Django 管理员 : object is not JSON serializable error on Custom Field Sub-classing JSONField

Question

我正在尝试通过将某些对象存储在 JSONFields 中来对支持 JSON API 的 Django Postgres 数据库进行去规范化:

https://docs.djangoproject.com/en/1.11/ref/contrib/postgres/fields/#jsonfield

我扩展了 django.contrib.postgres.fields.JSONField 字段以自动将数据序列化为 Python 对象。我这样做是为了围绕对象封装我的逻辑并强制执行存储在 JSONField 中的对象的结构。我在这里关注自定义模型字段的 Django 文档:

https://docs.djangoproject.com/en/1.11/howto/custom-model-fields/

我可以将我的对象存储在自定义 JSONField 中，并可以将它们作为 native Python 对象检索，但是，我破坏了管理控制台。当我尝试查看我的一个对象时，出现此错误:

TypeError: <core.fields.PostalAddress object at 0x7fdcfaade4e0> is not JSON serializable

我认为问题是内置的 json.dumps 函数不能很好地处理随机对象，所以我希望我可以在我的 PostalAddress 类中重写一些方法来让它很好地播放。

这是我的代码，虽然这是一个简单的地址案例，但我想将此模式应用于更复杂和有用的自定义 JSONField 用例，所以我希望在管理控制台中看到序列化的 JSON 并且能够编辑文本并保存。

字段.py

from django.contrib.postgres.fields import JSONField

class PostalAddress(object):
    def __init__(self, street='', city='', state='', postal_code=''):
        self.street = street
        self.city = city
        self.state = state
        self.postal_code = postal_code

def deserialize_address(address_dict):
    return PostalAddress(**address_dict)

def get_empty_address():
    return PostalAddress()

class PostalAddressField(JSONField):
    description = "A postal address"

    def __init__(self, *args, **kwargs):
        super(PostalAddressField, self).__init__(*args, **kwargs)

    def get_prep_value(self, value):
        if value is None:
            return value
        if isinstance(value, PostalAddress):
            return json.dumps(value.__dict__)
        return value

    def from_db_value(self, value, expression, connection, context):
        if value is None:
            return value
        return deserialize_address(value)

    def to_python(self, value):
        if isinstance(value, PostalAddress):
            return value
        if value is None:
            return value
        return deserialize_address(value)

模型.py

from django.db import models
from .fields import PostalAddressField, get_empty_address

class Person(models.Model):
    shipping_address = PostalAddressField(default = get_empty_address)

完整跟踪:

Request Method: GET
Request URL:...

Django Version: 1.11.6
Python Version: 3.5.2
Installed Applications:
['grappelli',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'django.contrib.postgres',
 'rest_framework',
 'rest_framework.authtoken',...
]
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Template error:
In template /home/ubuntu/venv/lib/python3.5/site-packages/grappelli/templates/admin/includes/fieldset.html, error at line 24
   <core.fields.PostalAddress object at 0x7f2c7fc085f8> is not JSON serializable   14 :                         {% if field.is_checkbox %}
   15 :                             <div class="c-1">&nbsp;</div>
   16 :                             <div class="c-2">
   17 :                                 {{ field.field }}{{ field.label_tag|prettylabel }}
   18 :                         {% else %}
   19 :                             <div class="c-1">{{ field.label_tag|prettylabel }}</div>
   20 :                             <div class="c-2">
   21 :                                 {% if field.is_readonly %}
   22 :                                     <div class="grp-readonly">{{ field.contents }}</div>
   23 :                                 {% else %}
   24 :                                      {{ field.field }} 
   25 :                                 {% endif %}
   26 :                         {% endif %}
   27 :                             {% if line.fields|length_is:'1' %}{{ line.errors }}{% endif %}
   28 :                             {% if not line.fields|length_is:'1' and not field.is_readonly %}{{ field.field.errors }}{% endif %}
   29 :                             {% if field.field.help_text %}
   30 :                                 <p class="grp-help">{{ field.field.help_text|safe }}</p>
   31 :                             {% endif %}
   32 :                         </div>
   33 :                     </div>
   34 :                 {% endfor %}


