我试图通过使用自定义验证器来简化ndb KeyProperties的JSON序列化和反序列化,该验证器将字符串转换为相应类型的Key
。
想法是拥有这样的属性:
def key_validator(kind):
def validator(prop, value):
if not isinstance(value, ndb.Key):
return ndb.Key(kind, value)
return value
return validator
class Bar(ndb.Model):
foo = ndb.KeyProperty('Foo', validator=key_validator('Foo'))
如您所见,验证器将任何字符串转换为给定类型的Key
。
目标是能够将包含密钥id的JSON对象传递给populate
方法,如下所示:
bar = Bar()
bar.populate(json.loads('{"foo": "1234"}'))
哪个应该有效地做到这一点:
bar = Bar()
bar.foo = ndb.Key("Foo", "1234")
问题是这需要覆盖KeyProperty
,因为在执行某些基本验证后调用验证器失败,因为"1234"
显然不是Key
,请参阅{{ 3}}
为了完成这项工作,我已经创建了一个" ValidationMixin"以及在进行任何其他验证之前调用验证器的新KeyProperty(并且还将Key
序列化为id)。
class ValidationMixin(object):
# make sure to call _validator before we do as the very first validation step
def _do_validate(self, value):
if self._validator is not None:
newvalue = self._validator(self, value)
if newvalue is not None:
value = newvalue
return super(ValidationMixin, self)._do_validate(value)
# A KeyProperty that allows a validator to generate a Key.
# In addition it serializes to just the id of the key
class KeyProperty(ValidationMixin, ndb.KeyProperty):
# return just the id of the key
def _get_for_dict(self, entity):
value = self._get_value(entity)
if self._repeated:
return [v.id() for v in value]
elif value is not None:
return value.id()
return value
使用此KeyProperty
就像非重复属性的魅力一样。不幸的是,对于具有repeated=True
的属性,它会失败。
当我致电bar.populate(json.loads('[{"foo": "1234"}]'))
后跟put()
:
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 3451, in _put
return self._put_async(**ctx_options).get_result()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 383, in get_result
self.check_success()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 427, in _help_tasklet_along
value = gen.throw(exc.__class__, exc, tb)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/context.py", line 824, in put
key = yield self._put_batcher.add(entity, options)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/tasklets.py", line 430, in _help_tasklet_along
value = gen.send(val)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/context.py", line 358, in _put_tasklet
keys = yield self._conn.async_put(options, datastore_entities)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 1852, in async_put
pbs = [entity_to_pb(entity) for entity in entities]
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 697, in entity_to_pb
pb = ent._to_pb()
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 3167, in _to_pb
prop._serialize(self, pb, projection=self._projection)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1422, in _serialize
values = self._get_base_value_unwrapped_as_list(entity)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1192, in _get_base_value_unwrapped_as_list
wrapped = self._get_base_value(entity)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1180, in _get_base_value
return self._apply_to_values(entity, self._opt_call_to_base_type)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1355, in _apply_to_values
newvalue = function(value)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1234, in _opt_call_to_base_type
value = _BaseValue(self._call_to_base_type(value))
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1255, in _call_to_base_type
return call(value)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 1331, in call
newvalue = method(self, value)
File "/base/data/home/runtimes/python27/python27_lib/versions/1/google/appengine/ext/ndb/model.py", line 2013, in _validate
raise datastore_errors.BadValueError('Expected Key, got %r' % (value,))
BadValueError: Expected Key, got [Key('Foo', '486944fe896a44c689275e6f19e3084a')]
正如您所看到的,它抱怨值是列表而不是单个Key
。请注意,put()
中的异常不在populate
中,因此_set_value
执行的初始验证成功。
所以我的问题是,我的方法是破碎还是应该有效?如果它应该工作,为什么它不起作用,如何解决?
根据堆栈跟踪,代码执行通过issue 268,这很奇怪,因为属性被重复,并且应该是model.py, line 1355中的另一个分支
我刚刚发现,当我从模型中删除未重复的KeyProperty
时,它会起作用。看起来序列化被破坏,错误的KeyProperty
实例被传递给_seralize
方法
答案 0 :(得分:1)
好的,找到了。 KeyProperty
有一个非常奇怪的构造函数“签名魔法”(model.py, line 1963)。
关键是如果第一个参数是一个字符串,它就成了属性的字段名,而不是那种!如果要按字符串指定种类,则必须使用关键字参数,否则kind参数必须是实际类型而不仅仅是名称。如果我错了,请纠正我,但这不是公开文件的一部分。这真的很令人困惑,因为使用ndb.Key
,您实际上可以将类型指定为字符串作为第一个位置参数。
实际上,我有3个KeyProperties具有相同的类型,但属性名称不同。但是,由于我将类型指定为字符串,它实际上成了名称。所以这三个属性都使用相同的名称。因此,重复的属性值使用非重复的KeyProperty
实例序列化,从而导致此崩溃。
解决方案是使用关键字参数指定种类:
foo = ndb.KeyProperty(kind='Foo', validator=key_validator('Foo'))
从/向JSON序列化KeyProperties现在运行良好。