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<h1 id="tutorial-1-serialization">Tutorial 1: Serialization</h1>
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<h2 id="introduction">Introduction</h2>
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<p>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.</p>
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<p>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 <a href="../quickstart">quickstart</a> documentation instead.</p>
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<hr />
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<p><strong>Note</strong>: The code for this tutorial is available in the <a href="https://github.com/tomchristie/rest-framework-tutorial">tomchristie/rest-framework-tutorial</a> repository on GitHub. The completed implementation is also online as a sandbox version for testing, <a href="http://restframework.herokuapp.com/">available here</a>.</p>
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<hr />
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<h2 id="setting-up-a-new-environment">Setting up a new environment</h2>
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<p>Before we do anything else we'll create a new virtual environment, using <a href="http://www.virtualenv.org/en/latest/index.html">virtualenv</a>. This will make sure our package configuration is kept nicely isolated from any other projects we're working on.</p>
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<pre><code>:::bash
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virtualenv env
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source env/bin/activate
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</code></pre>
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<p>Now that we're inside a virtualenv environment, we can install our package requirements.</p>
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<pre><code>pip install django
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pip install djangorestframework
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pip install pygments # We'll be using this for the code highlighting
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</code></pre>
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<p><strong>Note:</strong> To exit the virtualenv environment at any time, just type <code>deactivate</code>. For more information see the <a href="http://www.virtualenv.org/en/latest/index.html">virtualenv documentation</a>.</p>
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<h2 id="getting-started">Getting started</h2>
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<p>Okay, we're ready to get coding.
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To get started, let's create a new project to work with.</p>
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<pre><code>cd ~
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django-admin.py startproject tutorial
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cd tutorial
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</code></pre>
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<p>Once that's done we can create an app that we'll use to create a simple Web API.</p>
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<pre><code>python manage.py startapp snippets
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</code></pre>
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<p>We'll need to add our new <code>snippets</code> app and the <code>rest_framework</code> app to <code>INSTALLED_APPS</code>. Let's edit the <code>tutorial/settings.py</code> file:</p>
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<pre><code>INSTALLED_APPS = (
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...
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'rest_framework',
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'snippets',
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)
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</code></pre>
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<p>We also need to wire up the root urlconf, in the <code>tutorial/urls.py</code> file, to include our snippet app's URLs.</p>
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<pre><code>urlpatterns = [
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url(r'^', include('snippets.urls')),
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]
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</code></pre>
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<p>Okay, we're ready to roll.</p>
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<h2 id="creating-a-model-to-work-with">Creating a model to work with</h2>
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<p>For the purposes of this tutorial we're going to start by creating a simple <code>Snippet</code> model that is used to store code snippets. Go ahead and edit the <code>snippets/models.py</code> 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.</p>
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<pre><code>from django.db import models
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from pygments.lexers import get_all_lexers
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from pygments.styles import get_all_styles
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LEXERS = [item for item in get_all_lexers() if item[1]]
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LANGUAGE_CHOICES = sorted([(item[1][0], item[0]) for item in LEXERS])
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STYLE_CHOICES = sorted((item, item) for item in get_all_styles())
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class Snippet(models.Model):
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created = models.DateTimeField(auto_now_add=True)
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title = models.CharField(max_length=100, blank=True, default='')
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code = models.TextField()
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linenos = models.BooleanField(default=False)
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language = models.CharField(choices=LANGUAGE_CHOICES,
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default='python',
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max_length=100)
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style = models.CharField(choices=STYLE_CHOICES,
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default='friendly',
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max_length=100)
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class Meta:
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ordering = ('created',)
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</code></pre>
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<p>We'll also need to create an initial migration for our snippet model, and sync the database for the first time.</p>
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<pre><code>python manage.py makemigrations snippets
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python manage.py migrate
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</code></pre>
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<h2 id="creating-a-serializer-class">Creating a Serializer class</h2>
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<p>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 <code>json</code>. We can do this by declaring serializers that work very similar to Django's forms. Create a file in the <code>snippets</code> directory named <code>serializers.py</code> and add the following.</p>
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<pre><code>from django.forms import widgets
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from rest_framework import serializers
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from snippets.models import Snippet, LANGUAGE_CHOICES, STYLE_CHOICES
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class SnippetSerializer(serializers.Serializer):
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pk = serializers.IntegerField(read_only=True)
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title = serializers.CharField(required=False,
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max_length=100)
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code = serializers.CharField(style={'type': 'textarea'})
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linenos = serializers.BooleanField(required=False)
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language = serializers.ChoiceField(choices=LANGUAGE_CHOICES,
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default='python')
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style = serializers.ChoiceField(choices=STYLE_CHOICES,
|
|
default='friendly')
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def create(self, validated_attrs):
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"""
|
|
Create and return a new `Snippet` instance, given the validated data.
