tl;dr: 这个解决方案提供了一个可完全重用的类，以最少的代码实现所需用例，如下面的示例使用情况所示。不要被外表吓到，它并不复杂。
经过一些尝试，我想出了以下解决方案，我相信这是非常令人满意的。我们将需要一个辅助函数和两个类，没有进一步的依赖关系。
HyperlinkedModelSerializer 的扩展
假设一个查询返回了一个Animal类的对象，而实际上它是一只Bird。那么get_actual将解析该Animal为Bird类的对象：
def get_actual(obj):
"""Expands `obj` to the actual object type.
"""
for name in dir(obj):
try:
attr = getattr(obj, name)
if isinstance(attr, obj.__class__):
return attr
except:
pass
return obj
ModelField 定义了一个字段，用于命名在序列化器中作为基础模型的模型名称：
class ModelField(serializers.ChoiceField):
"""Defines field that names the model that underlies a serializer.
"""
def __init__(self, *args, **kwargs):
super(ModelField, self).__init__(*args, allow_null=True, **kwargs)
def get_attribute(self, obj):
return get_actual(obj)
def to_representation(self, obj):
return obj.__class__.__name__
通过使用HyperlinkedModelHierarchySerializer，可以实现以下功能:
class HyperlinkedModelHierarchySerializer(serializers.HyperlinkedModelSerializer):
"""Extends the `HyperlinkedModelSerializer` to properly handle class hierearchies.
For an hypothetical model `BaseModel`, serializers from this
class are capable of also handling those models that are derived
from `BaseModel`.
The `Meta` class must whitelist the derived `models` to be
allowed. It also must declare the `model_dependent_fields`
attribute and those fields must also be added to its `fields`
attribute, for example:
wing = serializers.CharField(allow_null=True)
tail = serializers.CharField(allow_null=True)
class Meta:
model = Animal
models = (Bird, Dog)
model_dependent_fields = ('wing', 'tail')
fields = ('model', 'id', 'name') + model_dependent_fields
read_only_fields = ('id',)
The `model` field is defined by this class.
"""
model = ModelField(choices=[])
def __init__(self, *args, **kwargs):
"""Instantiates and filters fields.
Keeps all fields if this serializer is processing a CREATE
request. Retains only those fields that are independent of
the particular model implementation otherwise.
"""
super(HyperlinkedModelHierarchySerializer, self).__init__(*args, **kwargs)
self.Meta.models_by_name = {model.__name__: model for model in self.Meta.models}
self.Meta.model_names = self.Meta.models_by_name.keys()
self.fields['model'] = ModelField(choices=self.Meta.model_names, read_only=bool(self.instance))
def remove_missing_fields(obj):
unused_field_keys = set()
for field_key in self.Meta.model_dependent_fields:
if not hasattr(obj, field_key):
unused_field_keys |= {field_key}
for unused_field_key in unused_field_keys:
self.fields.pop(unused_field_key)
if not self.instance is None:
if not isinstance(self.instance, QuerySet):
self.instance = get_actual(self.instance)
remove_missing_fields(self.instance)
else:
for field_key in self.Meta.model_dependent_fields:
self.fields.pop(field_key)
def validate_model(self, value):
"""Validates the `model` field.
"""
if self.instance is None:
if value not in self.Meta.model_names:
raise serializers.ValidationError('Must be one of: ' + (', '.join(self.Meta.model_names)))
else:
return value
else:
return get_actual(self.instance).__class__.__name__
def create(self, validated_data):
"""Creates instance w.r.t. the value of the `model` field.
"""
model = self.Meta.models_by_name[validated_data.pop('model')]
for field_key in self.Meta.model_dependent_fields:
if not field_key in model._meta.get_all_field_names():
validated_data.pop(field_key)
self.fields.pop(field_key)
return model.objects.create(**validated_data)
使用示例
以下是我们如何使用它。在serializers.py中：
class AnimalSerializer(HyperlinkedModelHierarchySerializer):
wing = serializers.CharField(allow_null=True)
tail = serializers.CharField(allow_null=True)
class Meta:
model = Animal
models = (Bird, Dog)
model_dependent_fields = ('wing', 'tail')
fields = ('model', 'id', 'name') + model_dependent_fields
read_only_fields = ('id',)
在views.py中：
class AnimalViewSet(viewsets.ModelViewSet):
queryset = Animal.objects.all()
serializer_class = AnimalSerializer
Animal，我就不能像这样查询Animal.objects.all()，也不能将Dog.objects.all()和Bird.objects.all()合并起来，这会让处理Animal对象变得非常不方便。 - theV0ID