Developing Restful APIs with Python, Django and Django Rest Framework

Developing Restful APIs with Python, Django and Django Rest Framework

This article is a definitive guide for starters who want to develop projects with RESTful APIs using Python, Django and Django Rest Framework.

This article is a definitive guide for starters who want to develop projects with RESTful APIs using Python, Django and Django Rest Framework.

Introduction
  • Django is a web framework written in Python
  • Python is an interpreted high-level programming language for general-purpose programming
  • API or Application Programming Interface is a set of rules and mechanisms by which one application or component interacts with the others
  • REST or Representational State Transfer is a software architecture

REST APIs

As described in a dissertion by Roy Fielding,

REST is an "architectural style' that basically exploits the existing technology and protocols of the web.
In simple definition, it is the data representation for a client in the format that is suitable for it.

Hence, RESTful + API is a commonly used terminology for the implementation of such architecture and constraints (eg. in web services).

Here is an example GET request from GitHub's API

$ curl https://api.github.com/users/joshuadeguzman

You will see an output similar to this

{
  "login": "joshuadeguzman",
  "id": 20706361,
  "node_id": "MDQ6VXNlcjIwNzA2MzYx",
  "avatar_url": "https://avatars1.githubusercontent.com/u/20706361?v=4",
  "gravatar_id": "",
  "url": "https://api.github.com/users/joshuadeguzman",
  "html_url": "https://github.com/joshuadeguzman",
  "followers_url": "https://api.github.com/users/joshuadeguzman/followers",
  "following_url": "https://api.github.com/users/joshuadeguzman/following{/other_user}",
  "gists_url": "https://api.github.com/users/joshuadeguzman/gists{/gist_id}",
  "starred_url": "https://api.github.com/users/joshuadeguzman/starred{/owner}{/repo}",
  "subscriptions_url": "https://api.github.com/users/joshuadeguzman/subscriptions",
  "organizations_url": "https://api.github.com/users/joshuadeguzman/orgs",
  "repos_url": "https://api.github.com/users/joshuadeguzman/repos",
  "events_url": "https://api.github.com/users/joshuadeguzman/events{/privacy}",
  "received_events_url": "https://api.github.com/users/joshuadeguzman/received_events",
  "type": "User",
  "site_admin": false,
  "name": "Joshua de Guzman",
  "company": "@freelancer",
  "blog": "https://joshuadeguzman.me",
  "location": "Manila, PH",
  "email": null,
  "hireable": true,
  "bio": "Android Engineer at @freelancer. Building tools for humans.",
  "public_repos": 75,
  "public_gists": 2,
  "followers": 38,
  "following": 10,
  "created_at": "2016-07-28T15:19:54Z",
  "updated_at": "2019-06-16T10:26:39Z"
}

Shown above is a data set in JSON format.

JSON or JavaScript Object Notation is an open-standard file format that uses human-readable text to transmit data objects consisting of attribute–value pairs and array data types.
Other formats include XML, INI, CSV, etc. But today, JSON is widely use for its structure is intuitive, making it comfortable to read and map domain objects no matter what programming language is being used.

Python and Django

Python, according to its creator, Guido van Rossum, is a

high-level programming language, and its core design philosophy is all about code readability and a syntax which allows programmers to express concepts in a few lines of code.
Python uses english like words representation (eg. for methods, reserve keywords and control flow) that makes it easier for any beginner to jump right into it. It also features dynamic type system meaning it verifies the type safety of program at runtime. It also does automatic memory management.

print(5 + 5) # This will result to 10

Django is a high-level Python Web Framework that enables developers to deliver projects on time with clean and pragmatic design.

Its flagship features include a design for fast development, a secure and scalable product.

Quick Django Overview

Django's way of propagating changes to your database schema is by means of its migration modules.

