Django & PostgreSQL CRUD example | Django Rest Framework

In this tutorial, we’re gonna create Python/Django CRUD with PostgreSQL example that uses Django Rest Framework for building Rest Apis. You’ll know:

• How to setup Django to connect with PostgreSQL Database
• How to define Data Models and migrate it to PostgreSQL
• Way to use Django Rest Framework to process HTTP requests
• Way to make Django CRUD Operations with PostgreSQL Database

Related Posts:
– Django & MongoDB CRUD Rest API | Django Rest Framework
– Django CRUD with MySQL example | Django Rest Framework

Fullstack:
– Django + Angular
– Django + React
– Django + React Hooks
– Django + Vue.js

Django CRUD with PostgreSQL overview

We will build Rest Apis using Django Rest Framework that can create, retrieve, update, delete and find Tutorials by title or published status.

First, we setup Django Project with a PostgreSQL Client. Next, we create Rest Api app, add it with Django Rest Framework to the project. Next, we define data model and migrate it to the database. Then we write API Views and define Routes for handling all CRUD operations (including custom finder).
The following table shows overview of the Rest APIs that will be exported:

Finally, we’re gonna test the Rest Apis using Postman.

Architecture

The following diagram shows the architecture of our Django CRUD Rest Apis App with PostgreSQL database:

• HTTP requests will be matched by Url Patterns and passed to the Views
• Views processes the HTTP requests and returns HTTP responses (with the help of Serializer)
• Serializer serializes/deserializes data model objects
• Models contains essential fields and behaviors for CRUD Operations with PostgreSQL Database

Technology

• Python 3.7
• Django 2.1.15
• Django Rest Framework 3.11.0
• psycopg2 2.8.5
• django-cors-headers 3.2.1

Project structure

This is our project directory tree:

• tutorials/apps.py: declares TutorialsConfig class (subclass of django.apps.AppConfig) that represents Rest CRUD Apis app and its configuration.
• DjangoRestApisPostgreSQL/settings.py: contains settings for our Django project: PostgreSQL Database engine, INSTALLED_APPS list with Django REST framework, Tutorials Application, CORS and MIDDLEWARE.
• tutorials/models.py: defines Tutorial data model class (subclass of django.db.models.Model).
• migrations/0001_initial.py: is created when we make migrations for the data model, and will be used for generating PostgreSQL database table.
• tutorials/serializers.py: manages serialization and deserialization with TutorialSerializer class (subclass of rest_framework.serializers.ModelSerializer).
• tutorials/views.py: contains functions to process HTTP requests and produce HTTP responses (using TutorialSerializer).
• tutorials/urls.py: defines URL patterns along with request functions in the Views.
• DjangoRestApisPostgreSQL/urls.py: also has URL patterns that includes tutorials.urls, it is the root URL configurations.

Install Django REST framework

Django REST framework helps us to build RESTful Web Services flexibly.

To install this package, run command:
pip install djangorestframework

Setup new Django project

Let’s create a new Django project with command:

django-admin startproject DjangoRestApisPostgreSQL

When the process is done, you can see folder tree like this:

Now we open settings.py and add Django REST framework to the INSTALLED_APPS array here.

INSTALLED_APPS = [
    ...
    # Django REST framework 
    'rest_framework',
]

Connect Django project to PostgreSQL

We need a Python PostgreSQL adapter to work with PostgreSQL database.
In this tutorial, we use psycopg2.

Run this command to install it: pip install psycopg2.

We also need to setup PostgreSQL Database engine.
So open settings.py and change declaration of DATABASES:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'testdb',
        'USER': 'postgres',
        'PASSWORD': '123',
        'HOST': '127.0.0.1',
        'PORT': '5432',
    }
}

Setup new Django app for Rest CRUD Api

Run following commands to create new Django app tutorials:

cd DjangoRestApisPostgreSQL
python manage.py startapp tutorials

Refresh the project directory tree, then it will look like:

Now open tutorials/apps.py, you can see TutorialsConfig class (subclass of django.apps.AppConfig).
This represents the Django app that we’ve just created with its configuration:

from django.apps import AppConfig


class TutorialsConfig(AppConfig):
    name = 'tutorials'

Don’t forget to add this app to INSTALLED_APPS array in settings.py:

INSTALLED_APPS = [
    ...
    # Tutorials application 
    'tutorials.apps.TutorialsConfig',
]

Configure CORS

We need to allow requests to our Django application from other origins.
In this example, we’re gonna configure CORS to accept requests from localhost:8081.

First, install the django-cors-headers library:
pip install django-cors-headers

In settings.py, add configuration for CORS:

INSTALLED_APPS = [
    ...
    # CORS
    'corsheaders',
]

You also need to add a middleware class to listen in on responses:

MIDDLEWARE = [
    ...
    # CORS
    'corsheaders.middleware.CorsMiddleware',
    'django.middleware.common.CommonMiddleware',
]

Note: CorsMiddleware should be placed as high as possible, especially before any middleware that can generate responses such as CommonMiddleware.

