django：外键约束失败

Question

In my django project when I'm trying to add a faculty it throws a "FOREIGN KEY constraint failed" error. Here I'm trying to save the faculty under the institute and all the roles have a user login which is linked with a one to one field models.py:

class CustomUser(AbstractBaseUser):
    is_admin = models.BooleanField(default=False)
    is_institute = models.BooleanField(default=False)
    is_faculty = models.BooleanField(default=False)
    is_student = models.BooleanField(default=False)
    user_email = models.EmailField(verbose_name='Email',primary_key=True,unique=True)
    date_created = models.DateTimeField(verbose_name='date created', auto_now_add=True)
    last_login = models.DateTimeField(verbose_name='last login', auto_now=True)
    is_active = models.BooleanField(default=True)
    is_superuser = models.BooleanField(default=False)
    user_image = models.ImageField(upload_to='profile_images',null=True,blank=True)


    USERNAME_FIELD = 'user_email'

class Institute(models.Model):
    user = models.OneToOneField('CustomUser',primary_key=True,on_delete=models.CASCADE)
    institute_name = models.CharField(max_length=75,verbose_name="Institute Name",null=True,blank=True)
    institute_address = models.TextField(max_length=100,verbose_name="Address",null=True,blank=True)
    institute_number = models.PositiveBigIntegerField(verbose_name="Mobile Number",null=True,blank=True)
    institute_id = models.IntegerField(unique=True,verbose_name="Institute Id",null=True,blank=True)

class Faculty(models.Model):
    user = models.OneToOneField('CustomUser',primary_key=True,on_delete=models.CASCADE)
    faculty_id = models.CharField(max_length=75,verbose_name="Faculty Id",null=True,blank=True)
    first_name = models.CharField(max_length=75,verbose_name="First Name",null=True,blank=True)
    last_name = models.CharField(max_length=75,verbose_name="Last Name",null=True,blank=True)
    faculty_number = models.PositiveIntegerField(verbose_name="Mobile Number",null=True,blank=True)
    institute = models.ForeignKey('Institute',on_delete=models.CASCADE)
    class Meta:
        unique_together = [['faculty_id','institute']]

views.py add faculty function:

def addFaculty(request):
    if request.method == "POST":
        user  = CustomUser.objects.create_user(user_email=request.POST.get('user_email'),role="faculty",password=request.POST.get('password'))
        user.save()
        Faculty.objects.create(user=user,faculty_id=request.POST.get('faculty_id'),faculty_number=request.POST.get('faculty_number'),first_name=request.POST.get('first_name'),last_name=request.POST.get('last_name'),institute=Institute(user=request.user)).save()
        return redirect('dashboard')
    else:
        extraFields = [
            {
                'label':"First Name",
                'name':'first_name',
                'type':'text'
            },
            {
                'label':"Last Name",
                'name':'last_name',
                'type':'text'
            },
            {
                'label':"Faculty Id",
                'name':'faculty_id',
                'type':'number'
            },
            {
                'label':"Faculty Number",
                'name':'faculty_number',
                'type':'number'
            }
        ]
        return render(request,'learnerApp/addUser.html',context={'extraFields':extraFields})

Answer 1

You try to specify the institute like so while creating the Faculty instance:

Faculty.objects.create(..., institute=Institute(user=request.user)).save()

This does not work because the instance you provide is not saved to the database it is just created in python. In fact this style of writing code can be said to be somewhat bad as that one line of code is doing multiple things at the same time. You can write it better as:

faculty_id = request.POST.get('faculty_id')
faculty_number = request.POST.get('faculty_number')
first_name = request.POST.get('first_name')
last_name = request.POST.get('last_name')
institute = Institute.objects.create(user=request.user)
Faculty.objects.create(user=user, faculty_id=faculty_id, faculty_number=faculty_number, first_name=first_name, last_name=last_name, institute=institute)

Note: This is still not a very ideal implementation, you are directly using values from request.POST which are not cleaned or validated. You should use a Form [Django docs] or a ModelForm [Django docs] instead.