|
|
"""
|
|
return Snippet.objects.create(**validated_attrs)
|
|
|
|
def update(self, instance, validated_attrs):
|
|
"""
|
|
Update and return an existing `Snippet` instance, given the validated data.
|
|
"""
|
|
instance.title = validated_attrs.get('title', instance.title)
|
|
instance.code = validated_attrs.get('code', instance.code)
|
|
instance.linenos = validated_attrs.get('linenos', instance.linenos)
|
|
instance.language = validated_attrs.get('language', instance.language)
|
|
instance.style = validated_attrs.get('style', instance.style)
|
|
instance.save()
|
|
return instance
|
|
</code></pre>
|
|
<p>The first part of the serializer class defines the fields that get serialized/deserialized. The <code>create()</code> and <code>update()</code> methods define how fully fledged instances are created or modified when calling <code>serializer.save()</code></p>
|
|
<p>A serializer class is very similar to a Django <code>Form</code> class, and includes similar validation flags on the various fields, such as <code>required</code>, <code>max_length</code> and <code>default</code>.</p>
|
|
<p>The field flags can also control how the serializer should be displayed in certain circumstances, such as when rendering to HTML. The <code>style={'type': 'textarea'}</code> flag above is equivelent to using <code>widget=widgets.Textarea</code> on a Django <code>Form</code> class. This is particularly useful for controlling how the browsable API should be displayed, as we'll see later in the tutorial.</p>
|
|
<p>We can actually also save ourselves some time by using the <code>ModelSerializer</code> class, as we'll see later, but for now we'll keep our serializer definition explicit.</p>
|
|
<h2 id="working-with-serializers">Working with Serializers</h2>
|
|
<p>Before we go any further we'll familiarize ourselves with using our new Serializer class. Let's drop into the Django shell.</p>
|
|
<pre><code>python manage.py shell
|
|
</code></pre>
|
|
<p>Okay, once we've got a few imports out of the way, let's create a couple of code snippets to work with.</p>
|
|
<pre><code>from snippets.models import Snippet
|
|
from snippets.serializers import SnippetSerializer
|
|
from rest_framework.renderers import JSONRenderer
|
|
from rest_framework.parsers import JSONParser
|
|
|
|
snippet = Snippet(code='foo = "bar"\n')
|
|
snippet.save()
|
|
|
|
snippet = Snippet(code='print "hello, world"\n')
|
|
snippet.save()
|
|
</code></pre>
|
|
<p>We've now got a few snippet instances to play with. Let's take a look at serializing one of those instances.</p>
|
|
<pre><code>serializer = SnippetSerializer(snippet)
|
|
serializer.data
|
|
# {'pk': 2, 'title': u'', 'code': u'print "hello, world"\n', 'linenos': False, 'language': u'python', 'style': u'friendly'}
|
|
</code></pre>
|
|
<p>At this point we've translated the model instance into Python native datatypes. To finalize the serialization process we render the data into <code>json</code>.</p>
|
|
<pre><code>content = JSONRenderer().render(serializer.data)
|
|
content
|
|
# '{"pk": 2, "title": "", "code": "print \\"hello, world\\"\\n", "linenos": false, "language": "python", "style": "friendly"}'
|
|
</code></pre>
|
|
<p>Deserialization is similar. First we parse a stream into Python native datatypes...</p>
