Proxy Model in Django [Explained with Example]

Summary: In this tutorial, you will learn what is proxy model in Django, and how you can use them in your next Django project.

What is Proxy Model in Django?

In Django, a proxy model is a model that inherits from an existing model, but does not have its own database table. Instead, it uses the database table of the model it inherits from.

It is often used to add or change the behavior of the original model, without modifying the original model’s fields or database table.

Consider the following code from models.py for instance:

#models.py

class Car(models.Model):
    name = models.CharField(max_length=30)
    color = models.CharField(max_length=30)

class RedCarManager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(color='red')

class RedCar(Car):
    objects = RedCarManager()
    class Meta:
        proxy = True

In this example, the Car model is the original model, and RedCar is another model that inherits from it.

The RedCar model has a Meta class that has an attribute proxy set to True, indicating that it is a proxy model of Car.

Also, in the example, RedCar model uses a custom manager that overrides the default get_queryset method to filter the cars that have a color of “red”.

This means, when you call RedCar.objects.all() it will only return the cars that are red, instead of returning all the cars in the Car table.

This allows you to easily retrieve only the red cars without having to filter the queryset each time you need it, making your code more readable and efficient.

When to use Proxy Model in Django?

You can use proxy model in various situations, such as:

1. When you want to add or change the behavior of an existing model without modifying the original model’s fields or database table. Like, adding a custom manager or methods to an existing model.
2. When you want to change the default manager of an existing model without modifying the original model.
3. When you want to add additional methods or properties (that do not involve adding new fields to the database) to an existing model.
4. When you want to filter the queryset based on certain conditions on existing model (like in the above example), you can use proxy model.

Example:

Here’s an example of using a proxy model, where we add an additional method to an already existing model:

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)

class PersonFullName(Person):
    class Meta:
        proxy = True

    def full_name(self):
        return f"{self.first_name} {self.last_name}"

In this example, the Person model has two fields first_name and last_name. The PersonFullName is a proxy model of Person, it doesn’t have any new fields, but it has an additional method full_name() which returns the full name of the person by combining the first_name and last_name fields.

You can use this PersonFullName model as you would use the Person model to retrieve records from the database, but now you can also use the full_name() method to get the full name of the person.

person = PersonFullName.objects.get(pk=1)
print(person.full_name())

Summary

To summarize, proxy model in Django is a model that inherits from an existing model but does not have its own database table.

It can be used to add new methods or properties to the existing model, to change default manager, verbose name of model and to filter queryset based on certain conditions, without modifying the original model’s fields or database table.

Also, it is important to be mindful of the trade-offs of using proxy model, always think if a proxy model is the best solution for your specific use case before using it in your code.