Django Rest Framework学习进程(一) 序列化

　　首先是巴拉巴拉的开场白:博主是名在校的大专生，今年大二了，主学Python，现在想通过写博客的形式来记录我学习的过程，从而来督促我自己，本学习过程是通过阅读官方文档来实现的，官网文档的网址为:https://www.django-rest-framework.org

　　1.准备工作

　　　首先，需要安装依赖包有:django、djangorestframework、pygments,这里通过pip命令直接安装,至于环境的配置问题，这里就不再进行赘述了,安装命令如下:

pip install django //本文基于django1.11版本来做
pip install djangorestframework
pip install pygments  //实现代码的高亮

 　2.新建一个名字tutorial的项目

django-admin startproject tutorial

　　3.创建一个APP,名字叫snippets

//执行startapp命令来创建应用
python manage.py startapp snippets

//编辑tutorial/settings.py文件,将snippets和rest_framework加入到INSTALLED_APPS当中
INSTALLED_APPS = {
    ...
    'snippets',
    'rest_framework'
}

　　4.创建一个snippets model

//在snippets/models.py中,写入以下代码:
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',)

　　5.执行数据库迁移命令

python manage.py makemigrations snippets
python manage.py migrate

　　6.创建一个序列化类(SnippetSerializer)

#这个类的功能和Django中的forms有点类似
//在snippets下,新建一个serializers.py文件
//在snippets/serializers.py中,写入以下代码:

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


class SnippetSerializer(serializers.Serializer):
    """
    序列化器类的第一部分定义了序列化/反序列化的字段
    create()和update()方法定义了在调用serializer.save()时如何创建和修改完整的实例。
    """
    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):
        """
        给定经过验证的数据,创建并返回一个新的"Snippet"实例
        """
        return Snippet.objects.create(**validated_data)

    def update(self, instance, validated_data):
        """
        根据提供的验证过的数据更新和返回一个已经存在的`Snippet`实例
        """
        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

　　7.启动Django shell

//启动shell
python 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

#实例化Snippet这个类,增加相应的值并作保存
snippet = Snippet(code='foo = "bar"\n')
snippet.save()

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

　　8.序列化与反序列化

#这里的snippet为上面实例出来的snippet对象
serializer = SnippetSerializer(snippet)
serializer.data
##执行结果:{'id': 2, 'title': '', 'code': 'print("hello, world")\n', 'linenos': False, 'language': 'python', 'style': 'friendly'}

#将实例snippet转换为Python原生数据类型,为了完成这个序列化的过程,需将返回的serializer.data转换为JSON格式
content = JSONRenderer().render(serializer.data)
content
##执行结果: b'{"id": 2, "title": "", "code": "print(\\"hello, world\\")\\n", "linenos": false, "language": "python", "style": "friendly"}'

#反序列化(还原序列化)的过程是类似的
#首先引入io模块，因为content是bytes类型的数据,所以这里调用BytesIO()这个方法,将这个流(stream)转换为Python原生数据类型
import io
stream = io.BytesIO(content)
data = JSONParser().parse(stream)
data

 　9.将Python原生数据类型转为实例对象

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>　

　　10.序列化查询结果集

#上面在序列化的过程中,传的是Snippet对象，其实还可以传querysets对象
#只需要加入"many=True"即可
serializer = SnippetSerializer(Snippet.objects.all(), many=True)
serializer.data
##结果为: [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')])]

　　11.使用ModelSerializer类

#在snippets/serializers.py中,将SnippetSerializer类替换为以下内容
class SnippetSerializer(serializers.ModelSerializer):
    class Meta:
        model = Snippet
        fields = ('id', 'title', 'code', 'linenos', 'language', 'style')

#运行python manage.py shell,写下以下代码:
#通过打印实例的属性(representation)来查看所有字段
from snippets.serializers import SnippetSerializer
serializer = SnippetSerializer()
print(repr(serializer))

　　需要注意的是,ModelSerializer类没有做什么特别的事情,它只是一个创建序列化类的捷径：1.实现一组自动确定的字段  2.默认简单地实现create()和update()这两个方法

　　12.使用Serializer来编写Django的视图

#首先导入如下包
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


#加上@csrf_exempt代表这个视图不需要csrf令牌也能访问
#创建一个根视图函数,用来列出所有现有的snippet或创建一个新的snippet
def snippet_list(request):
    """
    列出所有的code snippets,或创建一个新的snippet
    """
    if request.method == "GET":
        snipppets = Snippet.objects.all()
        serializer = SnippetSerializer(snipppets,many=True)
        #将数据类型转为正常的实例的对象,通过data属性输出出来
        return JsonResponse(serializer.data,safe=False)

    elif request.method == "POST":
        #对传过来的request做处理(假设这里传过来的是json格式的请求)
        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):
    """
    获取,更新或删除一个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(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)

　　13.编写url路径

#首先,先在snippets下创建一个urls.py文件,写入以下代码:
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),
]

#接着,在tutorial/urls.py中,写入以下代码:
from django.conf.urls import url,include

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^',include('snippets.urls'))

]

　　14.测试API

#首先,安装一个依赖包,名字叫httpie,httpie是用Python编写的用户友好的http客户端
pip install httpie

#接着,使用python manage.py runserver 命令来启动Django
#在网址中输入:http://127.0.0.1:8000/snippets/，可获取所有数据

#输入http://127.0.0.1:8000/snippets/2/,可获取指定的数据

#这样,最开始的第一步就完成啦，完结撒花先嘿嘿嘿~