|
|
<pre><code># This import will use either `StringIO.StringIO` or `io.BytesIO`
|
|
# as appropriate, depending on if we're running Python 2 or Python 3.
|
|
from rest_framework.compat import BytesIO
|
|
|
|
stream = BytesIO(content)
|
|
data = JSONParser().parse(stream)
|
|
</code></pre>
|
|
<p>...then we restore those native datatypes into to a fully populated object instance.</p>
|
|
<pre><code>serializer = SnippetSerializer(data=data)
|
|
serializer.is_valid()
|
|
# True
|
|
serializer.object
|
|
# <Snippet: Snippet object>
|
|
</code></pre>
|
|
<p>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.</p>
|
|
<p>We can also serialize querysets instead of model instances. To do so we simply add a <code>many=True</code> flag to the serializer arguments.</p>
|
|
<pre><code>serializer = SnippetSerializer(Snippet.objects.all(), many=True)
|
|
serializer.data
|
|
# [{'pk': 1, 'title': u'', 'code': u'foo = "bar"\n', 'linenos': False, 'language': u'python', 'style': u'friendly'}, {'pk': 2, 'title': u'', 'code': u'print "hello, world"\n', 'linenos': False, 'language': u'python', 'style': u'friendly'}]
|
|
</code></pre>
|
|
<h2 id="using-modelserializers">Using ModelSerializers</h2>
|
|
<p>Our <code>SnippetSerializer</code> class is replicating a lot of information that's also contained in the <code>Snippet</code> model. It would be nice if we could keep our code a bit more concise.</p>
|
|
<p>In the same way that Django provides both <code>Form</code> classes and <code>ModelForm</code> classes, REST framework includes both <code>Serializer</code> classes, and <code>ModelSerializer</code> classes.</p>
|
|
<p>Let's look at refactoring our serializer using the <code>ModelSerializer</code> class.
|
|
Open the file <code>snippets/serializers.py</code> again, and edit the <code>SnippetSerializer</code> class.</p>
|
|
<pre><code>class SnippetSerializer(serializers.ModelSerializer):
|
|
class Meta:
|
|
model = Snippet
|
|
fields = ('id', 'title', 'code', 'linenos', 'language', 'style')
|
|
</code></pre>
|
|
<p>One nice property that serializers have is that you can inspect all the fields in a serializer instance, by printing it's representation. Open the Django shell with <code>python manange.py shell</code>, then try the following:</p>
|
|
<pre><code>>>> from snippets.serializers import SnippetSerializer
|
|
>>> serializer = SnippetSerializer()
|
|
>>> print repr(serializer) # In python 3 use `print(repr(serializer))`
|
|
SnippetSerializer():
|
|
id = IntegerField(label='ID', read_only=True)
|
|
title = CharField(allow_blank=True, max_length=100, required=False)
|
|
code = CharField(style={'type': 'textarea'})
|
|
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')...
|
|
</code></pre>
|
|
<p>It's important to remember that <code>ModelSerializer</code> classes don't do anything particularly magical, they are simply a shortcut for creating serializer classes:</p>
|
|
<ul>
|
|
<li>An automatically determined set of fields.</li>
|
|
<li>Simple default implementations for the <code>create()</code> and <code>update()</code> methods.</li>
|
|
</ul>
|
|
<h2 id="writing-regular-django-views-using-our-serializer">Writing regular Django views using our Serializer</h2>
|
|
<p>Let's see how we can write some API views using our new Serializer class.