Next, set CORS_ORIGIN_ALLOW_ALL and add the host to CORS_ORIGIN_WHITELIST:

CORS_ORIGIN_ALLOW_ALL = False
CORS_ORIGIN_WHITELIST = (
    'http://localhost:8081',
)

• CORS_ORIGIN_ALLOW_ALL: If True, all origins will be accepted (not use the whitelist below). Defaults to False.
• CORS_ORIGIN_WHITELIST: List of origins that are authorized to make cross-site HTTP requests. Defaults to [].

Define the Django Model

Open tutorials/models.py, add Tutorial class as subclass of django.db.models.Model.
There are 3 fields: title, description, published.

from django.db import models


class Tutorial(models.Model):
    title = models.CharField(max_length=70, blank=False, default='')
    description = models.CharField(max_length=200,blank=False, default='')
    published = models.BooleanField(default=False)

Each field is specified as a class attribute, and each attribute maps to a database column.
id field is added automatically.

Migrate Data Model to PostgreSQL database

Run the Python script: python manage.py makemigrations tutorials.

The console will show:

Migrations for 'tutorials':
  tutorials\migrations\0001_initial.py
    - Create model Tutorial

Refresh the workspace, you can see new file tutorials/migrations/0001_initial.py.
It includes code to create Tutorial data model:

# Generated by Django 2.1.15

from django.db import migrations, models


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Tutorial',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('title', models.CharField(default='', max_length=70)),
                ('description', models.CharField(default='', max_length=200)),
                ('published', models.BooleanField(default=False)),
            ],
        ),
    ]

The generated code defines Migration class (subclass of the django.db.migrations.Migration).
It has operations array that contains operation for creating Customer model table: migrations.CreateModel().

The call to this will create a new model in the project history and a corresponding table in the database to match it.

To apply the generated migration above, run the following Python script:
python manage.py migrate tutorials

The console will show:

Operations to perform:
  Apply all migrations: tutorials
Running migrations:
  Applying tutorials.0001_initial... OK

At this time, you can see that a table for Tutorial model was generated automatically in PostgreSQL database with the name: tutorials_tutorial:

Create Serializer class for Data Model

Let’s create TutorialSerializer class that will manage serialization and deserialization from JSON.

It inherit from rest_framework.serializers.ModelSerializer superclass which automatically populates a set of fields and default validators. We need to specify the model class here.

tutorials/serializers.py

from rest_framework import serializers 
from tutorials.models import Tutorial
 
 
class TutorialSerializer(serializers.ModelSerializer):
 
    class Meta:
        model = Tutorial
        fields = ('id',
                  'title',
                  'description',
                  'published')

In the inner class Meta, we declare 2 attributes:

• model: the model for Serializer
• fields: a tuple of field names to be included in the serialization

Define Routes to Views functions

When a client sends request for an endpoint using HTTP request (GET, POST, PUT, DELETE), we need to determine how the server will response by defining the routes.

These are our routes:

• /api/tutorials: GET, POST, DELETE
• /api/tutorials/:id: GET, PUT, DELETE
• /api/tutorials/published: GET

Create a urls.py inside tutorials app with urlpatterns containing urls to be matched with request functions in the views.py:

from django.conf.urls import url 
from tutorials import views 
 
urlpatterns = [ 
    url(r'^api/tutorials$', views.tutorial_list),
    url(r'^api/tutorials/(?P<pk>[0-9]+)$', views.tutorial_detail),
    url(r'^api/tutorials/published$', views.tutorial_list_published)
]

Don’t forget to include this URL patterns in root URL configurations.
Open DjangoRestApisPostgreSQL/urls.py and modify the content with the following code:

from django.conf.urls import url, include 
 
urlpatterns = [ 
    url(r'^', include('tutorials.urls')),
]

Write API Views

We’re gonna create these API functions for CRUD Operations:
– tutorial_list(): GET list of tutorials, POST a new tutorial, DELETE all tutorials
– tutorial_detail(): GET / PUT / DELETE tutorial by ‘id’
– tutorial_list_published(): GET all published tutorials

Open tutorials/views.py and write following code:

from django.shortcuts import render

from django.http.response import JsonResponse
from rest_framework.parsers import JSONParser 
from rest_framework import status
 
from tutorials.models import Tutorial
from tutorials.serializers import TutorialSerializer
from rest_framework.decorators import api_view


@api_view(['GET', 'POST', 'DELETE'])
def tutorial_list(request):
    # GET list of tutorials, POST a new tutorial, DELETE all tutorials
 
 
@api_view(['GET', 'PUT', 'DELETE'])
def tutorial_detail(request, pk):
    # find tutorial by pk (id)
    try: 
        tutorial = Tutorial.objects.get(pk=pk) 
    except Tutorial.DoesNotExist: 
        return JsonResponse({'message': 'The tutorial does not exist'}, status=status.HTTP_404_NOT_FOUND) 
 
    # GET / PUT / DELETE tutorial
    
        
@api_view(['GET'])
def tutorial_list_published(request):
    # GET all published tutorials

Let’s implement these functions.

