GAE NBD 实体在从 Python 中删除并刷新 Memchach 后仍可在数据存储查看器中看到

Question

下面是一个最小的Python示例，显示向 NDB 添加 个实体，然后删除全部。

然而，虽然实体似乎已被删除，但 Datastore Viewer 仍然显示它们 - 即使在我刷新后 Memcache.

我应该更改什么以便删除 NDB 实体？

我的代码：

from google.appengine.ext import ndb
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app

from models import Data

KEY = "fastsimon"
datum_key = dict()

class InvalidHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Invalid entry')

class GetHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Get!\n')
        name = self.request.get('name')
        out_str = "Should not be seen"
        try:
            ancestor_key = datum_key[name]
            qry = Data.owner_query(ancestor_key)
            data = qry.fetch()
            out_str = data[-1].value
        except KeyError:
            out_str = "None"
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write(out_str)

class EndHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('End!')
        qry = Data.query().iter(keys_only=True)
        print "before delete"
        list_of_keys = list()
        for q in qry:
            print "ndb.Key('Datum',q):",ndb.Key('Datum',q.integer_id())
            list_of_keys.append(ndb.Key('Datum',q.integer_id()))
        print "list_of_keys:",list_of_keys
        ndb.delete_multi(list_of_keys)
        print "after delete"
        for q in qry:
            print "ndb.Key('Datum',q):",ndb.Key('Datum',q.integer_id())

class SetHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Set!\n')
        name=self.request.get('name')
        data = Data(parent=ndb.Key("Datum", KEY),
                    name=name,
                    value=self.request.get('value'))
        print "data:",data
        ret_key = data.put()
        datum_key[name] = ret_key

def main():
    application = webapp.WSGIApplication([
            ('/get', GetHandler),
            ('/set', SetHandler),
            ('/end', EndHandler)],     
            debug=False) 
    global app
    app = application
    run_wsgi_app(app)

if __name__ == 'main':
    main()

models.py:

from google.appengine.ext import ndb

class Data(ndb.Model):
    name = ndb.StringProperty() # Upto 500 characters
    value = ndb.TextProperty(required=True) # Unlimited length

    @classmethod
    def owner_query(cls, parent_key):
        return cls.query(ancestor=parent_key).order(cls.name)

我采取的步骤：

已清除数据存储：

在浏览器中执行了以下操作：
http://localhost:8080/set?name=a&value=1
http://localhost:8080/set?name=b&value=2
http://localhost:8080/end

调试行是：

data: Data(key=Key('Datum', 'fastsimon', 'Data', None), name=u'a', value=u'1')
INFO     2016-10-20 11:29:34,213 module.py:788] default: "GET /set?name=a&value=1 HTTP/1.1" 200 5
data: Data(key=Key('Datum', 'fastsimon', 'Data', None), name=u'b', value=u'2')
INFO     2016-10-20 11:29:50,442 module.py:788] default: "GET /set?name=b&value=2 HTTP/1.1" 200 5
before delete
ndb.Key('Datum',q): Key('Datum', 4661104668049408)
ndb.Key('Datum',q): Key('Datum', 5787004574892032)
list_of_keys: [Key('Datum', 4661104668049408), Key('Datum', 5787004574892032)]
after delete
INFO     2016-10-20 11:30:04,125 module.py:788] default: "GET /end HTTP/1.1" 200 4

但是，当我转到 Datastore 查看器并按下 Flush Memcache 时，我仍然在那里看到实体：

我应该更改什么以便删除 NDB 实体？

Answer 1

一般来说，当您为您的实体使用祖先时，您需要小心您的查询 - 指定和不指定祖先键的查询将产生不同的（非重叠）结果。参见 Ancestor Queries

你的问题的根本原因是你在要删除的 list_of_keys 中构建的键与原始键不匹配，如果相应的实体有祖先，那么传递给 ndb.delete_multi 可能会遗漏一些您打算删除的密钥。

ndb.Key('Datum',q.integer_id()) 为没有祖先的实体 生成一个键，如果 q 是具有祖先的实体。

一个简单的解决方案是不转换要删除的密钥，而是将它们直接传递给 ndb.delete_multi()，例如，您可以简单地执行 ndb.delete_multi([key for key in qry]) 而不是 ndb.delete_multi(list_of_keys)

