我有以下内容：
target_content_type = models.ForeignKey(ContentType, related_name='target_content_type')
target_object_id = models.PositiveIntegerField()
target = generic.GenericForeignKey('target_content_type', 'target_object_id')
我希望 dumpdata --natural 为这种关系发出一个自然键。这可能吗？如果没有，是否有另一种策略不会将我与目标的主键联系起来？
TL;DR - 目前没有健全的方法这样做，除非创建一个自定义Serializer/Deserializer对。
具有通用关系的模型的问题在于 Django 根本不将target其视为一个字段，而只是target_content_typeand target_object_id，它会尝试单独对它们进行序列化和反序列化。
负责序列化和反序列化 Django 模型的类位于模块django.core.serializers.base和django.core.serializers.python. 所有其他（xml和json）yaml扩展它们中的任何一个（和python扩展base）。字段序列化是这样完成的（省略不相关的行）：
for obj in queryset:
for field in concrete_model._meta.local_fields:
if field.rel is None:
self.handle_field(obj, field)
else:
self.handle_fk_field(obj, field)
这是第一个复杂的问题：外键ContentType处理得很好，正如我们预期的那样使用自然键。但是由PositiveIntegerField处理handle_field，它是这样实现的：
def handle_field(self, obj, field):
value = field._get_val_from_obj(obj)
# Protected types (i.e., primitives like None, numbers, dates,
# and Decimals) are passed through as is. All other values are
# converted to string first.
if is_protected_type(value):
self._current[field.name] = value
else:
self._current[field.name] = field.value_to_string(obj)
即这里唯一的自定义可能性（子类化PositiveIntegerField和定义自定义value_to_string）将无效，因为序列化程序不会调用它。将数据类型更改为target_object_id整数以外的其他内容可能会破坏许多其他内容，因此这不是一个选项。
在这种情况下，我们可以定义我们的自定义handle_field来发出自然键，但随之而来的是第二个复杂性：反序列化是这样完成的：
for (field_name, field_value) in six.iteritems(d["fields"]):
field = Model._meta.get_field(field_name)
...
data[field.name] = field.to_python(field_value)
即使我们自定义了该方法，它也会在对象的上下文之外单独to_python起作用。field_value使用整数时这不是问题，因为无论它是什么模型，它都会被解释为模型的主键。target_content_type但是要反序列化一个自然键，首先我们需要知道该键属于哪个模型，并且除非我们获得对该对象的引用（并且该字段已经被反序列化），否则该信息不可用。
正如您所看到的，这不是一项不可能完成的任务——支持泛型关系中的自然键——但要实现这一点，需要在序列化和反序列化代码中进行很多更改。必要的步骤，然后（如果有人觉得可以完成任务）是：
Field扩展PositiveIntegerField，使用编码/解码对象的方法 - 调用引用的模型natural_key和get_by_natural_key；handle_field器以调用编码器（如果存在）；field_value而且传递对解码的引用ContentType。我编写了一个支持 GenericFK 的自定义序列化器和反序列化器。简单地检查了一下，它似乎完成了这项工作。
这就是我想出的：
import json
from django.contrib.contenttypes.generic import GenericForeignKey
from django.utils import six
from django.core.serializers.json import Serializer as JSONSerializer
from django.core.serializers.python import Deserializer as \
PythonDeserializer, _get_model
from django.core.serializers.base import DeserializationError
import sys
class Serializer(JSONSerializer):
def get_dump_object(self, obj):
dumped_object = super(CustomJSONSerializer, self).get_dump_object(obj)
if self.use_natural_keys and hasattr(obj, 'natural_key'):
dumped_object['pk'] = obj.natural_key()
# Check if there are any generic fk's in this obj
# and add a natural key to it which will be deserialized by a matching Deserializer.
for virtual_field in obj._meta.virtual_fields:
if type(virtual_field) == GenericForeignKey:
content_object = getattr(obj, virtual_field.name)
dumped_object['fields'][virtual_field.name + '_natural_key'] = content_object.natural_key()
return dumped_object
def Deserializer(stream_or_string, **options):
"""
Deserialize a stream or string of JSON data.
