RESTful API批量操作的实现

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：

1. 用逗号分割放进url里：/api/resource/1,2,3...
2. 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：python3.6.5, django2.2, 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)

参考：https://www.npmjs.com/package/restful-api