Question

models.py

class KEBReading(models.Model):
    #id = models.AutoField(primary_key=True,db_column='kr_id')
    date=models.DateField()
    time=models.TimeField()
    truepower_reading=models.DecimalField(max_digits=6,
    decimal_places=2,blank=False,null=False)
    apparentpower_reading=models.DecimalField(max_digits=6,
    decimal_places=2,blank=False,null=False)
    truepower_consumed=models.DecimalField(max_digits=6, decimal_places=2)
    voltage_reading=models.IntegerField(blank=False,null=False)
    powerfactor=models.DecimalField(max_digits=3,decimal_places=2)

forms.py

class KEBReading_form(forms.ModelForm):
    class Meta:
        model=KEBReading

        exclude=("truepower_consumed","powerfactor")
        widgets = {

               "date" : forms.widgets.DateInput(format="%d/%m/%Y"),
               "time" : forms.widgets.TimeInput(format="%H:%M")
               }

views.py

def KEBReading1(request):
    if request.method == "POST":


        form = KEBReading_form(request.POST)
        if form.is_valid():
            prevdate=KEBReading.objects.latest("date")

            print prevdate.date
            print prevdate.time
        # q1 = KEBReading.objects.get(datetime.date.today()-datetime.timedelta(0))

            kr_truepower_reading = form.cleaned_data["truepower_reading"]
            kr_apparentpower_reading = form.cleaned_data["apparentpower_reading"]
            truepower_consumed1=kr_truepower_reading-prevdate.truepower_reading
            powerfactor1=kr_truepower_reading-                                           prevdate.truepower_reading/(kr_apparentpower_reading-prevdate.apparentpower_reading)


            form.save()
            KEBReading.objects.filter().values("date","time","truepower_reading",
            "apparentpower_reading","truepower_consumed","voltage","powerfactor")
            q2=KEBReading.objects.latest("date")

            context={'KEBReading_form':form,'q2':q2}
            return                  render_to_response('keb.html',context,context_instance=RequestContext(request))

        else:
            form = KEBReading_form()

            return render_to_response('keb.html',{'KEBReading_form':form},context_instance=RequestContext(request))

i want to save the truepower_consumed aftr calculation in the database. but it gives me a error truepower_consumed column cannot be null. i have excluded truepower_consumed in the forms. but in the database i need to save that field

Answer 1

You need to save form with commit=False and assign appropriate values to required fields and save the object again.

Example:

def KEBReading1(request):
    if request.method == "POST":
    ....
    #your code till save
    obj = form.save(commit=False)
    #assing your values
    obj.truepower_consumed = truepower_consumed1
    obj.powerfactor = powerfactor1
    obj.save() #save

More details at Using a subset of fields on the form