django rest-farme-work 的使用(2)

serialization （序列化）

本測試項目例子地址爲：

tomchristie/rest-framework-tutorial

開始構建一個新的程序

建立一個新的環境

virtualenv env
source env/bin/activate

安裝相應的包

pip install django
pip install djangorestframework
pip install pygments  # We'll be using this for the code highlighting(代碼高亮)

建立一個項目

cd ~
django-admin.py startproject tutorial
cd tutorial

創建一個App

python manage.py startapp snippets

在settings 文件中添加下配置

```INSTALLED_APPS = (

'rest_framework',
'snippets.apps.SnippetsConfig',

```

在 snippets/models.py 中添加

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',)

咱們還須要爲咱們的片斷模型建立初始遷移，並首次同步數據庫。

python manage.py makemigrations snippets
python manage.py migrate

建立一個序列化類

咱們須要開始使用Web API的第一件事就是提供一種將代碼片斷實例序列化和反序列化爲表示形式的方法json。咱們能夠經過聲明與Django的表單很是類似的序列化器來實現這一點。在snippets名爲的目錄中建立一個文件serializers.py並添加如下內容。

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

序列化器類的第一部分定義了序列化/反序列化的字段。該create()和update()方法定義實例如何徹底成熟的建立或修改時調用serializer.save()

甲串行類很是相似於一個Django Form類，而且包括關於各個字段相似的驗證標記，如required，max_length和default。

字段標誌還能夠控制在某些狀況下應該如何顯示序列化程序，例如在呈現爲HTML時。{'base_template': 'textarea.html'}上面的標誌等同於widget=widgets.Textarea在Django Form類上使用。這對於控制如何顯示可瀏覽的API特別有用，正如咱們將在本教程後面看到的。

咱們實際上也能夠經過使用這個ModelSerializer類節省一些時間，咱們稍後會看到，但如今咱們將保持咱們的序列化器定義清晰。

測試序列化類

在咱們繼續以前，咱們將熟悉使用咱們的新Serializer類。咱們來看看Django 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()

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

咱們來看看序列化其中的一個實例。

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

在前面上，咱們已經將模型實例轉換爲Python本地數據類型。爲了完成序列化過程，咱們將數據渲染到json

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

反序列化

from django.utils.six import BytesIO

stream = BytesIO(content)
data = JSONParser().parse(stream)

將本地的數據類型恢復填充到數據庫

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

注意API與表單的工做方式類似。當咱們開始編寫使用咱們的序列化器的視圖時，類似性應該變得更加明顯。

咱們也能夠序列化查詢集而不是模型實例。爲此，咱們只需many=True在序列化參數中添加一個標誌便可

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

使用ModelSerializer

前面咱們SnippetSerializer類複製Snippet模型中包含的大量信息。若是咱們能夠保持咱們的代碼更加簡潔。

讓咱們看看使用ModelSerializer類重構咱們的序列化程序。snippets/serializers.py再次打開文件，把SnippetSerializer類從新定義，以下

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

記住ModelSerializer類不要作任何特別的事情是很重要的，它們只是建立序列化類的一個捷徑。

• 自動肯定的一組字段。
• 簡單的默認實現create()和update()方法。

使用咱們的序列化程序編寫常規的Django視圖

編輯snippets/views.py文件，並添加如下內容。

from django.http import HttpResponse, JsonResponse
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
##ddvim

@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)

@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)

配置url

from django.conf.urls import url, include
from snippets import views
# Additionally, we include login URLs for the browsable API.
urlpatterns = [
    url(r'^snippets/$',views.snippet_list),
    url(r'^snippets/(?P<pk>[0-9]+)/$',views.snippet_detail),

]

安裝調試工具

pip install httpie

測試

http http://127.0.0.1:8000/snippets/

HTTP/1.1 200 OK
...
[
  {
    "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"
  }
]

http http://127.0.0.1:8000/snippets/2/

HTTP/1.1 200 OK
...
{
  "id": 2,
  "title": "",
  "code": "print \"hello, world\"\n",
  "linenos": false,
  "language": "python",
  "style": "friendly"
}