Sample User model

from django.db import models

class User(models.Model):
    first_name = models.CharField(max_length=50)
    middle_name = models.CharField(max_length=50)
    last_name = models.CharField(max_length=50)

    def __str__(self):
        return self.name

If any changes are made on your models, run makemigrations

$ python manage.py makemigrations

Finally, you can synchronize the database with the set of models and migrations

$ python manage.py migrate

REST APIs with Django Rest Framework

DRF or Django REST Framework is a powerful and flexible toolkit for building Web APIs. It helps the developers to not reinvent the wheel by rolling out complex and solid REST API from scratch by themselves. Because when your projects become more and more complex, you will soon realise the need of using DRF or other helpful rest framework.

1. Installation & Project Setup

Create project directory

$ mkdir djangoapi

Install virtualenv via pip

A virtual environment enables a project to have additional libraries or changes in packages within its environment without disturbing global or libraries of other environments.

pip is a package management system used to install and manage software packages written in Python.

$ pip install virtualenv

To create an environment folder in your project's directory

$ cd djangoapi
$ virtualenv venv

To activate the environment

$ source venv/bin/activate

To undo these changes to your path, simply run deactivate. More on virtualenv.

Install django, djangorestframework

$ pip install django
$ pip install djangorestframework

Creating a django project

$ django-admin startproject blog

Running your project

$ python manage.py runserver

System check identified no issues (0 silenced).

You have 15 unapplied migration(s). Your project may not work properly until you apply the migrations for app(s): admin, auth, contenttypes, sessions.
Run 'python manage.py migrate' to apply them.

August 16, 2018 - 09:58:36
Django version 2.1, using settings 'blog.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

The unapplied migrations refer to the default migration files included when you start a django project.

To synchronize these migration files, simply run migrate

$ python manage.py migrate

Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying admin.0002_logentry_remove_auto_add... OK
  Applying admin.0003_logentry_add_action_flag_choices... OK
  Applying contenttypes.0002_remove_content_type_name... OK
  Applying auth.0002_alter_permission_name_max_length... OK
  Applying auth.0003_alter_user_email_max_length... OK
  Applying auth.0004_alter_user_username_opts... OK
  Applying auth.0005_alter_user_last_login_null... OK
  Applying auth.0006_require_contenttypes_0002... OK
  Applying auth.0007_alter_validators_add_error_messages... OK
  Applying auth.0008_alter_user_username_max_length... OK
  Applying auth.0009_alter_user_last_name_max_length... OK
  Applying sessions.0001_initial... OK

The default database in our project is currently set to SQLite named db.sqlite3.

Creating a django project's app

$ cd blog
$ python manage.py startapp posts

The project structure should look like

$ find .
./posts
./posts/migrations
./posts/migrations/__init__.py
./posts/models.py
./posts/__init__.py
./posts/apps.py
./posts/admin.py
./posts/tests.py
./posts/views.py
./db.sqlite3
./blog
./blog/__init__.py
./blog/__pycache__
./blog/__pycache__/settings.cpython-36.pyc
./blog/__pycache__/wsgi.cpython-36.pyc
./blog/__pycache__/__init__.cpython-36.pyc
./blog/__pycache__/urls.cpython-36.pyc
./blog/settings.py
./blog/urls.py
./blog/wsgi.py
./manage.py

2. Model

Each model instance is a definitive source of the information about your data. In general, each model pertains to a single table in your database.

# djangoapi/blog/posts/models.py
from django.db import models

# Create your models here.

class Post(models.Model):
    title = models.CharField(max_length=255)
    content = models.TextField()
    is_featured = models.BooleanField(default=False)

    def __str__(self):
        return self.name

__str__ is called by the str() built-in function and by the print statement to compute the "informal" string representation of an object.
If you try running makemigrations, django won't see those changes yet.

$ No changes detected

To solve this, add your posts app to your project's installed apps.

# djangoapi/blog/blog/settings.py

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'posts' # Add it here
]

To continue with the migration of models

$ python manage.py makemigrations

Migrations for 'posts':
  posts/migrations/0001_initial.py
    - Create model Post

$ python manage.py migrate

Operations to perform:
  Apply all migrations: admin, auth, contenttypes, posts, sessions
Running migrations:
  Applying posts.0001_initial... OK


3. Serialization

Serializers allow data structure or object state to be translated into a format that can be stored or transmitted and be reconstructed later on.

