Rest framework 学习（1）序列化

序列化定义

将一种对象的状态信息装换成可以存储或者可以传输形式的过程。比如将模型类转换成JSON数据,整个过程将序列化(序列化和反序列化执行的过程相似的,也就是可以封装代码)

创建新的APP

python manage.py startapp snippets

• 配置app

# 配置
INSTALLED_APPS = (
    ...
    'rest_framework',
    'snippets.apps.SnippetsConfig',
)

写一个代码片段model 带代码高亮

# snippets/models.py
# pygment 用于代码高亮

from django.db import models
from pygments.lexers import get_all_lexers  # 词法分析程序
from pygments.styles import get_all_styles  # 高亮样式


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',)

代码段模型创建初始迁移，并首次同步数据库。

python manage.py makemigrations snippets
python manage.py migrate

创建几个代码片段

# 进入shell
python manage.py shell

# 创建代码片段对象

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()

# 来看看序列化其中一个实例

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

# 已将模型实例转换为Python本机数据类型
content = JSONRenderer().render(serializer.data)
content
# b'{"id": 2, "title": "", "code": "print(\\"hello, world\\")\\n", "linenos": false, "language": "python", "style": "friendly"}'

# 反序列化是类似的 首先，我们将流解析为Python本机数据类型

import io

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


# 本机数据类型还原为完全填充的对象实例

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()
# 

# 查询多少对象时，需要设置many=True

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

这是我们建议采用的模式，与Django提供Form类和ModelForm类的方式相同，REST框架包括Serializer类和ModelSerializer类。现在我们用ModelSerializers重构snippets/serializers.py

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

 打开shell 我们验证一下：

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

## repr() 函数将对象转化为供解释器读取的形式
# SnippetSerializer():
#    id = IntegerField(label='ID', read_only=True)
#    title = CharField(allow_blank=True, max_length=100, required=False)
#    code = CharField(style={'base_template': 'textarea.html'})
#    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')...

 ModelSerializer 在这里主要做两件事：

• 自动确定的字段集。
• 简单默认实现create()和update()方法

使用Serializer编写常规Django视图

编辑snippets/views.py文件，并添加以下内容

# snippets/views.py

from django.http import HttpResponse, JsonResponse
from django.views.decorators.csrf import csrf_exempt
from rest_framework.parsers import JSONParser
from snippets.models import Snippet
from snippets.serializers import SnippetSerializer

@csrf_exempt  # 跳过csrf认证
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)

添加snippets/urls.py

# snippets/urls.py

from django.urls import path
from snippets import views

# root-snippets/
urlpatterns = [
    path('snippets/', views.snippet_list),
    path('snippets//', views.snippet_detail),
]

修改tutorial/urls.py

urlpatterns = [
    path('', include(router.urls)),
    # 包含默认登录和注销,身份验证
    path('api-auth/', include('rest_framework.urls', namespace='rest_framework')),
    path('root-snippets/', include('snippets.urls')),
]

启动项目，这里可以用Postman测试也可以直接通过浏览器访问。

访问：
http://127.0.0.1:8000/root-snippets/snippets/

http://127.0.0.1:8000/root-snippets/snippets/2/

访问结果如下：

个人感受：

这部分相对与采用rest 框架的View来说， 直接使用django.http.JsonResponse+django.core.serializers（以前我就是这样干的）能实现更加灵活的自定义接口API。

现在对rest-framework 和直接JsonResponse自己封装的json格式response的区别不太清楚。

前者可能对比较规范的model开发接口会方便些，复杂些的估计够呛（目前学的还不深入），但采用的设计思想都是一样的，都是有浏览器发ajax请求，服务器不在返回渲染好的html以及模型数据了，而是json数据，将渲染的任务给了浏览器，这也是前后端分离的原理。