not only with individual forms.

Am 27.12.21 um 06:36 schrieb Nick Farrell:
> *The problems *(from highest to lowest priority)*:*
> [...]
> *2)* Not being able to safely lock a model/queryset beyond the lifetime of the request.

I don't quite understand this. It sounds like pessimistic locking?

> *3)* Not knowing that data has changed on the server until you submit a form.
> *4)* Smarter form validation

Well, this comes at the cost of the complexity to implement this. For me, at least at this time, the cost is much to high to consider this.

> *The solutions*
>
> *Enhanced forms*
> - when rendering a form (using e.g. as_p()), alongside the normal INPUT DOM elements, include additional hidden fields which store a copy of each form field's initial value.

I don't think that having hidden fields with the initial values is necessary: In your view, you can initialize the form like this:

if request.method == 'POST':
form = SomeForm(request.POST, initial=init)
...

Note the `initial` parameter: It is used just as it is in the GET request. This allows you to use `form.changed_data` and `form.has_changed()` in form validation.

Note that the above, i.e. reconstructing the initial values also for POST requests, is useful both for individual forms and even more with multiple forms, i.e. formsets: If for example you edit a list (formset) of appointments, in formset validation you must make sure that the list of appointments has not changed in the meantime (e.g. appointments were not inserted, replaced or deleted).

Best regards,
Carsten

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