要解决的问题
RESTful API对于批量操作存在一定的缺陷。例如资源的删除接口:
DELETE /api/resourse/<id>/
如果我们要删除100条数据怎么搞？难道要调用100次接口吗？
比较容易想到的是下面两种方案：
- 用逗号分割放进url里：
/api/resource/1,2,3... - 将需要删除的资源的id放到请求体里面
对于方案1，由于浏览器对url的长度存在限制，如果操作的资源过多就无法实现。
对于方案2，这种处理方式存在一定的风险，因为根据RPC标准文档，DELETE的请求体在语义上没有意义，一些网关、代理、防火墙在收到DELETE请求后，会把请求的body直接剥离掉。
所以我参考https://www.npmjs.com/package/restful-api，将批量处理的操作名称和数据全部放到请求体里，统一使用POST请求发送：
POST /api/resource/batch/
Body: {
"method": "create",
"data": [ { "name": "Mr.Bean" }, { "name": "Chaplin" }, { "name": "Jim Carrey" } ]
}
POST /api/resource/batch/
Body: {
"method": "update",
"data": { "1": { "name": "Mr.Bean" }, "2": { "name": "Chaplin" } }
}
POST /api/resource/batch/
Body: {
"method": "delete",
"data": [1, 2, 3]
}
Python实现
环境：python==3.6.5, django==2.2, djangorestframework==3.9.4
在GenericViewSet中加入了一些自定义的分发逻辑，将相应的Batch View放在Mixin里实现可重用。
class BatchGenericViewSet(GenericViewSet):
batch_method_names = ('create', 'update', 'delete')
def batch_method_not_allowed(self, request, *args, **kwargs):
method = request.batch_method
raise exceptions.MethodNotAllowed(method, detail=f'Batch Method {method.upper()} not allowed.')
def initialize_request(self, request, *args, **kwargs):
request = super().initialize_request(request, *args, **kwargs)
# 将batch_method从请求体中提取出来，方便后面使用
batch_method = request.data.get('method', None)
if batch_method is not None:
request.batch_method = batch_method.lower()
else:
request.batch_method = None
return request
def dispatch(self, request, *args, **kwargs):
self.args = args
self.kwargs = kwargs
request = self.initialize_request(request, *args, **kwargs)
self.request = request
self.headers = self.default_response_headers
try:
self.initial(request, *args, **kwargs)
# 首先识别batch_method并进行分发
if request.batch_method in self.batch_method_names:
method_name = 'batch_' + request.batch_method.lower()
handler = getattr(self, method_name, self.batch_method_not_allowed)
elif request.method.lower() in self.http_method_names:
handler = getattr(self, request.method.lower(), self.http_method_not_allowed)
else:
handler = self.http_method_not_allowed
response = handler(request, *args, **kwargs)
except Exception as exc:
response = self.handle_exception(exc)
self.response = self.finalize_response(request, response, *args, **kwargs)
return self.response
下面是Mixin，因为懒所以放在了一个里面：
class BatchMixin:
def batch_create(self, request, *args, **kwargs):
"""
Create a batch of model instance
request body like this:
{
"method": "create",
"data": [
{
"name": "Mr.Liu",
"age": 27
},
{
"name": "Chaplin",
"age": 88
}
]
}
"""
data = request.data.get('data', None)
if not isinstance(data, list):
raise exceptions.ValidationError({'data': 'Data must be a list.'})
serializer = self.get_serializer(data=data, many=True)
serializer.is_valid(raise_exception=True)
with transaction.atomic():
self.perform_create(serializer)
headers = self.get_success_headers(serializer.data)
return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)
def batch_update(self, request, *args, **kwargs):
"""
Update a batch of model instance
request body like this:
{
"method": "update",
"data": {
1: { "name": "Mr.Liu" },
2: { "name": "Jim Carrey" }
}
}
"""
data = request.data.get('data', None)
if not isinstance(data, dict):
raise exceptions.ValidationError({'data': 'Data must be a object.'})
ids = [int(id) for id in data]
queryset = self.get_queryset().filter(id__in=ids)
results = []
for obj in queryset:
serializer = self.get_serializer(obj, data=data[str(obj.id)], partial=True)
serializer.is_valid(raise_exception=True)
with transaction.atomic():
self.perform_update(serializer)
results.append(serializer.data)
return Response(results)
def batch_delete(self, request, *args, **kwargs):
"""
Delete a batch of model instance
request body like this:
{
"method": "delete",
"data": [1, 2]
}
"""
data = request.data.get('data', None)
if not isinstance(data, list):
raise exceptions.ValidationError({'data': 'Data must be a list.'})
queryset = self.get_queryset().filter(id__in=data)
with transaction.atomic():
self.perform_destroy(queryset)
return Response(status=status.HTTP_204_NO_CONTENT)
这样实现对于restframework框架的ModelPermission权限判定会出现问题，因为所有请求都是通过POST实现的，默认情况下无法对Model的增、删、改权限进行有效的判断。稍微修改下DjangoModelPermissions就可以了：
class BatchModelPermissions(DjangoModelPermissions):
batch_method_map = {
'create': 'POST',
'update': 'PATCH',
'delete': 'DELETE'
}
def has_permission(self, request, view):
if getattr(view, '_ignore_model_permissions', False):
return True
if not request.user or (
not request.user.is_authenticated and self.authenticated_users_only):
return False
queryset = self._queryset(view)
# 这里，这里
batch_method = getattr(request, 'batch_method', None)
if batch_method is not None:
perms = self.get_required_permissions(self.batch_method_map[batch_method], queryset.model)
else:
perms = self.get_required_permissions(request.method, queryset.model)
return request.user.has_perms(perms)
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