Traceback:

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/core/handlers/exception.py" in inner
  41.             response = get_response(request)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/core/handlers/base.py" in _get_response
  217.                 response = self.process_exception_by_middleware(e, request)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/core/handlers/base.py" in _get_response
  215.                 response = response.render()

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/response.py" in render
  107.             self.content = self.rendered_content

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/response.py" in rendered_content
  84.         content = template.render(context, self._request)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/backends/django.py" in render
  66.             return self.template.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  207.                     return self._render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/loader_tags.py" in render
  177.             return compiled_parent._render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/loader_tags.py" in render
  177.             return compiled_parent._render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/loader_tags.py" in render
  72.                 result = block.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/loader_tags.py" in render
  72.                 result = block.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  216.                     nodelist.append(node.render_annotated(context))

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/loader_tags.py" in render
  216.                 return template.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  209.                 return self._render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in _render
  199.         return self.nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  411.         return strip_spaces_between_tags(self.nodelist.render(context).strip())

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  216.                     nodelist.append(node.render_annotated(context))

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  216.                     nodelist.append(node.render_annotated(context))

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  322.                 return nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/defaulttags.py" in render
  322.                 return nodelist.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  990.                 bit = node.render_annotated(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_annotated
  957.             return self.render(context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render
  1046.         return render_value_in_context(output, context)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/template/base.py" in render_value_in_context
  1024.     value = force_text(value)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/utils/encoding.py" in force_text
  76.                     s = six.text_type(s)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/utils/html.py" in <lambda>
  385.         klass.__str__ = lambda self: mark_safe(klass_str(self))

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/forms/boundfield.py" in __str__
  40.             return self.as_widget() + self.as_hidden(only_initial=True)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/forms/boundfield.py" in as_widget
  125.             value=self.value(),

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/forms/boundfield.py" in value
  162.         return self.field.prepare_value(data)

File "/home/ubuntu/venv/lib/python3.5/site-packages/django/contrib/postgres/forms/jsonb.py" in prepare_value
  55.         return json.dumps(value)

File "/usr/lib/python3.5/json/__init__.py" in dumps
  230.         return _default_encoder.encode(obj)

File "/usr/lib/python3.5/json/encoder.py" in encode
  198.         chunks = self.iterencode(o, _one_shot=True)

File "/usr/lib/python3.5/json/encoder.py" in iterencode
  256.         return _iterencode(o, 0)

File "/usr/lib/python3.5/json/encoder.py" in default
  179.         raise TypeError(repr(o) + " is not JSON serializable")

Exception Type: TypeError at /admin/...
Exception Value: <core.fields.PostalAddress object at 0x7f2c7fc085f8> is not JSON serializable

Answer 1

您遇到的问题是 Django 使用它的 JSONField form field尝试反序列化管理员中的对象 - 这失败了，因为它仅使用 json.dumps() 无法处理您的 PostalAddress 对象。

您已经覆盖了 model 字段，但您还需要覆盖管理中使用的 form 字段。该文档描述了如何 specify a custom form field for a model field .

像这样:

from django.contrib.postgres.forms import JSONField 

# Define a new form field
class PostalAddressJSONField(JSONField):

    def prepare_value(self, value):
        # Here, deserialize the object in a way that works.
        # I've copied what you've done in your model field.
        return json.dumps(value.__dict__)

然后在您的 PostalAddressField 中指定这个新的表单字段:

class PostalAddressField(JSONField):

    def formfield(self, **kwargs):
        defaults = {'form_class': PostalAddressJSONField}
        defaults.update(kwargs)
        return super().formfield(**defaults)

ModelAdmin 表单现在应该使用这个自定义表单字段，并且能够正确反序列化它。