Django throws an integrity error while deleting an user

Question

I have a project in which students can be added, when i try to delete the student who has been added django shows an error like this

IntegrityError at /student/delete/1

FOREIGN KEY constraint failed

Request Method:     GET
Request URL:    http://127.0.0.1:8000/student/delete/1
Django Version:     3.1.1
Exception Type:     IntegrityError
Exception Value:    

FOREIGN KEY constraint failed

Exception Location:     C:\Users\name\AppData\Local\Programs\Python\Python310\lib\site-packages\django\db\backends\base\base.py, line 242, in _commit
Python Executable:  C:\Users\name\AppData\Local\Programs\Python\Python310\python.exe
Python Version:     3.10.2
Python Path:    

['C:\\Users\\name\\Desktop\\test-projects\\college-management-sytem_withstaffsentmailFinal',
 'C:\\Users\\name\\AppData\\Local\\Programs\\Python\\Python310\\python310.zip',
 'C:\\Users\\name\\AppData\\Local\\Programs\\Python\\Python310\\DLLs',
 'C:\\Users\\name\\AppData\\Local\\Programs\\Python\\Python310\\lib',
 'C:\\Users\\name\\AppData\\Local\\Programs\\Python\\Python310',
 'C:\\Users\\name\\AppData\\Local\\Programs\\Python\\Python310\\lib\\site-packages']

Server time:    Mon, 18 Apr 2022 06:35:06 +0100

here is the django model

class Student(models.Model):
    admin = models.OneToOneField(CustomUser, on_delete=models.CASCADE)
    course = models.ForeignKey(Course, on_delete=models.DO_NOTHING, null=True, blank=False)
    session = models.ForeignKey(Session, on_delete=models.DO_NOTHING, null=True)
    
    def __str__(self):
        return self.admin.last_name + ", " + self.admin.first_name


class Staff(models.Model):
    course = models.ForeignKey(Course, on_delete=models.DO_NOTHING, null=True, blank=False)
    admin = models.OneToOneField(CustomUser, on_delete=models.CASCADE)

    def __str__(self):
        return self.admin.last_name + " " + self.admin.first_name

is there any way to fix this error ?