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# Tutorial 1: Serialization
## Introduction
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This tutorial will cover creating a simple pastebin code highlighting Web API. Along the way it will introduce the various components that make up REST framework, and give you a comprehensive understanding of how everything fits together.
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The tutorial is fairly in-depth, so you should probably get a cookie and a cup of your favorite brew before getting started. If you just want a quick overview, you should head over to the [quickstart] documentation instead.
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!!! note
The code for this tutorial is available in the [encode/rest-framework-tutorial][repo] repository on GitHub. Feel free to clone the repository and see the code in action.
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## Setting up a new environment
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Before we do anything else we'll create a new virtual environment called `.venv` , using [venv]. This will make sure our package configuration is kept nicely isolated from any other projects we're working on.
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=== ":fontawesome-brands-linux: Linux, :fontawesome-brands-apple: macOS"
```bash
python3 -m venv .venv
source .venv/bin/activate
` ``
=== ":fontawesome-brands-windows: Windows"
If you use Bash for Windows
` ``bash
python3 -m venv .venv
source .venv\Scripts\activate
` ``
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Now that we're inside a virtual environment, we can install our package requirements.
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` ``bash
pip install django
pip install djangorestframework
pip install pygments # We'll be using this for the code highlighting
` ``
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!!! tip
To exit the virtual environment at any time, just type ` deactivate`. For more information see the [venv documentation][venv].
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## Getting started
Okay, we're ready to get coding.
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To get started, let's create a new project to work with.
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` ``bash
cd ~
django-admin startproject tutorial
cd tutorial
` ``
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Once that's done we can create an app that we'll use to create a simple Web API.
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` ``bash
python manage.py startapp snippets
` ``
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We'll need to add our new ` snippets` app and the ` rest_framework` app to ` INSTALLED_APPS`. Let's edit the ` tutorial/settings.py` file:
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` ``text
INSTALLED_APPS = [
...
'rest_framework',
'snippets',
]
` ``
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Okay, we're ready to roll.
## Creating a model to work with
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For the purposes of this tutorial we're going to start by creating a simple ` Snippet` model that is used to store code snippets. Go ahead and edit the ` snippets/models.py` file. Note: Good programming practices include comments. Although you will find them in our repository version of this tutorial code, we have omitted them here to focus on the code itself.
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` ``python
from django.db import models
from pygments.lexers import get_all_lexers
from pygments.styles import get_all_styles
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LEXERS = [item for item in get_all_lexers() if item[1]]
LANGUAGE_CHOICES = sorted([(item[1][0], item[0]) for item in LEXERS])
STYLE_CHOICES = sorted([(item, item) for item in get_all_styles()])
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class Snippet(models.Model):
created = models.DateTimeField(auto_now_add=True)
title = models.CharField(max_length=100, blank=True, default="")
code = models.TextField()
linenos = models.BooleanField(default=False)
language = models.CharField(
choices=LANGUAGE_CHOICES, default="python", max_length=100
)
style = models.CharField(choices=STYLE_CHOICES, default="friendly", max_length=100)
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class Meta:
ordering = ["created"]
` ``
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We'll also need to create an initial migration for our snippet model, and sync the database for the first time.
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` ``bash
python manage.py makemigrations snippets
python manage.py migrate snippets
` ``
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## Creating a Serializer class
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The first thing we need to get started on our Web API is to provide a way of serializing and deserializing the snippet instances into representations such as ` json`. We can do this by declaring serializers that work very similar to Django's forms. Create a file in the ` snippets` directory named ` serializers.py` and add the following.
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` ``python
from rest_framework import serializers
from snippets.models import Snippet, LANGUAGE_CHOICES, STYLE_CHOICES
class SnippetSerializer(serializers.Serializer):
id = serializers.IntegerField(read_only=True)
title = serializers.CharField(required=False, allow_blank=True, max_length=100)
code = serializers.CharField(style={"base_template": "textarea.html"})
linenos = serializers.BooleanField(required=False)
language = serializers.ChoiceField(choices=LANGUAGE_CHOICES, default="python")
style = serializers.ChoiceField(choices=STYLE_CHOICES, default="friendly")
def create(self, validated_data):
"""
Create and return a new ` Snippet` instance, given the validated data.
"""
return Snippet.objects.create(**validated_data)
def update(self, instance, validated_data):
"""
Update and return an existing ` Snippet` instance, given the validated data.
"""
instance.title = validated_data.get("title", instance.title)
instance.code = validated_data.get("code", instance.code)
instance.linenos = validated_data.get("linenos", instance.linenos)
instance.language = validated_data.get("language", instance.language)
instance.style = validated_data.get("style", instance.style)
instance.save()
return instance
` ``
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The first part of the serializer class defines the fields that get serialized/deserialized. The ` create()` and ` update()` methods define how fully fledged instances are created or modified when calling ` serializer.save()`
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A serializer class is very similar to a Django ` Form` class, and includes similar validation flags on the various fields, such as ` required`, ` max_length` and ` default`.