"""
if not isinstance(stream_or_string, (bytes, six.string_types)):
stream_or_string = stream_or_string.read()
if isinstance(stream_or_string, bytes):
stream_or_string = stream_or_string.decode('utf-8')
try:
objects = json.loads(stream_or_string)
for obj in objects:
Model = _get_model(obj['model'])
if isinstance(obj['pk'], (tuple, list)):
o = Model.objects.get_by_natural_key(*obj['pk'])
obj['pk'] = o.pk
# If has generic fk's, find the generic object by natural key, and set it's
# pk according to it.
for virtual_field in Model._meta.virtual_fields:
if type(virtual_field) == GenericForeignKey:
natural_key_field_name = virtual_field.name + '_natural_key'
if natural_key_field_name in obj['fields']:
content_type = getattr(o, virtual_field.ct_field)
content_object_by_natural_key = content_type.model_class().\
objects.get_by_natural_key(obj['fields'][natural_key_field_name][0])
obj['fields'][virtual_field.fk_field] = content_object_by_natural_key.pk
for obj in PythonDeserializer(objects, **options):
yield obj
except GeneratorExit:
raise
except Exception as e:
# Map to deserializer error
six.reraise(DeserializationError, DeserializationError(e), sys.exc_info()[2])
我更新了 Django 2.2 及更高版本的 OmriToptix答案。
在 Django 2.0 中：
Model._meta.virtual_fields 属性被移除。
所以，新的序列化器和反序列化器：
import json
from django.contrib.contenttypes.fields import GenericForeignKey
from django.utils import six
from django.core.serializers.json import Serializer as JSONSerializer
from django.core.serializers.python import Deserializer as \
PythonDeserializer, _get_model
from django.core.serializers.base import DeserializationError
import sys
class Serializer(JSONSerializer):
def get_dump_object(self, obj):
dumped_object = super(JSONSerializer, self).get_dump_object(obj)
if hasattr(obj, 'natural_key'):
dumped_object['pk'] = obj.natural_key()
for field in obj._meta.get_fields():
if type(field) == GenericForeignKey:
content_object = getattr(obj, field.name)
dumped_object['fields'][field.name + '_natural_key'] = content_object.natural_key()
return dumped_object
def Deserializer(stream_or_string, **options):
if not isinstance(stream_or_string, (bytes, six.string_types)):
stream_or_string = stream_or_string.read()
if isinstance(stream_or_string, bytes):
stream_or_string = stream_or_string.decode('utf-8')
try:
objects = json.loads(stream_or_string)
for obj in objects:
Model = _get_model(obj['model'])
if isinstance(obj['pk'], (tuple, list)):
o = Model.objects.get_by_natural_key(*obj['pk'])
obj['pk'] = o.pk
for field in Model._meta.get_fields():
if type(field) == GenericForeignKey:
natural_key_field_name = field.name + '_natural_key'
if natural_key_field_name in obj['fields']:
content_type = getattr(o, field.ct_field)
content_object_by_natural_key = content_type.model_class().\
objects.get_by_natural_key(*obj['fields'][natural_key_field_name])
obj['fields'][field.fk_field] = content_object_by_natural_key.pk
del obj['fields'][natural_key_field_name]
for obj in PythonDeserializer(objects, **options):
yield obj
except GeneratorExit:
raise
except Exception as e:
six.reraise(DeserializationError, DeserializationError(e), sys.exc_info()[2])
然后，在您的 settings.py 中，设置此配置：
SERIALIZATION_MODULES = {
"json": "path.to.serializer_file"
}
现在，您可以使用：
python3 manage.py dumpdata --natural-foreign --natural-primary > dump.json
其他方式，如果您需要转储一些数据（过滤查询集），您可以从代码中进行：
from path.to.serializers import Serializer, Deserializer
# Serialize
registers = YourModel.objects.filter(some_attribute=some_value)
dump = Serializer().serialize(registers, use_natural_foreign_keys=True, use_natural_primary_keys=True)
# Deserialize
for deserialized_object in Deserializer(dump, use_natural_foreign_keys=True, use_natural_primary_keys=True):
print(deserialized_object.object) # See here https://docs.djangoproject.com/en/2.2/topics/serialization/