如何摆脱 _BaseValue

Question

我正在使用我自己的 ndb 属性子类，因此我可以向它们添加我自己的属性。 当我检索存储在 ndb 中的数据时，我经常（并非总是）检索 _BaseValue 包装器中的数据。如何避免返回 _BaseValues？
目前，当我想使用数据时，我必须先将其传递给函数以获取 b_val。

请求参数

INFO     2013-02-01 08:15:05,834 debug.py:24] discount_application          
INFO     2013-02-01 08:15:05,835 debug.py:24] url_name                      10
INFO     2013-02-01 08:15:05,835 debug.py:24] name                          10%
INFO     2013-02-01 08:15:05,835 debug.py:24] discount.amount               10
INFO     2013-02-01 08:15:05,835 debug.py:24] discount_type                 discount
INFO     2013-02-01 08:15:05,836 debug.py:24] free_text_discount            
INFO     2013-02-01 08:15:05,836 debug.py:24] discount.currency             euro

使用自定义函数从数据存储接收到的数据

created                       _BaseValue(datetime.datetime(2013, 1, 31, 10, 41, 6, 757020))
updated                       _BaseValue(datetime.datetime(2013, 2, 1, 8, 13, 34, 924218))
name                          _BaseValue('10%')
active                        _BaseValue(True)
name_lower                    _BaseValue('10%')
url_name                      _BaseValue('10_')
discount_type                 _BaseValue('free_text_discount')
discount                      _BaseValue(Discount(amount=0, currency=u'euro'))
free_text_discount            _BaseValue('Krijg nu 10% korting')
discount_application          _BaseValue(' ')

解析请求参数后的数据

created                       2013-01-31 10:41:06.757020
updated                       2013-02-01 08:13:34.924218
name                          u'10%'
active                        True
name_lower                    u'10%'
url_name                      u'10_'
discount_type                 u'discount'
discount                      Discount(amount=1000, currency=u'euro')
free_text_discount            u''
discount_application          u' '

据我所知，数据的存储方式是我想要的还是非随机的。 放样后收到相同实例后的数据如下图所示。放样后的数据也显示为 discount.discount.amount 和 discount.discount.currency，而不仅仅是 discount.amount 和 discount.currency

created                       _BaseValue(datetime.datetime(2013, 1, 16, 14, 29, 52, 457230))
updated                       _BaseValue(datetime.datetime(2013, 2, 1, 8, 14, 29, 329138))
name                          _BaseValue('20%')
active                        _BaseValue(True)
name_lower                    _BaseValue('20%')
url_name                      u'20_'
discount_type                 _BaseValue('discount')
discount                      _BaseValue(Discount(discount=Expando(amount=2000L, currency='percent')))
free_text_discount            _BaseValue(' ')
discount_application          _BaseValue('')

动作看起来像这样

# BaseModel has some default properties and inherits from CleanModel
class Action(BaseModel):
    _verbose_name = _("Action")
    max_create_gid = gid.ADMIN
    max_list_gid = gid.ADMIN
    max_delete_gid = gid.ADMIN

    # And some additional irrelevant properties
    # properties is a module containing custom properties,
    # which have some additional properties and functions
    discount = properties.StructuredProperty(Discount,
            html_input_type="small_structure",
            verbose_name=_("Discount"),
            help_message=_("Set a minimum discount of 10%% or € 1,00"),
            max_edit_gid=gid.ADMIN)

    def validate(self, original=None):
        return {}

折扣看起来像这样

# CleanModel has some irrelevant functions and inherits from ndb.Model
class Discount(common_models.CleanModel):
    amount = EuroMoney.amount.update(
            verbose_name=_("Discount"))
    currency = EuroMoney.currency.update(
            choice_dict=cp_dict(EuroMoney.currency._choice_dict,
                                            updates={CURRENCY_PERCENT: "%%"}),
            max_edit_gid=gid.ADMIN)

Answer 1

_values 永远不应该被使用。应该使用 getattr。
一个循环遍历模型属性的示例：

entity = Model(**kwargs)
for name in entity._properties:
    val = getattr(entity, name)

Answer 2

不知道这里是否是这种情况，但我遇到了同样的问题，因为我正在制作实体属性的本地副本，编辑它们，然后将它们放回实体中（下面的示例）：

# I had wanted to store a list of strings, so I made this class
# (it was intended to store things like ["a", "b", "c"], etc.
class lists(ndb.Model):
        thisList = ndb.StringProperty(repeated=True)

def lets_go():
    with ndbclient.context():
        # Get the entity I want
        entity = ndb.Key(lists, "id").get()
        # Put it's existing data into a variable called 'local_list'
        local_list = entity.thisList
        # Append data to that variable
        local_list.append("d")
        # Assign the updated list back to the entity property
        entity.thisList = local_list 

这会给你一个像这样的列表：["_BaseValue('a')", "_BaseValue('b')"...] 而不是 ["a", "b"...]是问题所在。

如果我没记错的话，这实际上曾经在旧版本的 Google Cloud Datastore（大约 2018 年）中工作。但是，它现在给出了此处问题中提到的那种“_BaseValue”问题。这是我解决问题的方法——我直接编辑了 ndb 实体，没有制作列表的本地副本：

def lets_go():
    with ndbclient.context():
        # Get the entity I want
        entity = ndb.Key(lists, "id").get()
        # And append data to it directly
        entity.localList.append("d")
        

这会将一个实际的列表（如 ["a", "b"...]）放入实体中。