Create API's serializers.py and views.py files and isolate them like this

# posts/api
posts/api/serializers.py
posts/api/views.py

# posts/migrations
posts/migrations/

# posts
posts/admin.py
posts/apps.py
posts/models.py
posts/tests.py
posts/views.py
# posts/api/serializers.py

from ..models import Post
from rest_framework import serializers

class PostSerializer(serializers.ModelSerializer):
    class Meta:
        model = Post
        fields = ('title', 'content', 'is_featured') # if not declared, all fields of the model will be shown

In this tutorial we have used ModelSerializer, more on this.

4. Views

A view function, or view for short, is a Python function that takes a Web request and returns a Web response.

# posts/api/views.py

from ..models import Post
from . import serializers
from rest_framework import generics, status
from rest_framework.response import Response

class PostListView(generics.ListAPIView):
    queryset = Post.objects.all()
    serializer_class = serializers.PostSerializer

As seen above, ListAPIView is used for read-only endpoints to represent a collection of model instances.

In this code snippet, we use generics view methods from the rest_framework, more on this.

5. URLs

This is where we setup our routes or URL paths to our designated views in which we expect specific responses for each.

# posts/urls.py

from django.urls import path
from . import views
from .api import views

urlpatterns = [
    path('', views.PostListView.as_view(), name=None)
]

6. Finalizing Setup

Ensure that the rest_framework is added to our project's apps.

# djangoapi/blog/blog/settings.py

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'rest_framework', # Add it here
    'posts'
]

7. Django Admin

Since we haven't setup our POST requests yet, we will be populating the database through django's admin panel.

To do that, create a superuser account admin with password 1234password.

$ python manage.py createsuperuser --email [email protected] --username admin

Password:
Password (again):
This password is too common.
Bypass password validation and create user anyway? [y/N]: y
Superuser created successfully.

Register the model in the admin panel.

# posts/admin.py

from django.contrib import admin
from .models import Post

# Register your models here.
admin.site.register(Post)

That's it. Visit the admin panel and update posts model's records. More on this.

8. Testing our API

$ python manage.py runserver
GET /api/v1/posts/
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

[
    {
        "title": "Example Post #1",
        "content": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
        "is_featured": false
    },
    {
        "title": "Example Post #2",
        "content": "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
        "is_featured": true
    }
]

Great. Now it's time for us to update our views and finish the standard CRUD operations.

9. Adding more views

POST is a method used for creating (sometimes updating) a resource in the database.

# posts/api/views.py

from ..models import Post
from . import serializers
from rest_framework import generics, status
from rest_framework.response import Response

class PostCreateView(generics.CreateAPIView):
    queryset = Post.objects.all()
    serializer_class = serializers.PostSerializer

    def create(self, request, *args, **kwargs):
        super(PostCreateView, self).create(request, args, kwargs)
        response = {"status_code": status.HTTP_200_OK,
                    "message": "Successfully created",
                    "result": request.data}
        return Response(response)

Most often, we separate List and Create view classes when we want to expose a list of data set while easily preventing a certain request to POST or create a resource in the database for that specific List view.

Usecase always varies for apps, you are opt to use ListCreateAPIView or even ViewSets for combining the logic for a set of related views.

Optional: Since we want to display the data in a more systematic way, we override create method and map our inline custom response handler.

Adding more views with methods GET, PATCH, DELETE to handle a specific blog post detail.

class PostDetailView(generics.RetrieveUpdateDestroyAPIView):
    queryset = Post.objects.all()
    serializer_class = serializers.PostSerializer

    def retrieve(self, request, *args, **kwargs):
        super(PostDetailView, self).retrieve(request, args, kwargs)
        instance = self.get_object()
        serializer = self.get_serializer(instance)
        data = serializer.data
        response = {"status_code": status.HTTP_200_OK,
                    "message": "Successfully retrieved",
                    "result": data}
        return Response(response)

    def patch(self, request, *args, **kwargs):
        super(PostDetailView, self).patch(request, args, kwargs)
        instance = self.get_object()
        serializer = self.get_serializer(instance)
        data = serializer.data
        response = {"status_code": status.HTTP_200_OK,
                    "message": "Successfully updated",
                    "result": data}
        return Response(response)

    def delete(self, request, *args, **kwargs):
        super(PostDetailView, self).delete(request, args, kwargs)
        response = {"status_code": status.HTTP_200_OK,
                    "message": "Successfully deleted"}
        return Response(response)

