我需要实现一个RESTful API，它关注Django的REST Framwork模型的继承。我认为this是构建API的简洁方法。基本思想是仅通过所呈现的属性集来区分对象类。但是如何用Django完成呢？让我们坚持一个简单的示例场景：
Animal具有属性age。Bird通过属性Animal扩展wing，例如它的大小。Dog通过属性Animal扩展tail，例如它的长度。示例性要求：
/animals/列出所有具有一般属性的动物，即年龄，就足够了。ID=1的动物是一只鸟，/animals/1应该给出类似的东西：的
{
'age': '3',
'class': 'Bird',
'wing': 'big'
}
ID=2的动物是狗，/animals/2应该给出类似的东西：的
{
'age': '8',
'class': 'Dog',
'tail': 'long'
}
我没有运气实现Django的REST框架，主要是因为我没有成功添加/删除特定于类的字段。特别是我想知道，如何在这种情况下实现创建操作？
答案 0 :(得分：3)
tl; dr： 它看起来并不复杂。此解决方案提出了一个完全可重用的类，它使用最少的代码实现所请求的用例，如下面的 示例用法 所示。
经过一番摆弄，我提出了以下解决方案，我相信，这是非常令人满意的。我们需要一个辅助函数和两个类，没有进一步的依赖。
var Client = new HttpClient();
var request = new HttpRequestMessage(
new HttpMethod("PATCH"),
String.Format("/drive/items/{0}", folderId)
);
var renameInstruction = new StringContent("{\"name\":\"NewFolder\"}");
request.Content = renameInstruction;
var opResult = await Client.SendAsync(request);
假设查询从HyperlinkedModelSerializer类返回了一个对象，实际上是Animal。比Bird会将get_actual解析为对象格式Animal类：
Bird 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
定义了一个字段，该字段命名了序列化程序基础的模型：
ModelField 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__
有神奇之处：
HyperlinkedModelHierarchySerializer这就是我们如何使用它。在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)
# complete the meta data
self.Meta.models_by_name = {model.__name__: model for model in self.Meta.models}
self.Meta.model_names = self.Meta.models_by_name.keys()
# update valid model choices,
# mark the model as writable if this is a CREATE request
self.fields['model'] = ModelField(choices=self.Meta.model_names, read_only=bool(self.instance))
def remove_missing_fields(obj):
# drop those fields model-dependent fields that `obj` misses
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:
# processing an UPDATE, LIST, RETRIEVE or DELETE request
if not isinstance(self.instance, QuerySet):
# this is an UPDATE, RETRIEVE or DELETE request,
# retain only those fields that are present on the processed instance
self.instance = get_actual(self.instance)
remove_missing_fields(self.instance)
else:
# this is a LIST request, retain only those fields
# that are independent of the particular model implementation
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:
# validate for CREATE
if value not in self.Meta.model_names:
raise serializers.ValidationError('Must be one of: ' + (', '.join(self.Meta.model_names)))
else:
return value
else:
# model cannot be changed
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)
：
serializers.py在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',)
：
views.py