如何获取GAE Python NDB中的最新数据 [英] How to fetch the latest data in GAE Python NDB
问题描述
我正在使用GAE Python。我有两个根实体:
class X(ndb.Model):
subject = ndb.StringProperty()
grade = ndb.StringProperty()
class Y(ndb.Model):
identifier = ndb.StringProperty()
name = ndb.StringProperty()
school = ndb.StringProperty()
year = ndb.StringProperty()
result = ndb.StructuredProperty(X,repeated = True)
由于谷歌将数据存储在多个数据中心中,因此当我们执行查询时,我们可能无法获取最新数据(如果有一些更改已经 ):
def post(self):
identifier = self.request.get('identifier')
name = self.request.get('name')
school = self.request.get('school')
year = self.request.get('year')
qry = Y.query(ndb.AND(Y.name == name,Y.school == school,Y.year == year))
record_list = qry.fetch()
我的问题:我应该如何修改上面的获取操作,以获取最新的数据
我浏览了相关的 Google帮助文档,但无法理解如何在这里应用
基于Isaac答案的提示,以下是解决方案(latest_record_data是否包含实体的最新数据):
def post(self):
identifier = self.request.get('identifier')
name = self.request .get('name')
school = self.request.get('school')
year = self.request.get('year')
qry = Y.query(ndb .AND(Y.name == name,Y.school == school,Y.year == year))
record_list = qry.fetch()
record = record_list [0]
latest_record_data = record.key.get()
解决方案
在应用程序引擎中有几种方法可以获得强大的一致性,通常使用gets而不是查询并使用祖先查询。
要在你的例子中使用get,你可以将这个名字编码为实体键:
class Y(ndb.Model) :
result = ndb.StructuredProperty(X,repeated = True)
def put(name,result):
Y(key = ndb.Key(Y,name),结果).put()
def get_records(name):
record_list = ndb.Key(Y,name).get()
return record_list
祖先查询使用类似的概念来做更强大的事情。例如,获取具有特定名称的最新记录:
进口时间
class Y(ndb 。模型):
result = ndb.StructuredProperty(X,repeated = True)
@classmethod
def put_result(cls,name,result):
#Don对键中的最后一个字段不使用整数。 (一个奇怪的技巧)
key = ndb.Key('name',name,cls,str(int(time.time())))
cls(key = key,result = result)。 put()
@classmethod
def get_latest_result(cls,name):
qry = cls.query(ancestor = ndb.Key('name',name))。 (-cls.key)
latest = qry.fetch(1)
if latest:
return latest [0]
祖先是实体关键字的第一对。只要您至少可以将第一对关键字放入查询中,您就可以获得强大的一致性。
I am using GAE Python. I have two root entities:
class X(ndb.Model):
subject = ndb.StringProperty()
grade = ndb.StringProperty()
class Y(ndb.Model):
identifier = ndb.StringProperty()
name = ndb.StringProperty()
school = ndb.StringProperty()
year = ndb.StringProperty()
result = ndb.StructuredProperty(X, repeated=True)
Since google stores our data across several data centers, we might not get the most recent data when we do a query as shown below(in case some changes have been "put"):
def post(self):
identifier = self.request.get('identifier')
name = self.request.get('name')
school = self.request.get('school')
year = self.request.get('year')
qry = Y.query(ndb.AND(Y.name==name, Y.school==school, Y.year==year))
record_list = qry.fetch()
My question: How should I modify the above fetch operation to always get the latest data
I have gone through the related google help doc but could not understand how to apply that here
Based on hints from Isaac answer, Would the following be the solution(would "latest_record_data" contain the latest data of the entity):
def post(self):
identifier = self.request.get('identifier')
name = self.request.get('name')
school = self.request.get('school')
year = self.request.get('year')
qry = Y.query(ndb.AND(Y.name==name, Y.school==school, Y.year==year))
record_list = qry.fetch()
record = record_list[0]
latest_record_data = record.key.get()
解决方案 There's a couple ways on app engine to get strong consistency, most commonly using gets instead of queries and using ancestor queries.
To use a get in your example, you could encode the name into the entity key:
class Y(ndb.Model):
result = ndb.StructuredProperty(X, repeated=True)
def put(name, result):
Y(key=ndb.Key(Y, name), result).put()
def get_records(name):
record_list = ndb.Key(Y, name).get()
return record_list
An ancestor query uses similar concepts to do something more powerful. For example, fetching the latest record with a specific name:
import time
class Y(ndb.Model):
result = ndb.StructuredProperty(X, repeated=True)
@classmethod
def put_result(cls, name, result):
# Don't use integers for last field in key. (one weird trick)
key = ndb.Key('name', name, cls, str(int(time.time())))
cls(key=key, result=result).put()
@classmethod
def get_latest_result(cls, name):
qry = cls.query(ancestor=ndb.Key('name', name)).order(-cls.key)
latest = qry.fetch(1)
if latest:
return latest[0]
The "ancestor" is the first pair of the entity's key. As long as you can put a key with at least the first pair into the query, you'll get strong consistency.
这篇关于如何获取GAE Python NDB中的最新数据的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!