如何为自定义类型定义序列化，用作自定义 Django 字段的值

Question

我创建了自己的自定义 models.TextField 子类，它将类作为其值并将这些值编码为数据库中给定类的 CODE 属性。到目前为止，所有这些都有效，但我想使用 Django-reversion，它会在每次进行更改时序列化模型并将模型保存在版本表中。我将其用于审核我的应用程序。

Reversion 无法序列化我分配给自定义字段的值，声称它们不可序列化。如何为我的对象定义序列化方法？我不能只定义一个 DjangoJSONEncoder 子类（Django 默认用来序列化的类），因为我无法控制调用其序列化方法的代码，因为它是 Django-reversion 的一部分。这是堆栈跟踪，最终在 Python 的默认 json 编码器中失败：

ERROR: Could not save initial version for AccessCircuitRTTicket 3.
Traceback (most recent call last):
  File "./manage.py", line 12, in <module>
    execute_from_command_line(sys.argv)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/management/commands/createinitialrevisions.py", line 87, in handle
    self.create_initial_revisions(app, model_class, comment, batch_size, verbosity)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/management/commands/createinitialrevisions.py", line 123, in create_initial_revisions
    default_revision_manager.save_revision((obj,), comment=comment)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/revisions.py", line 430, in save_revision
    for obj in objects
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/revisions.py", line 430, in <genexpr>
    for obj in objects
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/revisions.py", line 108, in get_version_data
    "serialized_data": self.get_serialized_data(obj),
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/reversion/revisions.py", line 91, in get_serialized_data
    fields = list(self.get_fields_to_serialize()),
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/serializers/__init__.py", line 122, in serialize
    s.serialize(queryset, **options)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/serializers/base.py", line 58, in serialize
    self.end_object(obj)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/serializers/json.py", line 52, in end_object
    cls=DjangoJSONEncoder, **self.json_kwargs)
  File "/usr/lib/python2.7/json/__init__.py", line 181, in dump
    for chunk in iterable:
  File "/usr/lib/python2.7/json/encoder.py", line 427, in _iterencode
    for chunk in _iterencode_dict(o, _current_indent_level):
  File "/usr/lib/python2.7/json/encoder.py", line 401, in _iterencode_dict
    for chunk in chunks:
  File "/usr/lib/python2.7/json/encoder.py", line 401, in _iterencode_dict
    for chunk in chunks:
  File "/usr/lib/python2.7/json/encoder.py", line 435, in _iterencode
    o = _default(o)
  File "/home/sgalbraith/.python_virtualenvs/unleash/local/lib/python2.7/site-packages/django/core/serializers/json.py", line 104, in default
    return super(DjangoJSONEncoder, self).default(o)
  File "/usr/lib/python2.7/json/encoder.py", line 177, in default
    raise TypeError(repr(o) + " is not JSON serializable")
TypeError: <class 'console.broadband.enumerations.ProvisioningTicket'> is not JSON serializable

在 LazyEncoder 的定义及其前面的文本中，对答案 here 有一个模糊的建议。

Answer 1

经过一天的努力，我想出了一个答案。我对它不是特别满意，因为它使责任远离我想要序列化的类型。一个更好的答案会很好！这就是我得到的...

请注意，我拥有的 Django 自定义字段的值是类（即它们具有类型的类型）并且是 EnumMember 的子类，具有一个名为 CODE 的类成员，它给出了它们的字符串表示形式。

我创建了以下模块 crm.serializers.json 并将设置中的 SERIALIZATION_MODULES 设置为

SERIALIZATION_MODULES = {
    'json': 'crm.serializers.json',
}

crm.serializers.json 代码如下：

# Avoid shadowing the standard library json module
from __future__ import absolute_import

from django.core.serializers.json import DjangoJSONEncoder, Serializer, \
    Deserializer as DjangoDeserializer
from django.utils.encoding import force_text

from crm.enum import EnumMember
import json

####################################################################################################
#
#    Extension of Django serialization capability so that apps such as Django-reversion can deal
#    with custom fields.
#
####################################################################################################
class Serializer(Serializer):

    # Override
    # This is a copy paste of the superclass method, but with cls=ExtendedJSONEncoder
    # instead of cls=DjangoJSONEncoder below
    def end_object(self, obj):
        # self._current has the field data
        indent = self.options.get("indent")
        if not self.first:
            self.stream.write(",")
            if not indent:
                self.stream.write(" ")
        if indent:
            self.stream.write("\n")
        json.dump(self.get_dump_object(obj), self.stream,
                  cls=ExtendedJSONEncoder, **self.json_kwargs)
        self._current = None
        pass


Deserializer = DjangoDeserializer


class ExtendedJSONEncoder(DjangoJSONEncoder):
    """
    Provides default serialization for custom data types as well as default ones.
    """
    def default(self, obj):
        if type(obj) == type and issubclass(obj, EnumMember):
            return obj.CODE
        else:
            return super(ExtendedJSONEncoder, self).default(obj)

Answer 2

不能肯定地说，因为我没有看到您的 TextField 子类，但是
value_to_string(self, obj)
在序列化框架中使用，你可以重写Field类的这个方法。

喜欢这个

def value_to_string(self, obj):
    return self.value_from_object(obj.CODE)

对于反序列化，请确保您的 to_python(self, value) 工作正常