Google 数据存储 NDB 验证可选的 IntegerProperty

Question

如何验证空表单字段字符串 '' 以将 None 分配给 IntegerProperty？

class MyIntegerProperty(ndb.IntegerProperty):
    def _validate(self, value):
        if isinstance(value, basestring):
            if len(value) == 0 and self._required is False:
                return ?????????????????
            try:
                value = int(value)
            except ValueError:
                raise BadValueError(u'{0} must be a valid ' 
                    'integer'.format(self._name))
        if value < 0:
            raise BadValueError(u'{0} must be ' 
                'positive'.format(self._name))
        return value

class Account(ndb.Model):
    posint = MyIntegerProperty()

Docs say:

Things that _validate(), _to_base_type() and _from_base_type() do not need to handle:

None: They will not be called with None (and if they return None, this means that the value does not need conversion).

我目前正在做的是人工处理案件：

if len(request.form[name]) == 0:
    delattr(entity, name)
else:
    setattr(entity, name, request.form[name])

还能比这更聪明吗？

Answer 1

验证器可以生成属性值或引发异常，从而阻止实体被保存。来自 Property Options table:

Will be called with arguments (prop, value) and should either return the (possibly coerced) value or raise an exception. Calling the function again on a coerced value should not modify the value further. (For example, returning value.strip() or value.lower() is fine, but not value + '$'.) May also return None, which means "no change". See also Writing Property Subclasses

但是上面的none才是你真正想要的，就是删除属性。注意：

设置 None 的属性值（例如，对于 IntegerProperty 会失败）与删除属性不同（完全可以 IntegerProperty)
在使用验证器时设置属性值 None 可能会很棘手，因为从验证器返回 None 意味着 no change.

所以我相信你必须保持目前对这种情况的处理。

Google 数据存储 NDB 验证可选的 IntegerProperty

Google Datastore NDB validate optional IntegerProperty

google-app-engine

app-engine-ndb

google-cloud-datastore