由于cursor（）方法中“ IN过滤器”的局限性，使用游标进行分页查询会导致错误……该怎么办？

小编典典

由于cursor（）方法中“ IN过滤器”的局限性，使用游标进行分页查询会导致错误……该怎么办？

python

我正在通过使用以下模型开发类似微博系统的Twitter：

class Member(db.Model):    
    user = db.UserProperty(required=True)
    follower_count = db.IntegerProperty(default=0) # members following you    
    following_count = db.IntegerProperty(default=0) # members you are following

class NewsItem(db.Model):    
    text = db.StringProperty(required=True)
    posted_by = db.ReferenceProperty(reference_class=Member,required=True,collection_name="posted_items")
    posted_on = db.DateTimeProperty(auto_now_add=True)
    status = db.IntegerProperty(default=1) # 0: deleted

class Follow(db.Model):    
    member = db.ReferenceProperty(reference_class=Member,required=True,collection_name="followings")    
    followed_member = db.ReferenceProperty(reference_class=Member,required=True,collection_name="followers")    
    added_on = db.DateTimeProperty(auto_now_add=True)

在此模型结构中，我使用以下代码检索当前用户遵循的成员的消息：

follow_log_list = Follow.gql('WHERE member = :1 ', member)
followed_member_list = []
for follow_log in follow_log_list:
    followed_member_list.append(follow_log.followed_member)

query = NewsItem.all()
query.filter('posted_by IN', followed_member_list)
query.filter('status =', 1)
query.order('-posted_on')
query.with_cursor(cursor)   
newsList = query.fetch(10)

template_values['cursor'] = query.cursor()

调用query.cursor（）方法时，出现以下错误：

“没有游标可用于MultiQuery（使用“ IN”或“！=“运算符进行查询）”

这是正常现象，因为在游标的文档中此限制明确表示为：

http://code.google.com/appengine/docs/python/datastore/queries.html

“不能在使用IN或！=过滤运算符的查询中使用游标。”

获取关注成员职位的替代方法是什么？

谢谢，

编辑：已发布消息按其状态过滤，并按其发布日期排序…但是示例未在此处显示，我已对其进行了更改…

阅读 192

2021-01-20

共1个答案

小编典典

我的解决方案是将日期值像光标一样使用，正如我描述的那样，它是对尼克森的答案的注释…就像这样：

if cursor: # This is not actually a cursor! It is base64 datetime string
  cursordate = _strptime(base64.b64decode(cursor)) # _strptime is a local method that converts str to datetime

# IN has a limit for lists: 30 items allowed
listofNewsLists = []
listofMemberLists = [followed_member_list[i:i+30] for i in range(0, len(followed_member_list), 30)]
for eachList in listofMemberLists:
   query = NewsItem.all()
   query.filter('posted_by IN', eachList).filter('status =', 1)
   if cursor:
      query.filter('posted_on <', cursordate)
   query.order('-posted_on')                        
   listofNewsLists.append(query.fetch(PAGE_SIZE))

  newsList = []
  if listofNewsLists:
    emptyListCount = 0
    while len(newsList) < PAGE_SIZE and emptyListCount < len(listofNewsLists):
      max = datetime.datetime.min
      maxInd = -1
      emptyListCount = 0
      for i in range(len(listofNewsLists)):
        if listofNewsLists[i] == []:
          emptyListCount += 1
        elif listofNewsLists[i][0].posted_on > max:
          max = listofNewsLists[i][0].posted_on
          maxInd = i
      if max > datetime.datetime.min:
        newsList.append(listofNewsLists[maxInd].pop(0))

template_values['cursor'] = base64.b64encode(newsList[-1].posted_on.isoformat())

那是; 我将最后显示的项目的日期值存储为新列表的起点…

除非我有具有相同post_on值的项目，否则这很好（我猜）。

2021-01-20