10. Updating URLs

# posts/urls.py

from django.urls import path
from . import views
from .api import views

urlpatterns = [
    path('', views.PostListView.as_view(), name=None),
    path('create/', views.PostCreateView.as_view(), name=None),
    path('<int:pk>/', views.PostDetailView.as_view(), name=None)
]

Now you can send requests to your API via Postman, your app or do a GETrequests from your browser, examples:

POST /api/v1/posts/create/
HTTP 200 OK
Allow: POST, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "status_code": 200,
    "message": "Successfully created",
    "result": {
        "csrfmiddlewaretoken": "rnSUN3XOIghnXA0yKghnQgxg0do39xhorYene5ALw3gWGThK5MjG6YjL8VUb7v2h",
        "title": "Creating a resource",
        "content": "Howdy mate!"
    }
}
GET /api/v1/posts/1/
HTTP 200 OK
Allow: GET, PUT, PATCH, DELETE, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "status_code": 200,
    "message": "Successfully retrieved",
    "result": {
        "title": "Sample Post",
        "content": "Sample Post Content",
        "is_featured": false
    }
}

That's it. You have successfully managed to develop RESTful APIs with DRF! Cheers!

Source code

Available on GitHub.

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Advanced Django Models: Improve Your Python Development

Advanced Django Models: Improve Your Python Development

Master Django models, a core concept of the popular web framework. Dive into advanced topics, like how the Active Record pattern works for Django’s ORM systems

Models are a core concept of the Django framework. According to Django’s design philosophies for models, we should be as explicit as possible with the naming and functionality of our fields, and ensure that we’re including all relevant functionality related to our model in the model itself, rather than in the views or somewhere else. If you’ve worked with Ruby on Rails before, these design philosophies won’t seem new as both Rails and Django implement the Active Record pattern for their object-relational mapping (ORM) systems to handle stored data.

In this post we’ll look at some ways to leverage these philosophies, core Django features, and even some libraries to help make our models better.

getter/setter/deleter properties

As a feature of Python since version 2.2, a property’s usage looks like an attribute but is actually a method. While using a property on a model isn’t that advanced, we can use some underutilized features of the Python property to make our models more powerful.

If you’re using Django’s built-in authentication or have customized your authentication using AbstractBaseUser, you’re probably familiar with the last_login field defined on the User model, which is a saved timestamp of the user’s last login to your application. If we want to use last_login, but also have a field named last_seen saved to a cache more frequently, we could do so pretty easily.

First, we’ll make a Python property that finds a value in the cache, and if it can’t, it returns the value from the database.

accounts/models.py
from django.contrib.auth.base_user import AbstractBaseUser
from django.core.cache import cache


class User(AbstractBaseUser):
    ...
    
    @property
    def last_seen(self):
        """
        Returns the 'last_seen' value from the cache for a User.
        """
        last_seen = cache.get('last_seen_{0}'.format(self.pk))

        # Check cache result, otherwise return the database value
        if last_seen:
            return last_seen

        return self.last_login

Note: I’ve slimmed the model down a bit as there’s a separate tutorial on this blog about specifically customizing the built-in Django user model.

The property above checks our cache for the user’s last_seen value, and if it doesn’t find anything, it will return the user’s stored last_login value from the model. Referencing <instance>.last_seen now provides a much more customizable attribute on our model behind a very simple interface.

We can expand this to include custom behavior when a value is assigned to our property (some_user.last_seen = some_date_time), or when a value is deleted from the property (del some_user.last_seen).

...
    
@last_seen.setter
def last_seen(self, value):
    """
    Sets the 'last_seen_[uuid]' value in the cache for a User.
    """
    now = value

    # Save in the cache
    cache.set('last_seen_{0}'.format(self.pk), now)

@last_seen.deleter
def last_seen(self):
    """
    Removes the 'last_seen' value from the cache.
    """
    # Delete the cache key
    cache.delete('last_seen_{0}'.format(self.pk))
    
...

