Django-rest-framework (一)、序列化

序列化

django-rest-framework serializer可以很方便的实现model对象的序列化，对前端传递的数据进行验证等等，功能与django原生的form很相似，但是却比form更强大，下面体验一下。

开始

安装：

pip install django-rest-framework

创建一个新django项目：

django-admin.py startproject rest
python  manage.py startapp snippet

rest/settings.py添加app：

INSTALLED_APPS  =   (
                ...
                'rest_framework',
                'snippets',
)

创建一个model
snippet/models.py:

from django.db import models

# Create your models here.
LANGUAGE_CHOICES = (
    ('1', 'cn'),
    ('2', 'us')
)

STYLE_CHOICES = (
    ('1', 't1'),
    ('2', 't2')
)

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= '1',max_length=5)
    style = models.CharField(choices=STYLE_CHOICES, default='1',max_length=5)

    class Meta:
        ordering = ('created',)

创建serializer.py文件：
snippet/serializer.py:

from rest_framework import serializers
from snippet.models import Snippet,LANGUAGE_CHOICES,STYLE_CHOICES

class Snippetserializer(serializers.Serializer):
    pk = serializers.IntegerField(read_only=True)
    title = serializers.CharField(required=False, allow_blank=True, max_length=32)
    code = serializers.CharField(style={'base_template': 'textarea.html'})
    linenos = serializers.BooleanField(required=False)
    language = serializers.ChoiceField(choices=LANGUAGE_CHOICES, default= '1')
    style = serializers.ChoiceField(choices=STYLE_CHOICES,  default='1')

    def create(self, validated_data):
        return Snippet.objects.create(**validated_data)

    def update(self, instance, 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

创建表结构：

python manage.py makemigrations
python manage.py migrate

开始使用django命令行,写一些序列化测试代码：

$ python manage.py shell
>>> from snippet.models import Snippet
>>> from snippet.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()
>>>> obj = Snippetserializer(snippet)
>>> obj.data
{'language': '1', 'pk': 2, 'title': '', 'code': 'print"hello,world"\n', 'linenos': False, 'style': '1'}
>>> obj['code']
<BoundField value=print"hello,world"
 errors=None>

>>> content=JSONRenderer().render(obj.data)
>>> stream = BytesIO(content)
>>> content1 = JSONParser().parse(stream)
>>> content2=JSONRenderer().render(obj.data).decode()
>>> print(content)
b'{"pk":2,"title":"","code":"print\\"hello,world\\"\\n","linenos":false,"language":"1","style":"1"}'
>>> type(obj)
<class 'snippet.serializers.Snippetserializer'>
>>> type(obj.data)
<class 'rest_framework.utils.serializer_helpers.ReturnDict'>
>>> type(content)
<class 'bytes'>
>>> type(stream)
<class '_io.BytesIO'>
>>> content2=JSONRenderer().render(obj.data).decode()
>>> type(content1)
<class 'dict'>
>>> type(content2)
<class 'str'>
>>> type(json.loads(content2))
<class 'dict'>

#可以看到，由rest serializer处理后的model对象变成了其的serializer对象，使用obj.data方法可以取出其内容，然后使用jsonrender方法将数据渲染成byte格式的json字符串，可以再通过bytesIO转换和通过jsonparser方法转换回dict格式。也可以直接在jsonrender的时候使用decode()方法处理，直接返回json格式str，然后通过json.loads()方法反序列化成dict格式。

同时，作为为django量身定制的框架，serializer也支持queryset的序列化（原生json模块不支持序列化queryset），在序列化的时候添加一个many = True参数即可：

>>> serializer= Snippetserializer(Snippet.objects.all(),many=True)
>>> serializer.data
[OrderedDict([('pk', 1), ('title', ''), ('code', 'foo="bar"\n'), ('linenos', False), ('language', '1'), ('style', '1')]), OrderedDict([('pk', 2), ('title', ''), ('code', 'print"hello,world"\n'), ('linenos', False), ('language', '1'), ('style', '1')])]
>>> serializer.data[0]
OrderedDict([('pk', 1), ('title', ''), ('code', 'foo="bar"\n'), ('linenos', False), ('language', '1'), ('style', '1')])
>>> serializer.data[0]['code']
'foo="bar"\n'

梳理一下：
1.model对象通过serializer方法序列化成新的对象obj,obj.data可以取出此对象的各items
2.jsonrender方法可以将obj.data渲染成byte格式对象，再通过byteIO处理可以转换成python的byte格式数据流。也可以decode成json风格str类型。
3.jsonparser方法可以将数据流(json风格str)反处理成dict格式

ModelSerializer

如modelform一样，restframework同样存在可以直接基于model关联，进行field字段关联验证等功能的模块，ModelSerializer.

改写snippet/serializer.py：

from rest_framework import serializers
from snippet.models import Snippet

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

写一个视图views.py，提供list查询、提交，单个对象查询、修改、删除方法：

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 snippet.models import Snippet
from snippet.serializers import SnippetSerializer



class JSONResponse(HttpResponse):

    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):
    '''
    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)


@csrf_exempt
def snippet_detail(request,pk):

    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)

定义urls规则关联视图函数：
urls.py:

from django.conf.urls import url
from django.contrib import admin
from snippet import views as snippet_views

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

验证测试：
开启服务：

python manage.py runserver

测试：

$ curl http://127.0.0.1:8000/snippets/
[{"id":1,"title":"","code":"foo=\"bar\"\n","linenos":false,"language":"1","style":"1"},{"id":2,"title":"","code":"print\"hello,world\"\n","linenos":false,"language":"1","style":"1"}]ywq@ywq-ThinkPad-E470:/usr/local/myutils$ curl http://127.0.0.1:8000/snippets/detail/1
$ curl http://127.0.0.1:8000/snippets/detail/1/
{"id":1,"title":"","code":"foo=\"bar\"\n","linenos":false,"language":"1","style":"1"}

简单的接口OK了