如何使用bulkuploader 用 db.SelfReferenceProperty 填充类？

Question

我有一个类使用 db.SelfReferenceProperty 来创建树状结构。

尝试使用 appcfg.py upload_data --config_file=bulkloader.yaml --kind=Group --filename=group.csv (...) 填充数据库时 ，我收到一个异常，提示 BadValueError：名称不能为空。 ^{（下面是完整堆栈）}

我尝试对数据进行排序，以确保具有指向它们的外键的组位于第一个。那行不通。

通过从bulkloader.yaml中注释进行转换的行“import_transform：transform.create_foreign_key(‘Group’)”，数据被上传，但它将该属性存储为字符串，破坏了我的应用程序逻辑。

- kind: Group
  connector: csv
  connector_options:
  property_map:
    - property: __key__
      external_name: key
      export_transform: transform.key_id_or_name_as_string

    - property: name
      external_name: name
      # Type: String Stats: 9 properties of this type in this kind.

    - property: section
      external_name: section
      # Type: Key Stats: 6 properties of this type in this kind.
      import_transform: transform.create_foreign_key('Group')
      export_transform: transform.key_id_or_name_as_string

有没有什么方法可以使批量加载器考虑自引用，或者我应该对批量加载的数据进行服务器端转换或实现我自己的批量加载算法？

----
Traceback (most recent call last):
  File "/home/username/src/google_appengine/google/appengine/tools/adaptive_thread_pool.py", line 150, in WorkOnItems
    status, instruction = item.PerformWork(self.__thread_pool)
  File "/home/username/src/google_appengine/google/appengine/tools/bulkloader.py", line 691, in PerformWork
    transfer_time = self._TransferItem(thread_pool)
  File "/home/username/src/google_appengine/google/appengine/tools/bulkloader.py", line 846, in _TransferItem
    self.content = self.request_manager.EncodeContent(self.rows)
  File "/home/username/src/google_appengine/google/appengine/tools/bulkloader.py", line 1267, in EncodeContent
    entity = loader.create_entity(values, key_name=key, parent=parent)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/bulkloader_config.py", line 382, in create_entity
    return self.dict_to_entity(input_dict, self.bulkload_state)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/bulkloader_config.py", line 133, in dict_to_entity
    self.__run_import_transforms(input_dict, instance, bulkload_state_copy)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/bulkloader_config.py", line 230, in __run_import_transforms
    value = self.__dict_to_prop(transform, input_dict, bulkload_state)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/bulkloader_config.py", line 188, in __dict_to_prop
    value = transform.import_transform(value)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/bulkloader_parser.py", line 93, in __call__
    return self.method(*args, **kwargs)
  File "/home/username/src/google_appengine/google/appengine/ext/bulkload/transform.py", line 114, in generate_foreign_key_lambda
        return datastore.Key.from_path(kind, value)
  File "/home/username/src/google_appengine/google/appengine/api/datastore_types.py", line 384, in from_path
    ValidateString(id_or_name, 'name')
  File "/home/username/src/google_appengine/google/appengine/api/datastore_types.py", line 109, in ValidateString
    raise exception('%s must not be empty.' % name)
BadValueError: name must not be empty.

Answer 1

使用对类似问题的回答作为基地，我可以通过创建一个小 helpers.py 文件来成功解决这个问题，作为 transform.create_foreign_key 的包装：

from google.appengine.api import datastore

def create_foreign_key(kind, key_is_id=False):
  def generate_foreign_key_lambda(value):
    if value is None:
      return None

    if key_is_id:
      value = int(value)
    try:
      return datastore.Key.from_path(kind, value)
    except:
      return None

  return generate_foreign_key_lambda

一旦该文件位于同一目录中作为您的 yaml 批量上传配置文件 (bulkloader.yaml)，您可以将其添加到该文件中：

python_preamble:
- (...)
- import: helpers

transformers:

- kind: Group
  connector: csv
  connector_options:
  property_map:
    - property: __key__
      external_name: key
      export_transform: transform.key_id_or_name_as_string

    - property: name
      external_name: name

    - property: section
      external_name: section
      import_transform: helpers.create_foreign_key('Group')
                      # ^^^^^^^ we use the wrapper instead
      export_transform: transform.key_id_or_name_as_string

通过这些更改，批量上传现在可以正常工作了。

在使用这个之前，你一定要修改catch all except ，并将其替换为may be except BadValueError 。

Answer 2

transform.py （也许只是最近）包含一个解决此问题的装饰器：

def none_if_empty(fn):
  """A decorator which returns None if its input is empty else fn(x).

  Useful on import.  Can be used in config files
  (e.g. "transform.none_if_empty(int)" or as a decorator.

  Args:
    fn: Single argument transform function.

  Returns:
    Wrapped function.
  """

  def wrapper(value):


    if value == '' or value is None or value == []:
      return None
    return fn(value)

  return wrapper

因此使用以下内容也可以解决该问题，而无需引入自定义 helpers.py 文件:

transform.none_if_empty(transform.create_foreign_key('Group'))