how to add new foreign key in my old django models? - django

Question

I have a model name Employee now i want to add a new fields in this model which will be a foreign key of Department model.I try to solve it the following way but i get error like
django.db.utils.IntegrityError: The row in table 'employee_verification_employee' with primary key 'UP-0319001' has an invalid foreign key: employee_verification_employee.department_id contains a value '03' that does not have a corresponding value in employee_verification_department.id.
class Department(models.Model):
name = models.CharField(max_length=100)
id = models.CharField(primary_key=True,max_length=10)
class Employee(models.Model):
name = models.CharField(max_length=100)
department = models.CharField(max_length=100,choices = Departments)
date_of_joining = models.DateField()
employeed = models.BooleanField(default = True)
email = models.EmailField(max_length = 254)
blood_group = models.CharField(max_length=50)
designation = models.CharField(max_length=100)
image = models.ImageField(upload_to='employee_images',default = "")
number = PhoneField(blank=True, help_text='Enter Contact Number')
emergency_number = PhoneField(blank=True, help_text='Enter Contact Number')
id = models.CharField(primary_key=True, max_length=200)
department_new = models.ForeignKey(Department,on_delete=models.CASCADE,blank=True)
def save(self, *args, **kwargs):
if not self.id:
nth_member = Employee.objects.filter(department = self.department).count()+1
self.id = "UP-" + self.department + self.date_of_joining.strftime("%y")+"{:03d}".format(nth_member)
print(self.id)
super(Employee, self).save(*args, **kwargs)
def __str__(self):
return self.name + "--"+ self.designation``
[![enter image description here][1]][1]
[1]: https://i.stack.imgur.com/xdRMd.png

Answer 1

As #trigo said, all you need is:
class Department(models.Model):
name = models.CharField(max_length=100)
class Employee(models.Model):
name = models.CharField(max_length=100)
department = models.CharField(max_length=100,choices = Departments)
date_of_joining = models.DateField()
employeed = models.BooleanField(default = True)
email = models.EmailField(max_length = 254)
blood_group = models.CharField(max_length=50)
designation = models.CharField(max_length=100)
image = models.ImageField(upload_to='employee_images',default = "")
number = PhoneField(blank=True, help_text='Enter Contact Number')
emergency_number = PhoneField(blank=True, help_text='Enter Contact Number')
department_new = models.ForeignKey(Department,on_delete=models.CASCADE,blank=True)
And Django will take care of the rest (ids).