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The field flags can also control how the serializer should be displayed in certain circumstances, such as when rendering to HTML. The ` {'base_template': 'textarea.html'}` flag above is equivalent to using ` widget=widgets.Textarea` on a Django ` Form` class. This is particularly useful for controlling how the browsable API should be displayed, as we'll see later in the tutorial.
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We can actually also save ourselves some time by using the ` ModelSerializer` class, as we'll see later, but for now we'll keep our serializer definition explicit.
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## Working with Serializers
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Before we go any further we'll familiarize ourselves with using our new Serializer class. Let's drop into the Django shell.
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` ``bash
python manage.py shell
` ``
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Okay, once we've got a few imports out of the way, let's create a couple of code snippets to work with.
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` ``pycon
>>> from snippets.models import Snippet
>>> from snippets.serializers import SnippetSerializer
>>> from rest_framework.renderers import JSONRenderer
>>> from rest_framework.parsers import JSONParser
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>>> snippet = Snippet(code='foo = "bar"\n')
>>> snippet.save()
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>>> snippet = Snippet(code='print("hello, world")\n')
>>> snippet.save()
` ``
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We've now got a few snippet instances to play with. Let's take a look at serializing one of those instances.
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` ``pycon
>>> serializer = SnippetSerializer(snippet)
>>> serializer.data
{'id': 2, 'title': '', 'code': 'print("hello, world")\n', 'linenos': False, 'language': 'python', 'style': 'friendly'}
` ``
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At this point we've translated the model instance into Python native datatypes. To finalize the serialization process we render the data into ` json`.
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` ``pycon
>>> content = JSONRenderer().render(serializer.data)
>>> content
b'{"id":2,"title":"","code":"print(\\"hello, world\\")\\n","linenos":false,"language":"python","style":"friendly"}'
` ``
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Deserialization is similar. First we parse a stream into Python native datatypes...
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` ``pycon
>>> import io
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>>> stream = io.BytesIO(content)
>>> data = JSONParser().parse(stream)
` ``
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...then we restore those native datatypes into a fully populated object instance.
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` ``pycon
>>> serializer = SnippetSerializer(data=data)
>>> serializer.is_valid()
True
>>> serializer.validated_data
{'title': '', 'code': 'print("hello, world")', 'linenos': False, 'language': 'python', 'style': 'friendly'}
>>> serializer.save()
<Snippet: Snippet object>
` ``
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Notice how similar the API is to working with forms. The similarity should become even more apparent when we start writing views that use our serializer.
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We can also serialize querysets instead of model instances. To do so we simply add a ` many=True` flag to the serializer arguments.
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` ``pycon
>>> serializer = SnippetSerializer(Snippet.objects.all(), many=True)
>>> serializer.data
[{'id': 1, 'title': '', 'code': 'foo = "bar"\n', 'linenos': False, 'language': 'python', 'style': 'friendly'}, {'id': 2, 'title': '', 'code': 'print("hello, world")\n', 'linenos': False, 'language': 'python', 'style': 'friendly'}, {'id': 3, 'title': '', 'code': 'print("hello, world")', 'linenos': False, 'language': 'python', 'style': 'friendly'}]
` ``
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## Using ModelSerializers
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Our ` SnippetSerializer` class is replicating a lot of information that's also contained in the ` Snippet` model. It would be nice if we could keep our code a bit more concise.
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In the same way that Django provides both ` Form` classes and ` ModelForm` classes, REST framework includes both ` Serializer` classes, and ` ModelSerializer` classes.
Let's look at refactoring our serializer using the ` ModelSerializer` class.
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Open the file ` snippets/serializers.py` again, and replace the ` SnippetSerializer` class with the following.
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` ``python
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from rest_framework import serializers
from snippets.models import Snippet
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class SnippetSerializer(serializers.ModelSerializer):
class Meta:
model = Snippet
fields = ["id", "title", "code", "linenos", "language", "style"]
` ``
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One nice property that serializers have is that you can inspect all the fields in a serializer instance, by printing its representation. Open the Django shell with ` python manage.py shell`, then try the following:
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` ``pycon
>>> from snippets.serializers import SnippetSerializer
>>> serializer = SnippetSerializer()
>>> print(repr(serializer))
SnippetSerializer():
id = IntegerField(label='ID', read_only=True)
title = CharField(allow_blank=True, max_length=100, required=False)
code = CharField(style={'base_template': 'textarea.html'})
linenos = BooleanField(required=False)
language = ChoiceField(choices=[('Clipper', 'FoxPro'), ('Cucumber', 'Gherkin'), ('RobotFramework', 'RobotFramework'), ('abap', 'ABAP'), ('ada', 'Ada')...
style = ChoiceField(choices=[('autumn', 'autumn'), ('borland', 'borland'), ('bw', 'bw'), ('colorful', 'colorful')...
` ``
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It's important to remember that ` ModelSerializer` classes don't do anything particularly magical, they are simply a shortcut for creating serializer classes:
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* An automatically determined set of fields.
* Simple default implementations for the ` create()` and ` update()` methods.
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## Writing regular Django views using our Serializer
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Let's see how we can write some API views using our new Serializer class.
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For the moment we won't use any of REST framework's other features, we'll just write the views as regular Django views.
