django restframework 教程之Serialization(序列化)

介绍

本教程将会通过创建一个简单的粘贴代码项目，突出显示WebAPI，过程中，会介绍组成REST框架的各种组件，让你全面了解如何配合使用。

环境设置

建议使用virtualenv建立新的虚拟环境，确保本项目所依赖的任何包和其他环境保持隔离

virtualenv env
source env/bin/activate

现在在新的虚拟环境中安装必须的包

pip install django
pip install djangorestframework
pip install pygments  #代码高亮使用

创建项目

我们将创建名为tutorial的项目，在项目中创建名为snippets的app

django-admin.py startproject tutorial
cd tutorial
python manage.py startapp snippets

最后我们需要在settings.py的INSTALLED_APPS配置里注册我们的snippetsapp和rest_frameworkapp

INSTALLED_APPS = [
	...
    'rest_framework',
    'snippets.apps.SnippetsConfig',
]

注意：如果使用的django版本低于1.9，直接使用snippets 来代替snippets.apps.SnippetsConfig即可

创建model

下面创建snippets所使用的数据库表用来存储代码

from django.db import models

from pygments.lexers import get_all_lexers
from pygments.styles import get_all_styles

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())


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)

    class Meta:
        ordering = ('created',)

然后我们需要在数据库中创建数据库表，生成表结构

python manage.py makemigrations snippets
python manage.py migrate

创建序列化的类

首先我们需要为api提供序列化和反序列化的方法，将snippet实例转为json等方式呈现数据，我们可以使用Serializer达到这一目的, Serializer和django forms十分相似. 我们在snippetapp下新建serializers.py文件

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):
        """
        新建Snippet实例
        """
        return Snippet.objects.create(**validated_data)

    def update(self, instance, validated_data):
        """
        更新Snippet示例
        """
        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

serializer的首先定义了序列化和反序列化的字段，其次create()和update()方法定义了当调用serializer.save()时如何对实例进行创建或修改
serializer和django的form非常类似，而且包括一些类似的验证字段的方法，如required,max_lengthanddefault.

使用Serializers

我们使用django的shell 环境来简单的测试Serializers

创建两个snippet实例

python3 manage.py shell


>>> 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()
>>> snippet2 = Snippet(code='print "hello, world"\n')
>>> snippet2.save()

序列化其中一个实例

>>> serializer = SnippetSerializer(snippet2)
>>> serializer.data
{'linenos': False, 'id': 2, 'code': 'print "hello, world"\n', 'language': 'python', 'style': 'friendly', 'title': ''}

我们已经将snippet2序列化为一个python的基本数据类型，现在我们生成json数据

>>> content = JSONRenderer().render(serializer.data)
>>> content
b'{"id":2,"title":"","code":"print \\"hello, world\\"\\n","linenos":false,"language":"python","style":"friendly"}'

反序列化更简单，首先将stream转为python基本类型

>>> from django.utils.six import BytesIO
>>> stream = BytesIO(content)
>>> data = JSONParser().parse(stream)
>>> data
{'linenos': False, 'id': 2, 'code': 'print "hello, world"\n', 'language': 'python', 'style': 'friendly', 'title': ''}

然后，我们将其转换为snippet实例

>>> serializer = SnippetSerializer(data=data)
>>> serializer.is_valid()
True
>>> serializer.validated_data
OrderedDict([('title', ''), ('code', 'print "hello, world"'), ('linenos', False), ('language', 'python'), ('style', 'friendly')])
>>> serializer.save()
<Snippet: Snippet object>

我们也可以序列化querysets对象来代替model instances，因此在序列化的时候需要添加many=True参数

>>> serializer = SnippetSerializer(Snippet.objects.all(), many=True)
>>> serializer.data
[OrderedDict([('id', 1), ('title', ''), ('code', 'foo = "bar"\n'), ('linenos', False), ('language', 'python'), ('style', 'friendly')]), OrderedDict([('id', 2), ('title', ''), ('code', 'print "hello, world"\n'), ('linenos', False), ('language', 'python'), ('style', 'friendly')]), OrderedDict([('id', 3), ('title', ''), ('code', 'print "hello, world"'), ('linenos', False), ('language', 'python'), ('style', 'friendly')])]

使用ModelSerializers

我们的SnippetSerializer类很多信息和Snippet model中是重复的，为了保证我们代码的简洁，减少重复代码，类似于django的提供的form和modelform，REST framework也提供了Serializerand ModelSerializer
下面使用ModelSerializer重构我们的serializer，重新打开serializers.py，使用下面代码替换掉SnippetSerializer类

class SnippetSerializer(serializers.ModelSerializer):
    class Meta:
        model = Snippet
        fields = ('id', 'title', 'code', 'linenos', 'language', 'style')

serializers有一个不错的属性是，可以通过print函数来打印它 表示检查序列化实例中的所有字段

>>> from snippets.serializers import SnippetSerializer
>>> serializer = SnippetSerializer()
>>> print(repr(serializer))

重要的是要记住 ModelSerializer 不做任何格外的配置，它只是创建序列化类的快捷方式：

• 根据model里的字段自动定义字段集
• 简单的实现 create() and update() 方法

在django 视图中使用我们的Serializer

让我们看看我们如何使用我们新的Serializer类编写一些API视图。目前我们不使用任何REST框架的其他功能，我们只是将视图写为常规Django视图。
我们将开始通过创建一个HttpResponse子类用来返回任何形式的数据，如json；
编辑views.py

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)


@csrf_exempt
def snippet_list(request):
    """
    列出所有的实例，或创建一个新的实例.
    """
    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)

注意我们在post测试的时候无法获取到Django的csrf token，所以使用@csrf_exempt将此视图排除，不在检查csrf token
我们将还需要一个与单个代码段对应的视图，并且可以用来检索、更新和删除代码段

@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)

最后，我们需要配置url信息,在snippetapp下，新建urls.py

from django.conf.urls import url
from snippets import views

urlpatterns = [
    url(r'^snippets/$', views.snippet_list),
    url(r'^snippets/(?P<pk>[0-9]+)/$', views.snippet_detail),
]

我们也需要在tutorial项目的urls.py下将snippetapp的url配置加载进去

from django.conf.urls import url, include

urlpatterns = [
    url(r'^', include('snippets.urls')),
]

尝试测试我们的web api

启动我们的django server

python manage.py runserver

Performing system checks...

System check identified no issues (0 silenced).
February 04, 2017 - 08:38:55
Django version 1.10, using settings 'tutorial.settings'
Starting development server at http://127.0.0.1:8000/
Quit the server with CONTROL-C.

最后使用curl 进行测试

curl -s http://127.0.0.1:8000/snippets/ | jq .
[
  {
    "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"
  }
]

也可以指定id进行查询

curl -s http://127.0.0.1:8000/snippets/1/ | jq .
{
  "id": 1,
  "title": "",
  "code": "foo = \"bar\"\n",
  "linenos": false,
  "language": "python",
  "style": "friendly"
}

源文参考：http://www.django-rest-framework.org/tutorial/1-serialization/#testing-our-first-attempt-at-a-web-api