App Engine将项目附加到ListProperty

I think I'm loosing my mind, why doens't the following work?

我想我已经失去了理智,为什么不做以下工作呢?

class Parent(db.Model):
    childrenKeys = db.ListProperty(str,indexed=False,default=None)

p = Parent.get_or_insert(key_name='somekey')
p.childrenKeys = p.childrenKeys.append('newchildkey')
p.put()

I get this error:

我收到此错误:

BadValueError: Property childrenKeys is required

The doc says:

医生说:

default is the default value for the list property. If None, the default is an empty list. A list property can define a custom validator to disallow the empty list.

default是list属性的默认值。如果为None,则默认为空列表。 list属性可以定义自定义验证器以禁止空列表。

So the way I see it, I'm getting the default (an empty list) and appending a new value to it and the saving it.

所以我看到它的方式,我得到默认值(一个空列表)并为其添加一个新值并保存它。

2 个解决方案

#1

You should remove the p.childrenKeys assignment:

您应该删除p.childrenKeys分配:

class Parent(db.Model):
    childrenKeys = db.ListProperty(str,indexed=False,default=[])

p = Parent.get_or_insert('somekey')
p.childrenKeys.append('newchkey')
p.put()

#2

Replace this:

p.childrenKeys = p.childrenKeys.append('newchildkey')

with this:

p.childrenKeys.append('newchildkey')

append() returns None, which can't be assigned to p.childrenKeys.

append()返回None,无法分配给p.childrenKeys。

#1