[Django rest-framework] 1-Serialization

个人粗浅的理解，欢迎批评指正

什么是序列化？

　　后端任务无非对数据库的增查删改，操作数据库无非操作字段，序列化可以让我们轻松的对数据库增（serializer.create）改（serilaizer.update)的同时不用担心提交的key/value是否合法（serializer.is_valid）,并轻松的将dict 格式转为更通用的json格式（JSONRenderer）

什么是反序列化？

　　将json转为（JSONParser().parse(stream)）可序列化的dict（serializer(data=data)）

跟着教程走一波

先安装一下virtualenv

新建一个虚拟环境env

进入env虚拟环境

sudo apt-get install virtualenv
virtualenv env
source env/bin/activate

离开虚拟环境：deactivate

ps：如果使用pycharm IDE，在file-settings-Project：XXX-Project Interpreter,将项目解释器设置为虚拟环境中安装的python

在我们的虚拟环境中安装其他所需库

pip install django
pip install djangorestframework
pip install pygments # 用来高亮代码的库

创建项目，创建app

cd ~
django-admin.py startproject tutorial
cd tutorial

python manage.py startapp snippets

记得settings.INSTALLED_APPS中添加刚才创建的app

INSTALLED_APPS = (
    ...
    ‘rest_framework‘,
    ‘snippets.apps.SnippetsConfig‘,
)

django 创建一个django模型

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‘,)

有没有菜鸡跟我一样才发现，原来从模型这里就可以限制字段的可选值（choices）

Meta元类中的ordering是指quarySet排序按’created‘字段来

django的orm

操作下数据库

python manage.py makemigrations snippets
python manage.py migrate

重点到了，新建一个serializers.py 文件，并创建我们的序列化类

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

create和update是必须在子类中实现的方法，因为调用serializer.save()方法会用到他们

serializer类和django的model类很相似，可以在声明的时候限制字段的属性

接下来看看怎么使用序列化类

先打开django shell

python manage.py shell

然后创建两个数据

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()

接着：

1：序列化

serializer = SnippetSerializer(snippet)
serializer.data

# {‘id‘: 2, ‘title‘: u‘‘, ‘code‘: u‘print "hello, world"\n‘, ‘linenos‘: False, ‘language‘: u‘python‘, ‘style‘: u‘friendly‘}

2：转json

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

3：转dict

from django.utils.six import BytesIO

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

4：反序列化

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>

5：支持序列化多个数据

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‘)])]

看到这里感觉序列化就是将form对象转为dict格式，将quaryset转为OrderedDict

下节学习一下，正真更通用的ModelSerializers

参考资料：http://www.django-rest-framework.org/tutorial/1-serialization/#tutorial-1-serialization