代码之家 › 专栏 › 技术社区 › voscausa

appengine python NDB排序顺序没有影响

webapp2 app-engine-ndb google-app-engine python-2.7

voscausa · 技术社区 · 7 年前

我尝试在model.py中使用此类模型获取最后修改的条目:

class Example(ndb.Model):
    ....
    modified = ndb.DateTimeProperty(auto_now=True)
    created = ndb.DateTimeProperty(auto_now_add=True)

查询代码:

for each in ['Example', '...'] 
    model_class = webapp2.import_string('model.%s' % each)
    q = model_class.query()
    q.order(-model_class.modified)
    last_modified_entity = q.get()  # does not sort the entities

我还尝试了:

for each in ['Example', '...'] 
    model_class = webapp2.import_string('model.%s' % each)
    q = model_class.query()
    sort_prop = ndb.GenericProperty('modified')
    q.order(-sort_prop)
    last_modified_entity = q.get()  # does not sort the entities

1 回复 | 直到 7 年前

Dan Cornilescu 7 年前

使命感 .order() 在查询对象上,不会更改查询对象。它返回一个具有该顺序的新查询对象,但不改变原始查询对象。从…起 NDB Queries

而不是在单个表达式中指定整个查询过滤器, 您可能会发现,分步骤进行构建更为方便:例如:
query1 = Account.query()  # Retrieve all Account entitites
query2 = query1.filter(Account.userid >= 40)  # Filter on userid >= 40
query3 = query2.filter(Account.userid < 50)  # Filter on userid < 50 too
query3 query 上一个变量实例 ,所以施工 query2 query1 以及施工属于 查询3 不影响 问题1 或 查询2

>>>> from models.notification import Notification
>>>> query = Notification.query()
>>>> query
Query(kind='Notification')
>>>>
>>>> # this returns a new ordered query
>>>> query.order(Notification.created_on)
Query(kind='Notification', orders=...)
>>>> 
>>>> # but it does not alter the original query
>>>> query
Query(kind='Notification')
>>>>
>>>> # this is how you get the ordered query in a variable
>>>> ordered_query = query.order(Notification.created_on)
>>>> ordered_query
Query(kind='Notification', orders=...)
>>>> query
Query(kind='Notification')

因此,请将您的代码改为使用此代码:

q = q.order(-sort_prop)