Django：“NOT NULL 约束失败：users_investment.user_id”错误

Question

I am working on a project where I would like for many users to register for many offered_funds, so I added a ManyToManyField. I also wanted Django to automatically figure out which user was logged in and auto fill the user field so I wrote it in my views.py file. However upon doing so, I came across the error:

NOT NULL constraint failed: users_investment.user_id

Here is my models.py:

# Not sure if this class is relevant to my question
class UserProfile(models.Model):
    user = models.OneToOneField(User)
    first_name = models.CharField(max_length=24)
    last_name = models.CharField(max_length=24)
    phone_number = models.CharField(max_length=12)
    account_type = models.CharField(max_length=55, choices=ACCOUNT_TYPES)

    def __str__(self):
        return self.user.username

class Investment(models.Model):
    user = models.ManyToManyField(User, blank=True)
    offered_fund = models.ForeignKey(OfferedFunds)
    amount = models.IntegerField(default=0)
    purchase_date = models.DateTimeField(auto_now_add=True)

    def __int__(self):
        return self.offered_fund.fund_name.name

my forms.py:

class InvestmentForm(forms.ModelForm):
    class Meta:
        model = Investment
        fields = ('offered_fund','amount')
        exclude = ['user']

and finally, my views.py:

def of_details(request, slug):
    context_dict = {}

    of = get_object_or_404(OfferedFunds, slug=slug)
    context_dict['of'] = of

    default_state = OfferedFunds.objects.get(slug=slug)
    form = InvestmentForm(request.POST or None, initial={'offered_fund': default_state})

    if form.is_valid():
        instance = form.save(commit=False)
        #instance.user = request.user
        instance.offered_fund = default_state
        instance.save()
        instance.user.add(request.user) # Where the problem started
    context_dict['form'] = form

    return render(request, 'funds/offered-funds-details.html', context_dict)

In my views.py I have commented the bit of code that lead to this issue.I cant imagine why Django would be mad that the user field has a value (not null). Anyone have any ideas on how I can solve this? I've don't a python manage.py flush to clear my database already, and still no luck. Thanks

Answer 1

I think your issue is that you are receiving an anonymous user object instead of a fully authenticated user (Django will automatically populate request.user with an anonymous user if an authenticated user isn't logged in. The id for an anonymous user is always None - hence the database constraint fails.

You need to make sure that your user isn't anonymous by checking whether request.user.is_authenticated() first:

if request.user.is_authenticated():
    instance.user.add(request.user)