[FIXED] why update is not working when customising the save() in the model class?

Issue

class Person(models.Model):
    SHIRT_SIZES = [
        ("S", "Small"),
        ("M", "Medium"),
        ("L", "Large"),
    ]

    first_name =  models.CharField("person's first name:", max_length = 30, help_text = "User First name")
    last_name  =  models.CharField("Person's Last Name:",max_length = 30, help_text = "User Last name")
    shirt_size =  models.CharField(max_length=1, choices=SHIRT_SIZES, default = "S", help_text = "User shirt size")

    def __str__(self) -> str:
        return self.first_name + ' ' + self.last_name
    
    
    def full_name(self):
        return '%s  %s' %(self.first_name, self.last_name)

    def get_absolute_url(self):
        return "/people/%i/" % self.id;

    def save(self, *args, **kwargs):
    
        self.first_name = "%s %s" %('Mr', self.first_name)
        
        return super().save(self, *args, **kwargs)

Creating a new record is working fine but it's generating an error when updating the existing record.

IntegrityError at /admin/members/person/14/change/
UNIQUE constraint failed: members_person.id
Request Method: POST
Request URL:    http://127.0.0.1:8000/admin/members/person/14/change/
Django Version: 3.2.23
Exception Type: IntegrityError
Exception Value:    
UNIQUE constraint failed: members_person.id
Exception Location: C:\wamp\www\python\myproject\lib\site-packages\django\db\backends\sqlite3\base.py, line 423, in execute
Python Executable:  C:\wamp\www\python\myproject\Scripts\python.exe
Python Version: 3.6.6
Python Path:    
['C:\\wamp\\www\\python\\vleproject',
 'C:\\wamp\\www\\python\\myproject\\Scripts\\python36.zip',
 'C:\\Program Files (x86)\\Microsoft Visual Studio\\Shared\\Python36_64\\DLLs',
 'C:\\Program Files (x86)\\Microsoft Visual Studio\\Shared\\Python36_64\\lib',
 'C:\\Program Files (x86)\\Microsoft Visual Studio\\Shared\\Python36_64',
 'C:\\wamp\\www\\python\\myproject',
 'C:\\wamp\\www\\python\\myproject\\lib\\site-packages']
Server time:    Fri, 12 Jan 2024 13:11:09 +0000

Solution

You should not include self in the super() call:

def save(self, *args, **kwargs):
    self.first_name = "%s %s" %('Mr', self.first_name)
    return super().save(*args, **kwargs)

But this is not a good idea anyway: it will each time add an extra Mr in front.

Answered By - gladiator