Django 3 Web Development Cookbook: Actionable solutions to common problems in Python web development , Fourth Edition

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Models and Database Structure

In this chapter, we will cover the following topics:

Using model mixins
Creating a model mixin with URL-related methods
Creating a model mixin to handle creation and modification dates
Creating a model mixin to take care of meta tags
Creating a model mixin to handle generic relations
Handling multilingual fields
Working with model translation tables
Avoiding circular dependencies
Adding database constraints
Using migrations
Changing a foreign key to the many-to-many field

Using model mixins

In object-oriented languages, such as Python, a mixin class can be viewed as an interface with implemented features. When a model extends a mixin, it implements the interface and includes all of its fields, attributes, properties, and methods. The mixins in Django models can be used when you want to reuse the generic functionalities in different models multiple times. The model mixins in Django are abstract base model classes. We will explore them in the next few recipes.

Getting ready

First, you will need to create reusable mixins. A good place to keep your model mixins is in a myproject.apps.core app. If you create a reusable app that you will share with others, keep the model mixins in the reusable app itself, possibly in a base.py file.

How to do it...

Open the models.py file of any Django app that you want to use mixins with, and type the following code:

# myproject/apps/ideas/models.py
from django.db import models
from django.urls import reverse
from django.utils.translation import gettext_lazy as _

from myproject.apps.core.models import (
    CreationModificationDateBase,
    MetaTagsBase,
    UrlBase,
)

class Idea(CreationModificationDateBase, MetaTagsBase, UrlBase):
    title = models.CharField(
        _("Title"),
        max_length=200,
    )
    content = models.TextField(
        _("Content"),
    )
    # other fields…

    class Meta:
        verbose_name = _("Idea")
        verbose_name_plural = _("Ideas")

    def __str__(self):
        return self.title

    def get_url_path(self):
        return reverse("idea_details", kwargs={
            "idea_id": str(self.pk),
        })

How it works...

Django's model inheritance supports three types of inheritance: abstract base classes, multi-table inheritance, and proxy models. Model mixins are abstract model classes, in that we define them by using an abstract Meta class, with specified fields, properties, and methods. When you create a model such as Idea, as shown in the preceding example, it inherits all of the features from CreationModificationDateMixin, MetaTagsMixin, and UrlMixin. All of the fields of these abstract classes are saved in the same database table as the fields of the extending model. In the following recipes, you will learn how to define your model mixins.

There's more...

In normal Python class inheritance, if there is more than one base class, and all of them implement a specific method, and you call that method on the instance of a child class, only the method from the first parent class will be called, as in the following example:

>>> class A(object):
... def test(self):
...     print("A.test() called")
... 

>>> class B(object):
... def test(self):
...     print("B.test() called")
... 

>>> class C(object):
... def test(self):
...     print("C.test() called")
... 

>>> class D(A, B, C):
... def test(self):
...     super().test()
...     print("D.test() called")

>>> d = D()
>>> d.test()
A.test() called
D.test() called

This is the same for Django model base classes; however, there is one special exception.

The Django framework does some magic with metaclasses that calls the save() and delete() methods from each of the base classes.

That means that you can confidently do pre-save, post-save, pre-delete, and post-delete manipulations for specific fields defined specifically in the mixin by overwriting the save() and delete() methods.

To learn more about the different types of model inheritance, refer to the official Django documentation, available at https://docs.djangoproject.com/en/2.2/topics/db/models/#model-inheritance.

Django is a web framework for perfectionists with deadlines, designed to help you build manageable medium and large web projects in a short time span. This fourth edition of the Django Web Development Cookbook is updated with Django 3's latest features to guide you effectively through the development process. This Django book starts by helping you create a virtual environment and project structure for building Python web apps. You'll learn how to build models, views, forms, and templates for your web apps and then integrate JavaScript in your Django apps to add more features. As you advance, you'll create responsive multilingual websites, ready to be shared on social networks. The book will take you through uploading and processing images, rendering data in HTML5, PDF, and Excel, using and creating APIs, and navigating different data types in Django. You'll become well-versed in security best practices and caching techniques to enhance your website's security and speed. This edition not only helps you work with the PostgreSQL database but also the MySQL database. You'll also discover advanced recipes for using Django with Docker and Ansible in development, staging, and production environments. By the end of this book, you will have become proficient in using Django's powerful features and will be equipped to create robust websites.

What you will learn

Discover how to set the basic configurations to start any Django project

Understand full-stack web application development using Django

Build a database structure using reusable model mixins

Implement security, performance, and deployment features in your web apps

Import data from local sources and external web services and export it to your app

Secure web applications against malicious usage and find and fix common performance bottlenecks

What do you get with Print?

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Paperback book shipped to your preferred address

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James Jul 01, 2020

Great book if you are currently learning about Django. Can highly recommend, helped me with my studies.

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William H Scholtz Nov 20, 2020

I decided to move my skill level from Ruby/Rails, PHP Zend world to Python/Django world. (Python has become such a popular language)In the process, I worked through multiple books, most of them targeted at the absolute beginner. I bought this by "accident", one my best accidents in a long time. This book gives you recipes for each and all any developer will need to build powerful applications, as well as deploy and manage the deployment servers. The recipes are excellent and to the point. Over the past 25 years as a developer, this is probably the most comprehensive manual I have ever encountered. Not for the beginner, for sure, but all Django developers will eventually need a book like this. Thanks to the authors. It is a "steal" on Kindle for $15. I was getting frustrated with most other books/manuals available. This book solved that problem...

Alex Sep 17, 2020

This is more than what I was expecting! If you're an experienced web developer and you just need a kickstart with Django development - this is it. Just check "Table on content" - you'll get a very good idea of what's inside.Big thank you to the authors! Great work

Martin May 05, 2020

The book gave me a pretty good current (April 2020) Overview of Django and Django Rest Framework. As both technologies are still under heavy development finding print books is not easy. It should still be read with a Django Documentation looked up every now and then.

ChiTownTimmay Jun 04, 2020

If you’re looking for a more detailed explanation of Django concepts, this book builds up your understanding more completely. My path with Django started with the initial Django documentation, and, while good, just was a lot to handle. Then I came across this book and more fully/completely was able to make those connections to concepts better. While I definitely wouldn’t start with this book or use it as a primer, if you’re looking to upskill or increase your understanding of Django, it’s definitely worth a spot on your bookshelf.

Django 3 Web Development Cookbook: Actionable solutions to common problems in Python web development , Fourth Edition

What do you get with Print?

Django 3 Web Development Cookbook

Models and Database Structure

Introduction

Technical requirements

Using model mixins

Getting ready

How to do it...

How it works...

There's more...

See also

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