Create a new object

Create and Save a new Tutorial:

@api_view(['GET', 'POST', 'DELETE'])
def tutorial_list(request):
    ...
 
    elif request.method == 'POST':
        tutorial_data = JSONParser().parse(request)
        tutorial_serializer = TutorialSerializer(data=tutorial_data)
        if tutorial_serializer.is_valid():
            tutorial_serializer.save()
            return JsonResponse(tutorial_serializer.data, status=status.HTTP_201_CREATED) 
        return JsonResponse(tutorial_serializer.errors, status=status.HTTP_400_BAD_REQUEST)

Retrieve objects (with condition)

Retrieve all Tutorials/ find by title from PostgreSQL database:

@api_view(['GET', 'POST', 'DELETE'])
def tutorial_list(request):
    if request.method == 'GET':
        tutorials = Tutorial.objects.all()
        
        title = request.GET.get('title', None)
        if title is not None:
            tutorials = tutorials.filter(title__icontains=title)
        
        tutorials_serializer = TutorialSerializer(tutorials, many=True)
        return JsonResponse(tutorials_serializer.data, safe=False)
        # 'safe=False' for objects serialization

Retrieve a single object

Find a single Tutorial with an id:

@api_view(['GET', 'PUT', 'DELETE'])
def tutorial_detail(request, pk):
    # ... tutorial = Tutorial.objects.get(pk=pk)
 
    if request.method == 'GET': 
        tutorial_serializer = TutorialSerializer(tutorial) 
        return JsonResponse(tutorial_serializer.data) 

Update an object

Update a Tutorial by the id in the request:

@api_view(['GET', 'PUT', 'DELETE'])
def tutorial_detail(request, pk):
    # ... tutorial = Tutorial.objects.get(pk=pk)
    # ...
 
    elif request.method == 'PUT': 
        tutorial_data = JSONParser().parse(request) 
        tutorial_serializer = TutorialSerializer(tutorial, data=tutorial_data) 
        if tutorial_serializer.is_valid(): 
            tutorial_serializer.save() 
            return JsonResponse(tutorial_serializer.data) 
        return JsonResponse(tutorial_serializer.errors, status=status.HTTP_400_BAD_REQUEST) 

Delete an object

Delete a Tutorial with the specified id:

@api_view(['GET', 'PUT', 'DELETE'])
def tutorial_detail(request, pk):
    # ... tutorial = Tutorial.objects.get(pk=pk)
    # ...
 
    elif request.method == 'DELETE': 
        tutorial.delete() 
        return JsonResponse({'message': 'Tutorial was deleted successfully!'}, status=status.HTTP_204_NO_CONTENT)

Delete all objects

Delete all Tutorials from the database:

@api_view(['GET', 'POST', 'DELETE'])
def tutorial_list(request):
    # ...
    
    elif request.method == 'DELETE':
        count = Tutorial.objects.all().delete()
        return JsonResponse({'message': '{} Tutorials were deleted successfully!'.format(count[0])}, status=status.HTTP_204_NO_CONTENT)

Find all objects by condition

Find all Tutorials with published = True:

@api_view(['GET'])
def tutorial_list_published(request):
    tutorials = Tutorial.objects.filter(published=True)
        
    if request.method == 'GET': 
        tutorials_serializer = TutorialSerializer(tutorials, many=True)
        return JsonResponse(tutorials_serializer.data, safe=False)

Test the CRUD with APIs

Run our Django Project with command: python manage.py runserver 8080.
The console shows:

Performing system checks...

System check identified no issues (0 silenced).

Run 'python manage.py migrate' to apply them.
May 08, 2020 - 10:02:34
Django version 2.1.15, using settings 'DjangoRestApisPostgreSQL.settings'
Starting development server at http://127.0.0.1:8080/
Quit the server with CTRL-BREAK.

Using Postman, we’re gonna test all the Apis above.

1. Create a new Tutorial using POST /tutorials Api




Check tutorials_tutorial table after creating some objects:



2. Retrieve all Tutorials using GET /tutorials Api




3. Retrieve a single Tutorial by id using GET /tutorials/:id Api




4. Update a Tutorial using PUT /tutorials/:id Api




Check the table after some rows were updated:



5. Find all Tutorials which title contains ‘pos’: GET /tutorials?title=pos




6. Find all published Tutorials using GET /tutorials/published Api




7. Delete a Tutorial using DELETE /tutorials/:id Api




Tutorial with id=4 was removed from PostgreSQL table:



8. Delete all Tutorials using DELETE /tutorials Api

You can use the Simple HTTP Client using Axios to check it.

Or: Simple HTTP Client using Fetch API

Conclusion

Today, we’ve learned how to create Django CRUD PostgreSQL example Django Rest Framework for Rest Apis. We also know way to connect Django application with PostgreSQL database, create a Django Model, migrate it to database, write the Views and define Url patterns for handling all CRUD operations.

Happy learning! See you again.

Further Reading

• Django Rest Framework quich start
• Django Model
• https://github.com/psycopg/psycopg2
• https://github.com/adamchainz/django-cors-headers

Fullstack CRUD App:

• Django + React
• Django + React Hooks
• Django + Vue
• Django + Angular

Source code

You can find the complete source code for this example on Github.