Now, whenever a value is assigned to our last_seen property, we save it to the cache, and when a value is removed with del, we remove it from the cache. Using setter and deleter is described in the Python documentation but is rarely seen in the wild when looking at Django models.

You may have a use case like this one, where you want to store something that doesn’t necessarily need to be persisted to a traditional database, or for performance reasons, shouldn’t be. Using a custom property like the above example is a great solution.

In a similar use case, the python-social-auth library, a tool for managing user authentication using third-party platforms like GitHub and Twitter, will create and manage updating information in your database based on information from the platform the user logged-in with. In some cases, the information returned won’t match the fields in our database. For example, the python-social-auth library will pass a fullname keyword argument when creating the user. If, perhaps in our database, we used full_name as our attribute name then we might be in a pinch.

A simple way around this is by using the getter/setter pattern from above:

@property
def fullname(self) -> str:
    return self.full_name

@fullname.setter
def fullname(self, value: str):
    self.full_name = value

Now, when python-social-auth saves a user’s fullname to our model (new_user.fullname = 'Some User'), we’ll intercept it and save it to our database field, full_name, instead.

through model relationships

Django’s many-to-many relationships are a great way of handling complex object relationships simply, but they don’t afford us the ability to add custom attributes to the intermediate models they create. By default, this simply includes an identifier and two foreign key references to join the objects together.

Using the Django ManyToManyField through parameter, we can create this intermediate model ourselves and add any additional fields we deem necessary.

If our application, for example, not only needed users to have memberships within groups, but wanted to track when that membership started, we could use a custom intermediate model to do so.

accounts/models.py
import uuid

from django.contrib.auth.base_user import AbstractBaseUser
from django.db import models
from django.utils.timezone import now


class User(AbstractBaseUser):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    …

class Group(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    members = models.ManyToManyField(User, through='Membership')

class Membership(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    joined = models.DateTimeField(editable=False, default=now)

In the example above, we’re still using a ManyToManyField to handle the relationship between a user and a group, but by passing the Membership model using the through keyword argument, we can now add our joined custom attribute to the model to track when the group membership was started. This through model is a standard Django model, it just requires a primary key (we use UUIDs here), and two foreign keys to join the objects together.

Using the same three model pattern, we could create a simple subscription database for our site:

import uuid

from django.contrib.auth.base_user import AbstractBaseUser
from django.db import models
from django.utils.timezone import now


class User(AbstractBaseUser):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    ...

class Plan(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    name = models.CharField(max_length=50, unique=True, default='free')
    subscribers = models.ManyToManyField(User, through='Subscription', related_name='subscriptions', related_query_name='subscriptions')

class Subscription(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    plan = models.ForeignKey(Plan, on_delete=models.CASCADE)
    created = models.DateTimeField(editable=False, default=now)
    updated = models.DateTimeField(auto_now=True)
    cancelled = models.DateTimeField(blank=True, null=True)

Here we’re able to track when a user first subscribed, when they updated their subscription, and if we added the code paths for it, when a user canceled their subscription to our application.

Using through models with the ManyToManyField is a great way to add more data to our intermediate models and provide a more thorough experience for our users without much added work.

Proxy models

Normally in Django, when you subclass a model (this doesn’t include abstract models) into a new class, the framework will create new database tables for that class and link them (via OneToOneField) to the parent database tables. Django calls this “multi-table inheritance” and it’s a great way to re-use existing model fields and structures and add your own data to them. “Don’t repeat yourself,” as the Django design philosophies state.

Multi-table inheritance example:

from django.db import models

class Vehicle(models.Model):
    model = models.CharField(max_length=50)
    manufacturer = models.CharField(max_length=80)
    year = models.IntegerField(max_length=4)

class Airplane(Vehicle):
    is_cargo = models.BooleanField(default=False)
    is_passenger = models.BooleanField(default=True)

This example would create ...

...continue with Proxy Models

Zac Clancy is Vice President at Global DIRT (Disaster Immediate Response Team)