A Django model example
from django.db import models
class Car(models.Model):
brand = models.CharField(max_length=40)
doors = models.IntegerField(default=5)
color = models.CharField(max_length=30)It's important and a good practice to use singular name on your models. Use Car and not Cars, this is because the model represent a single object of the Car and not all the cars in your database. It's also important to notice that the model definition is a class and then we use CamelCase to name them. Examples: Car, CarCompany. The attributes are named with snake_case. Examples: brand, brand_name.
How to structure the model
The coding style from Django suggest that we use this order when we set up the model:
- Choices
- The attributes
- The meta class
- String method
- Custom save method
- Absolute url method
- Other custom methods you need
Here is an example of a Django model with all fields:
from django.db import models
from django.urls import reverse
class Car(models.Model):
SEDAN = 0
COMBI = 1
CABRIOLET = 2
CHOICES_CHASSIS = (
(SEDAN, 'Sedan'),
(COMBI, 'Combi'),
(CABRIOLET, 'Cabriolet')
)
brand = models.CharField('Brand', max_length=40)
chassis = models.IntegerField('Chassis', choices=CHOICES_CHASSIS)
class Meta:
ordering = ('name',)
def __str__(self):
return self.brand
def save(self, *args, **kwargs):
perform_action() # Perform custom action
super().save(*args, **kwargs) # Perform the actual save
def get_absolute_url(self):
return reverse('car_detail', kwargs={'pk': self.id})
def perform_action():
print('This is a action called from the custom save method')Django's ForeignKey
A very cool thing about the ForeignKey(Reverse relationship) is that you can define something called a "related_name". This let's you add a name to the relationship that is actually meaningful.
Here is an example on how to use the ForeignKey:
from django.db import models
class Brand(models.Model):
name = models.CharField('Brand', max_length=40)
class Model(models.Model):
name = models.CharField('Name', max_length=50)
brand = models.ForeignKey(Brand, on_delete=models.CASCADE, related_name='models')
# How to use in a QuerySet
brand = Brand.objects.get(name='BMW')
models = brand.models.all()The blanks and the null
What is the difference between null and blank?
null = this is the database value. If you set null=True the database will accept null as value.
blank = this is django validation on the field. If you set blank=False (this is default) and you use this in a form,
a error will be displayed if the value is empty.
If you want to read more about Django's models I would suggest to get the book Two Scoops of Django. They have written so much good information on the subject.