Django CreateView- ModelForm with many-to-many InlineFormset ValueError - django

Question

I'm struggling with such a problem:
I have models:
class ForecastType(models.Model):
client = models.ForeignKey(Client, related_name="weatherforecast_client")
created_by = models.ForeignKey(Forecaster, related_name="weatherforecast_created_by")
modified_by = models.ForeignKey(Forecaster,
related_name="weatherforecast_modified_by",
blank=True,
null=True)
creation_date = models.DateTimeField(auto_now_add=True)
modification_date = models.DateTimeField(auto_now=True)
weather_forecasts = models.ManyToManyField('WeatherForecast')
STATUS_CHOICES = (
("D", "Draft"),
("A", "Active"),
("H", "History"),
)
status = models.CharField(max_length=1, choices=STATUS_CHOICES, default="D")
class OneDayForecast(ForecastType):
def __str__(self):
return f"Prognoza pogody dla: {self.client}, wykonana dnia: {self.creation_date}"
class WeatherForecast(models.Model):
begin_date = models.DateTimeField(blank=True, null=True)
finish_date = models.DateTimeField(blank=True, null=True)
forecast_type = models.ForeignKey('ForecastType', null=True, blank=True)
description = models.TextField(max_length=300, blank=True, null=True)
I also have ModelForm and InlineFormset:
class OneDayForecastForm(ModelForm):
class Meta:
model = OneDayForecast
exclude = ('weather_forecasts',)
WeatherForecastFormset = inlineformset_factory(OneDayForecast, WeatherForecast, exclude=('forecast_type',), extra=2)
and finally an CreateView:
class OneDayForecast(ForecasterRequiredMixin, CreateView):
template_name = "forecaster/one_day.html"
success_url = reverse_lazy("forecaster:dashboard")
model = OneDayForecast
form_class = OneDayForecastForm
def get(self, request, *args, **kwargs):
self.object = None
form_class = self.get_form_class()
form = self.get_form(form_class)
weather_forecast_form = WeatherForecastFormset()
return self.render_to_response(
self.get_context_data(form=form, weather_forecast_form=weather_forecast_form)
)
def post(self, request, *args, **kwargs):
self.object = None
form_class = self.get_form_class()
form = self.get_form(form_class)
weather_forecast_form = WeatherForecastFormset(self.request.POST)
if form.is_valid() and weather_forecast_form.is_valid():
return self.form_valid(form, weather_forecast_form)
else:
return self.form_invalid(form, weather_forecast_form)
def form_valid(self, form, weather_forecast_form):
self.object = form.save(commit=False)
for weather_form in weather_forecast_form:
weather_object = weather_form.save()
self.object.weatherforecast_set.add(weather_object)
self.object.save()
form.save_m2m()
return HttpResponseRedirect(self.get_success_url())
def form_invalid(self, form, weather_forecast_form):
return self.render_to_response(
self.get_context_data(form=form, weather_forecast_form=weather_forecast_form)
)
After trying to submit my Form with it's InlineFormset I receive this error:
Request Method: POST
Request URL: http://localhost:8000/forecaster/my-clients/6/one_day/
Django Version: 1.11
Exception Type: ValueError
Exception Value:
Unsaved model instance <OneDayForecast: Forecast for: client1> cannot be used in an ORM query.
Problem probably lies in commit=False in form_valid method but I have no clue how to repair it.
Does anyone know to solve this?
Thanks.

Answer 1

Okay, so I think that there are a couple problems here, both in your post and form_valid() methods. I've referred to my own implementations of inline formsets to see what you do differently.
First of all, I believe that the first line of the post method should be self.object = self.get_object().
Second, weather_forecast_form = WeatherForecastFormset(self.request.POST) should be weather_forecast_form = WeatherForecastFormset(self.request.POST, instance=self.object).
Notice the relationship here between the object we get and then using it at the instance in the formset. That's all for the post method.
Now, in my own implementation, I have many formsets, so I loop through each formset as follows (you can use exactly the same code if you put your formset into a list and pass it to form_valid):
def form_valid(self, form, formsets):
self.object = form.save()
for formset in formsets:
formset.instance = self.object
formset.save()
return HttpResponseRedirect(self.get_success_url())
Notice that we fully save the parent form here, including committing it. We then save all formsets. If you wanted to keep your single formset, you can easily change the above code to the following:
def form_valid(self, form, weather_forecast_form):
self.object = form.save()
weather_forecast_form.instance = self.object
weather_forecast_form.save()
return HttpResponseRedirect(self.get_success_url())
The error that you report at the bottom of your question is a direct result of form.save(commit=False). What is happening there is that you are "pretend" saving the parent, and then trying to fully save the children. The database doesn't have record of the parent, so it spits out that error. Committing before saving many to many records is a must (at least in my experience).