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Edit the ` snippets/views.py` file, and add the following.
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` ``python
from django.http import HttpResponse, JsonResponse
from django.views.decorators.csrf import csrf_exempt
from rest_framework.parsers import JSONParser
from snippets.models import Snippet
from snippets.serializers import SnippetSerializer
` ``
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The root of our API is going to be a view that supports listing all the existing snippets, or creating a new snippet.
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` ``python
@csrf_exempt
def snippet_list(request):
"""
List all code snippets, or create a new snippet.
"""
if request.method == "GET":
snippets = Snippet.objects.all()
serializer = SnippetSerializer(snippets, many=True)
return JsonResponse(serializer.data, safe=False)
elif request.method == "POST":
data = JSONParser().parse(request)
serializer = SnippetSerializer(data=data)
if serializer.is_valid():
serializer.save()
return JsonResponse(serializer.data, status=201)
return JsonResponse(serializer.errors, status=400)
` ``
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Note that because we want to be able to POST to this view from clients that won't have a CSRF token we need to mark the view as ` csrf_exempt`. This isn't something that you'd normally want to do, and REST framework views actually use more sensible behavior than this, but it'll do for our purposes right now.
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We'll also need a view which corresponds to an individual snippet, and can be used to retrieve, update or delete the snippet.
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` ``python
@csrf_exempt
def snippet_detail(request, pk):
"""
Retrieve, update or delete a code snippet.
"""
try:
snippet = Snippet.objects.get(pk=pk)
except Snippet.DoesNotExist:
return HttpResponse(status=404)
if request.method == "GET":
serializer = SnippetSerializer(snippet)
return JsonResponse(serializer.data)
elif request.method == "PUT":
data = JSONParser().parse(request)
serializer = SnippetSerializer(snippet, data=data)
if serializer.is_valid():
serializer.save()
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return JsonResponse(serializer.data)
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return JsonResponse(serializer.errors, status=400)
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elif request.method == "DELETE":
snippet.delete()
return HttpResponse(status=204)
` ``
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Finally we need to wire these views up. Create the ` snippets/urls.py` file:
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` ``python
from django.urls import path
from snippets import views
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urlpatterns = [
path("snippets/", views.snippet_list),
path("snippets/<int:pk>/", views.snippet_detail),
]
` ``
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We also need to wire up the root urlconf, in the ` tutorial/urls.py` file, to include our snippet app's URLs.
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` ``python
from django.urls import path, include
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urlpatterns = [
path("", include("snippets.urls")),
]
` ``
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It's worth noting that there are a couple of edge cases we're not dealing with properly at the moment. If we send malformed ` json`, or if a request is made with a method that the view doesn't handle, then we'll end up with a 500 "server error" response. Still, this'll do for now.
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## Testing our first attempt at a Web API
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Now we can start up a sample server that serves our snippets.
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Quit out of the shell...
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` ``pycon
>>> quit()
` ``
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...and start up Django's development server.
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` ``bash
python manage.py runserver
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Validating models...
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0 errors found
Django version 5.0, using settings 'tutorial.settings'
Starting Development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.
` ``
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In another terminal window, we can test the server.
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We can test our API using [curl][curl] or [HTTPie][HTTPie]. HTTPie is a user-friendly http client that's written in Python. Let's install that.
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You can install HTTPie using pip:
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` ``bash
pip install httpie
` ``
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Finally, we can get a list of all of the snippets:
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` ``bash
http GET http://127.0.0.1:8000/snippets/ --unsorted
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HTTP/1.1 200 OK
...
[
{
"id": 1,
"title": "",
"code": "foo = \"bar\"\n",
"linenos": false,
"language": "python",
"style": "friendly"
},
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{
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"id": 2,
"title": "",
"code": "print(\"hello, world\")\n",
"linenos": false,
"language": "python",
"style": "friendly"
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},
{
"id": 3,
"title": "",
"code": "print(\"hello, world\")",
"linenos": false,
"language": "python",
"style": "friendly"
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}
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]
` ``
Or we can get a particular snippet by referencing its id:
` ``bash
http GET http://127.0.0.1:8000/snippets/2/ --unsorted
HTTP/1.1 200 OK
...
{
"id": 2,
"title": "",
"code": "print(\"hello, world\")\n",
"linenos": false,
"language": "python",
"style": "friendly"
}
` ``
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Similarly, you can have the same json displayed by visiting these URLs in a web browser.
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## Where are we now
We're doing okay so far, we've got a serialization API that feels pretty similar to Django's Forms API, and some regular Django views.
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Our API views don't do anything particularly special at the moment, beyond serving ` json` responses, and there are some error handling edge cases we'd still like to clean up, but it's a functioning Web API.
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We'll see how we can start to improve things in [part 2 of the tutorial][tut-2].
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[quickstart]: quickstart.md
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[repo]: https://github.com/encode/rest-framework-tutorial
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[venv]: https://docs.python.org/3/library/venv.html
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[tut-2]: 2-requests-and-responses.md
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[HTTPie]: https://github.com/httpie/httpie#installation
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[curl]: https://curl.haxx.se/
