getting a django model field from another field - django-models

Question

i have this model
class Person(models.Model):
picture = models.ImageField(
default='default.jpg', upload_to='profile_pics', )
firstName = models.CharField(blank=True, max_length=100)
familyName = models.CharField(blank=True, max_length=100)
age = models.IntegerField(default=0)
GENDER = [
("M", 'Male'),
("F", 'Female'),
("U", 'UNKNOWN'),
]
gender = models.CharField(
max_length=2,
choices=GENDER,
default="U",
)
address = models.CharField(blank=True, max_length=100)
remark = models.TextField(default="no remark")
description_vector = models.TextField(blank=True)
i want to infer the description_vector from the picture field (with a method called identifie(pictur) that return a string ) whenever i add a new Person or changing a model image (if the image didn't change i dont want to change the description_vector)
i know i can use the save method like here but i dont know how to specify that when the image change the vector change.
i dont know if it changes anything but i use django-rest-framowrk to add and change persons
i know

Answer 1

I am not sure I understand what your specific doubt is, but I think this might be helpful.
def save(self, *args, **kwargs):
if self.id is not None: # check only when update
original_picture = self.objects.get(id=self.id).picture
if original_picture !== self.picture # You must add here your method to evaluate if both images are equal
self.vector = some_method_to_change_vector(self.picture)
return super().save(*args, **kwargs)