Custom Methods in Model

To calculate or perform tasks, related to a model, you can create custom methods in it. For example, you want to calculate the age of each Person in the database. For this you can create a custom method and write a logic inside the method.

from django.db import models
from datetime import datetime, date

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    full_name = models.CharField(max_length=60, null=True)
    birth_date = models.DateField()
    is_active = models.BooleanField(default=True)

    def __str__(self):
        return f"{self.first_name} {self.last_name}"
    
    def save(self, *args, **kwargs):
        if isinstance(self.birth_date, str):
            self.birth_date = datetime.strptime(self.birth_date, '%Y-%m-%d').date()
        if self.birth_date.year<1960:
            self.is_active=False
        super().save(*args, **kwargs)

    def calculate_age(self):
        today = date.today()
        age = today.year - self.birth_date.year
        return age

The calculate_age() method is added which returns the age of the Person based on the year. You can call the method as follows :

person = Person.objects.get(id=1)
person.calculate_age()

And similarly, this can be used on all Person objects to get the age of a Person.