Answer 2

根据@DanCornilescu 的优秀建议，我更改了 EndHandler 的代码，它现在像冠军一样删除实体。

代码：

from google.appengine.ext import ndb
from google.appengine.ext import webapp
from google.appengine.ext.webapp.util import run_wsgi_app

from models import Data

KEY = "fastsimon"
datum_key = dict()

class InvalidHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Invalid entry')

class GetHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Get!\n')
        name = self.request.get('name')
        out_str = "Should not be seen"
        try:
            ancestor_key = datum_key[name]
            qry = Data.owner_query(ancestor_key)
            data = qry.fetch()
            out_str = data[-1].value
        except KeyError:
            out_str = "None"
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write(out_str)


class EndHandler(webapp.RequestHandler):
    def show_entities(self):
        for q in datum_key.values():
            k = ndb.Key('Datum', 'fastsimon', 'Data',q.integer_id())
            print "entity for",k,"=>", ndb.Key('Datum', 'fastsimon', 'Data',q.integer_id()).get()

    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('End!')
        print "datum_key.values():",datum_key.values()
        print "before delete"
        self.show_entities()
        ndb.delete_multi(datum_key.values())
        print "after delete"
        self.show_entities()


class SetHandler(webapp.RequestHandler):
    def get(self):
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.out.write('Set!\n')
        name=self.request.get('name')
        data = Data(parent=ndb.Key("Datum", KEY),
                    name=name,
                    value=self.request.get('value'))
        ret_key = data.put()
        datum_key[name] = ret_key
        print "data:",data

def main():
    application = webapp.WSGIApplication([
            ('/get', GetHandler),
            ('/set', SetHandler),
            ('/end', EndHandler)],     
            debug=False) 
    global app
    app = application
    run_wsgi_app(app)

if __name__ == 'main':
    main()

调试行：

data: Data(key=Key('Datum', 'fastsimon', 'Data', 4943129400573952), name=u'z', value=u'55')
INFO     2016-10-20 13:40:17,008 module.py:788] default: "GET /set?name=z&value=55 HTTP/1.1" 200 5
data: Data(key=Key('Datum', 'fastsimon', 'Data', 6069029307416576), name=u'x', value=u'88')
INFO     2016-10-20 13:40:28,556 module.py:788] default: "GET /set?name=x&value=88 HTTP/1.1" 200 5
datum_key.values(): [Key('Datum', 'fastsimon', 'Data', 4943129400573952), Key('Datum', 'fastsimon', 'Data', 6069029307416576)]
before delete
entity for Key('Datum', 'fastsimon', 'Data', 4943129400573952) => Data(key=Key('Datum', 'fastsimon', 'Data', 4943129400573952), name=u'z', value=u'55')
entity for Key('Datum', 'fastsimon', 'Data', 6069029307416576) => Data(key=Key('Datum', 'fastsimon', 'Data', 6069029307416576), name=u'x', value=u'88')
after delete
entity for Key('Datum', 'fastsimon', 'Data', 4943129400573952) => None
entity for Key('Datum', 'fastsimon', 'Data', 6069029307416576) => None
INFO     2016-10-20 13:40:40,517 module.py:788] default: "GET /end HTTP/1.1" 200 4

并且 Datastore 查看器不显示任何实体。

GAE NBD 实体在从 Python 中删除并刷新 Memchach 后仍可在数据存储查看器中看到

GAE NBD entities still seen in Datastore viewer after they are deleted from Python and Memchach is flushed

python

google-app-engine

app-engine-ndb

google-cloud-datastore