|
|
For the moment we won't use any of REST framework's other features, we'll just write the views as regular Django views.</p>
|
|
<p>We'll start off by creating a subclass of HttpResponse that we can use to render any data we return into <code>json</code>.</p>
|
|
<p>Edit the <code>snippets/views.py</code> file, and add the following.</p>
|
|
<pre><code>from django.http import HttpResponse
|
|
from django.views.decorators.csrf import csrf_exempt
|
|
from rest_framework.renderers import JSONRenderer
|
|
from rest_framework.parsers import JSONParser
|
|
from snippets.models import Snippet
|
|
from snippets.serializers import SnippetSerializer
|
|
|
|
class JSONResponse(HttpResponse):
|
|
"""
|
|
An HttpResponse that renders its content into JSON.
|
|
"""
|
|
def __init__(self, data, **kwargs):
|
|
content = JSONRenderer().render(data)
|
|
kwargs['content_type'] = 'application/json'
|
|
super(JSONResponse, self).__init__(content, **kwargs)
|
|
</code></pre>
|
|
<p>The root of our API is going to be a view that supports listing all the existing snippets, or creating a new snippet.</p>
|
|
<pre><code>@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)
|
|
|
|
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)
|
|
</code></pre>
|
|
<p>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 <code>csrf_exempt</code>. 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.</p>
|
|
<p>We'll also need a view which corresponds to an individual snippet, and can be used to retrieve, update or delete the snippet.</p>
|
|
<pre><code>@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()
|
|
return JSONResponse(serializer.data)
|
|
return JSONResponse(serializer.errors, status=400)
|
|
|
|
elif request.method == 'DELETE':
|
|
snippet.delete()
|
|
return HttpResponse(status=204)
|
|
</code></pre>
|
|
<p>Finally we need to wire these views up. Create the <code>snippets/urls.py</code> file:</p>
|
|
<pre><code>from django.conf.urls import patterns, url
|
|
from snippets import views
|
|
|
|
urlpatterns = [
|
|
url(r'^snippets/$', views.snippet_list),
|
|
url(r'^snippets/(?P<pk>[0-9]+)/$', views.snippet_detail),
|
|
]
|
|
</code></pre>
|
|
<p>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 <code>json</code>, 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.</p>
|
|
<h2 id="testing-our-first-attempt-at-a-web-api">Testing our first attempt at a Web API</h2>
|
|
<p>Now we can start up a sample server that serves our snippets.</p>
|
|
<p>Quit out of the shell...</p>
|
|
<pre><code>quit()
|
|
</code></pre>
|
|
<p>...and start up Django's development server.</p>
|
|
<pre><code>python manage.py runserver
|
|
|
|
Validating models...
|
|
|
|
0 errors found
|
|
Django version 1.4.3, using settings 'tutorial.settings'
|
|
Development server is running at http://127.0.0.1:8000/
|
|
Quit the server with CONTROL-C.
|
|
</code></pre>
|
|
<p>In another terminal window, we can test the server.</p>
|
|
<p>We can get a list of all of the snippets.</p>
|
|
<pre><code>curl http://127.0.0.1:8000/snippets/
|
|
|
|
[{"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"}]
|
|
</code></pre>
|
|
<p>Or we can get a particular snippet by referencing its id.</p>
|
|
<pre><code>curl http://127.0.0.1:8000/snippets/2/
|
|
|
|
{"id": 2, "title": "", "code": "print \"hello, world\"\n", "linenos": false, "language": "python", "style": "friendly"}
|
|
</code></pre>
|
|
<p>Similarly, you can have the same json displayed by visiting these URLs in a web browser.</p>
|
|
<h2 id="where-are-we-now">Where are we now</h2>
|
|
<p>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.</p>
|
|
<p>Our API views don't do anything particularly special at the moment, beyond serving <code>json</code> responses, and there are some error handling edge cases we'd still like to clean up, but it's a functioning Web API.</p>
|
|
<p>We'll see how we can start to improve things in <a href="../2-requests-and-responses">part 2 of the tutorial</a>.</p>
|
|
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