Django - Setting default owner as the logged in user - django

Question

This is a bump post. I have tried various ways and went through all examples here:
https://stackoverflow.com/a/4672123/6274043
https://stackoverflow.com/a/5529770/6274043
How do you specify a default for a Django ForeignKey Model or AdminModel field?
and all doesn't seem to work for me.
# models.py in main/ app
from django.contrib.auth.models import User
class Mileage(models.Model):
owner = models.ForeignKey(User)
date = models.DateField()
... #other parameters
#admin.py
class MileageAdmin(admin.ModelAdmin):
list_display = ['date', ...]
def save_model(self, request, instance, form, change):
user = request.user
instance = form.save(commit=False)
instance.owner= user
instance.save()
form.save_m2m()
return instance
#views.py
def home(request):
form = MileageForm(request.POST or None)
context = {"form": form}
if form.is_valid():
instance = form.save()
form = MileageForm()
context = {"form": form}
return render(request, 'record_trip.html', context)
I am trying to set the default owner as the logged in user. I tried doing it in ModelAdmin like how other posts do but doesn't seem to work. Can any kind soul point out where am I doing it wrong?
It keeps throwing IntegrityError owner_id cannot be null.
Please pardon me if I made elementary mistakes above. I started coding half a year ago for leisure.

Answer 1

Not sure if I understood the question correctly. You are trying to set the logged-in user as the default owner of a newly created model?
Currently, you are only setting created_by and modified_by to default to the logged-in user.
#admin.py
class MileageAdmin(admin.ModelAdmin):
...
def save_model(self, request, instance, form, change):
user = request.user
instance = form.save(commit=False)
if not change or not instance.created_by:
instance.created_by = user
instance.modified_by = user
instance.save()
form.save_m2m()
return instance
But those two fields do not even exist in you example model
class Mileage(models.Model):
owner = models.ForeignKey(User)
date = models.DateField()
... #other parameters
However, you are never actually setting instance.owner to be the request.user. So instance.owner remains to be None, that's why Django complains.
You need to set it before save()ing your instance.
class MileageAdmin(admin.ModelAdmin):
...
def save_model(self, request, instance, form, change):
instance.owner = request.user
if not change or not instance.created_by:
instance.created_by = request.user
instance.modified_by = request.user
instance.save()
form.save_m2m()
return instance

Answer 2

It sounds like the model's save method is getting called somewhere before you've had a chance to set it to the request.user.
You could either find out where that's happening (and perhaps other answers might have a better idea of where that's happening?) or if you wanted a shortcut, you could set the owner attribute to not be a required field, trusting that you'll set it later.
owner = models.ForeignKey(User, blank=True, null=True)
That way, creating the model without the owner wouldn't throw up an integrity error, but you could trust that the owner attribute would eventually be set.