Django Model Field Reference ForeignKey
Example
ForeignKey field is used to create a many-to-one relationship between models.
Not like the most of other fields requires positional arguments.
The following example demonstrates the car and owner relation:
from django.db import models
class Person(models.Model):
GENDER_FEMALE = 'F'
GENDER_MALE = 'M'
GENDER_CHOICES = (
(GENDER_FEMALE, 'Female'),
(GENDER_MALE, 'Male'),
)
first_name = models.CharField(max_length=100)
last_name = models.CharField(max_length=100)
gender = models.CharField(max_length=1, choices=GENDER_CHOICES)
age = models.SmallIntegerField()
class Car(model.Model)
owner = models.ForeignKey('Person')
plate = models.CharField(max_length=15)
brand = models.CharField(max_length=50)
model = models.CharField(max_length=50)
color = models.CharField(max_length=50)
The first argument of the field is the class to which the model is related.
The second positional argument is on_delete argument.
In the current versions this argument is not required, but it will be required in Django 2.0.
The default functionality of the argument is shown as following:
class Car(model.Model)
owner = models.ForeignKey('Person', on_delete=models.CASCADE)
...
This will cause Car objects to be deleted from the model when its owner deleted from Person model. This is the default functionality.
class Car(model.Model)
owner = models.ForeignKey('Person', on_delete=models.PROTECT)
...
This will prevents Person objects to be deleted if they are related to at least one Car object. All of the Car objects which reference a Person object should be deleted first. And then the Person Object can be deleted.
