Django exists query not work in if and else clause? - mysql

Question

In given below if Medicine table consists medicine_name then query execute fine, but when medicine name doesn't exist on the Corresponding table then error is occured.
Matching Query Doesn't Exists
views.py Code
#api_view(['POST'])
def addPeople(request):
m = People()
m.bp_no = request.POST['bp_no']
m.name = request.POST['name']
m.corporation_name = request.POST['corporation_name']
m.medicine_name = request.POST['medicine_name']
m.no_of_medicine = request.POST['no_of_medicine']
existing = Medicine.objects.get(medicine_name=m.medicine_name).no_of_medicine - int(m.no_of_medicine)
p_key = Medicine.objects.get(medicine_name=m.medicine_name).id
if Medicine.objects.filter(medicine_name=m.medicine_name).exists():
if existing > 0:
m.save()
Medicine.objects.filter(id=p_key).update(no_of_medicine=existing)
return Response({"message": "Successfully Recorded"})
else:
return Response({"message": "Not much Medicine Stored"})
else:
return Response({"message": "Medicine is not Stored"})
models.py
class People(models.Model):
bp_no = models.IntegerField(blank=False,null=False)
name = models.CharField(blank=False,null=False,max_length=200)
corporation_name = models.CharField(blank=False,null=False,max_length=200)
medicine_name = models.CharField(blank=False,null=False,max_length=200)
no_of_medicine = models.IntegerField()
class Medicine(models.Model):
medicine_name = models.CharField(null=False,blank=False,max_length=200)
no_of_medicine = models.IntegerField(null=False,blank=False)
def __str__(self):
return self.medicine_name
Error Traceback: When Medicine table doesn't contains the corresponding filter name then This error will be shown
Internal Server Error: /api/add-people/
Traceback (most recent call last):
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\core\handlers\exception.py", line 47, in inner
response = get_response(request)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\core\handlers\base.py", line 181, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\views\decorators\csrf.py", line 54, in wrapped_view
return view_func(*args, **kwargs)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\views\generic\base.py", line 70, in view
return self.dispatch(request, *args, **kwargs)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\rest_framework\views.py", line 509, in dispatch
response = self.handle_exception(exc)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\rest_framework\views.py", line 469, in handle_exception
self.raise_uncaught_exception(exc)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\rest_framework\views.py", line 480, in raise_uncaught_exception
raise exc
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\rest_framework\views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\rest_framework\decorators.py", line 50, in handler
return func(*args, **kwargs)
File "E:\django\backend\medirecords\api\views.py", line 37, in addPeople
existing = Medicine.objects.get(medicine_name=m.medicine_name).no_of_medicine - int(m.no_of_medicine)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\db\models\manager.py", line 85, in manager_method
return getattr(self.get_queryset(), name)(*args, **kwargs)
File "C:\Users\MonirHossain\AppData\Roaming\Python\Python39\site-packages\django\db\models\query.py", line 435, in get
raise self.model.DoesNotExist(
api.models.Medicine.DoesNotExist: Medicine matching query does not exist.

Answer 1

I haven't tested this, but purely in terms of handling objects not found, I have a suggestion you can try to simplify the conditions / flow.
.get(): Wrap in try / except
get(*args, **kwargs) raises Model.DoesNotExist when not found.
When there's a not found, you need to determine how you want to handle it. For example, you can have a default fallback value, or raise an error.
In this case the code would fail if the existing medicine wasn't found, so I will have it raise.
#api_view(["POST"])
def addPeople(request):
medicine_name = request.POST["medicine_name"]
try:
medicine = Medicine.objects.get(medicine_name=medicine_name)
except Medicine.DoesNotExist:
return Response({"message": "Not much Medicine Stored"})
m = People()
m.bp_no = request.POST["bp_no"]
m.name = request.POST["name"]
m.corporation_name = request.POST["corporation_name"]
m.medicine_name = medicine_name
m.no_of_medicine = request.POST["no_of_medicine"]
existing = medicine.no_of_medicine - int(m.no_of_medicine)
p_key = medicine.id
if medicine.exists():
if existing > 0:
m.save()
medicine.num_of_medicine = existing
medicine.save(update_fields=["num_of_medicine"])
return Response({"message": "Successfully Recorded"})
else:
return Response({"message": "Not much Medicine Stored"})
else:
return Response({"message": "Medicine is not Stored"})
Move object check earlier
Since the request relies on Medicine, this is should be caught early as possible.
Uses try/catch as .get() will always raise when object is not found
The alternative is to do .exists() or filter(*args, **kwargs) + .first()
Update dependent model via Model.save() and limit field updated to num_of_medicine via update_fields.
get_object_or_404()
get_object_or_404(klass, *args, **kwargs) can also be used in lieu of the earlier try/catch block:
from django.shortcuts import get_object_or_404
medicine = get_object_or_404(Medicine.objects.all(), medicine_name=m.medicine_name)
existing = medicine.no_of_medicine - int(m.no_of_medicine)
Final note
I'm assuming this is an example, but it also may be good to validate request.POST["no_of_medicine"] in the POST data against a backend source of truth to make sure it's not faked.