Serializing and Deserializing Django objects(序列化以及反序列化Django对象)

Django’s serialization framework provides a mechanism for “translating” Django models into other formats. Usually these other formats will be text-based and used for sending Django data over a wire, but it’s possible for a serializer to handle any format (text-based or not).（Django序列化框架提供将模型转换成其他格式的机制，通常转换后的格式主要是用来传输的基于文本的数据，事实上Django能够处理任何数据转换，无论是基于文本的还是非文本的），以下为常用的转换格式：

Identifier	Information
xml	Serializes to and from a simple XML dialect.
json	Serializes to and from JSON.
yaml	Serializes to YAML (YAML Ain’t a Markup Language). This serializer is only available if PyYAML is installed.

If you just want to get some data from your tables into a serialized form, you could use the dumpdata management command.（如果想要直接从数据表中获取数据然后序列化成合适的格式，可以使用dumpdata 管理命令）

以序列化为XML格式的数据为例引入讲解基础知识：

>>> from django.core import serializers
>>> data = serializers.serialize("xml", SomeModel.objects.all())

Subset of fields(子集字段的序列化)

>>> data = serializers.serialize('xml',User.objects.all(), fields=('nickname','first_name','last_name'))
>>> data
'\n<django-objects version="1.0"><object model="userapp.user" pk="lockey23"><field name="first_name" type="CharField">Yangfield><field name="last_name" type="CharField">Chengfield>object>django-objects>'

This is useful if you want to serialize data directly to a file-like object (which includes an HttpResponse):（对于想要将数据序列化为类似文件的对象，可以使用以下方式）

py3) [root@7-o-1 iledu]# python manage.py shell
>>> from userapp.models import User
>>> from django.core import serializers
>>> XMLSerializer = serializers.get_serializer("xml")
>>> xml_serializer = XMLSerializer()
>>> with open("file.xml", "w") as out:
...     xml_serializer.serialize(User.objects.all(),stream=out)
(py3) [root@7-o-1 iledu]# cat file.xml 

<django-objects version="1.0"><object model="userapp.user" pk="lockey23"><field name="first_name" type="CharField">Yangfield><field name="last_name" type="CharField">Chengfield><field name="email" type="CharField"><None>None>field><field name="password" type="CharField"><None>None>field><field name="role" type="CharField">teammatefield><field name="avatar" type="CharField">/static/avatar/default.jpgfield><field name="created_at" type="DateTimeField"><None>None>field><field name="updated_at" type="DateTimeField"><None>None>field><field name="last_login_at" type="DateTimeField"><None>None>field>object>django-objects>(py3)

Note

Calling get_serializer() with an unknown format will raise a django.core.serializers.SerializerDoesNotExist exception.
在未指定格式化参数的情况下调用get_serializer()将会引发一个django.core.serializers.SerializerDoesNotExist 异常

序列化后的数据格式：

>>> for obj in serializers.deserialize("xml", data):
...     print(type(obj))
... 
'django.core.serializers.base.DeserializedObject'>

Inherited models（继承模型的序列化）
对于类似以下模型：

class Place(models.Model):
    name = models.CharField(max_length=50)

class Restaurant(Place):
    serves_hot_dogs = models.BooleanField(default=False)

当我们使用以下方法进行序列化的时候：

data = serializers.serialize('xml', Restaurant.objects.all())

the fields on the serialized output will only contain the serves_hot_dogs attribute. The name attribute of the base class will be ignored.（序列化后的输出将只包含serves_hot_dogs 属性，基类的name属性将被忽略），如果想要将基类的属性也进行序列化的话那么应该操作如下：

all_objects = list(Restaurant.objects.all()) + list(Place.objects.all())
data = serializers.serialize('xml', all_objects)

数据的反序列化：

>>> u = User.objects.all()
>>> u
]>
>>> u.delete()
(1, {'userapp.User': 1})
>>> u

>>> for obj in serializers.deserialize("xml", data):
...     obj.save()
... 
>>> u
]>

As you can see, the deserialize function takes the same format argument as serialize, a string or stream of data, and returns an iterator.（如上所见，反序列化函数接受如序列化一样的参数，一个字符串代表数据格式，以及需要反序列化的数据，结果返回一个迭代器）

我们可以使用：

DeserializedObject.save()【即上栗中的obj.save()】将对象保存到数据库中去

note

The Django object itself can be inspected as deserialized_object.object. If fields in the serialized data do not exist on a model, a DeserializationError will be raised unless the ignorenonexistent argument is passed in as True:
Django 对象自己会检查反序列化的数据是否匹配对应模型，如果不匹配的话，一个DeserializationError 异常将被抛出（条件是ignorenonexistent 参数设置为True）,如下例：

serializers.deserialize("xml", data, ignorenonexistent=True)

序列化为json格式：

user_list = serializers.serialize('json', User.objects.all())

对于一些定制类型的数据序列化为json需要做特殊处理，eg:

from django.core.serializers.json import DjangoJSONEncoder

class LazyEncoder(DjangoJSONEncoder):
    def default(self, obj):
        if isinstance(obj, YourCustomType):
            return str(obj)
        return super().default(obj)

You can then pass cls=LazyEncoder to the serializers.serialize() function:

from django.core.serializers import serialize

serialize('json', SomeModel.objects.all(), cls=LazyEncoder)

序列化为yaml格式：

pip install PyYAML

>>> from django.core import serializers
>>> from userapp.models import User
>>> data = serializers.serialize('yaml',User.objects.all(), fields=('nickname','first_name','last_name'))
>>> data
'- model: userapp.user\n  pk: lockey23\n  fields: {first_name: Yang, last_name: Cheng}\n'
>>>