Question

为什么游标不会迭代？我确信应该是一个简单的解决方案。

我尝试了多个Stack Overflow答案和Mongodb的文档 https://docs.mongodb.com/getting-started/python/query/

代码如下：

from pymongo import MongoClient

#Connect to Mongo Client 
client = MongoClient('mongodb://the_username:the_password@ds047124.mlab.com:47124/politicians_from_theage')
db = client.politicians_from_theage #define database used

# Define Collection
collection = db.posts
print collection

结果：

Collection(Database(MongoClient(host=['ds047124.mlab.com:47124'], document_class=dict, tz_aware=False, connect=True), u'politicians_from_theage'), u'posts')

然后光标将打印其位置：

# Define Cursor
my_cursor = collection.find()
print my_cursor

结果：

<pymongo.cursor.Cursor object at 0x0000000003247518>

然后尝试迭代游标提供超时：

 # Perform query 
    cursor = db.posts.find()
    #Iterate the cursor and print the documents.
for document in cursor:
    print(document)  #No Luck

跟踪错误或迭代：

Traceback (most recent call last):
  File "C:\PythonC\PythonWebScraping\17_MongoInterface\mongoget.py", line 18, in <module>
    for result_object in my_cursor:
  File "C:\Python27\lib\site-packages\pymongo\cursor.py", line 1090, in next
    if len(self.__data) or self._refresh():
  File "C:\Python27\lib\site-packages\pymongo\cursor.py", line 1012, in _refresh
    self.__read_concern))
  File "C:\Python27\lib\site-packages\pymongo\cursor.py", line 850, in __send_message
    **kwargs)
  File "C:\Python27\lib\site-packages\pymongo\mongo_client.py", line 827, in _send_message_with_response
    server = topology.select_server(selector)
  File "C:\Python27\lib\site-packages\pymongo\topology.py", line 210, in select_server
    address))
  File "C:\Python27\lib\site-packages\pymongo\topology.py", line 186, in select_servers
    self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: ds047124.mlab.com:47124: timed out

我试过迭代'cursor'，'my_cursor'和'collection'，每个都提供服务器超时的回溯错误。任何帮助/见解将不胜感激

Answer 1

这可能会对您有所帮助： -

 # Perform query 
cursor = db.posts.find().toAray(function(err, result){
     #Iterate the cursor and print the documents.
     for document in result:
     print(document);
}) //Will give you array of objects.

让我知道它是否有效。

Answer 2

找到答案，我专注于光标而不是将光标中的对象从JSON加载到JSON列表。

最终代码如下（删除URI）

import json
from datetime import date, timedelta
from pymongo import MongoClient
from bson import json_util

#Connect to Mongo Client 
client = MongoClient('mongodb://user:pword@ds047124.mlab.com:47124/politicians_from_theage')
db = client.politicians_from_theage #define database used
print db
# Define Collection
collection = db.posts
print collection # print Collection(Database(MongoClient(host=['ds047124.mlab.com:47124']...


cursor = collection.find()
print cursor

# Obtain json 
json_docs = []
for doc in cursor:
    json_doc = json.dumps(doc, default=json_util.default)
    json_docs.append(json_doc)
print json_docs #json result

# List Comprehension version
#json_docs = [json.dumps(doc, default=json_util.default) for doc in cursor]

#To get back from json again as string list
docs = [json.loads(j_doc, object_hook=json_util.object_hook) for j_doc in json_docs]
print docs

print 'kitty terminates program'

Answer 3

尝试一下：

cursor = db.posts.find()
for document in list(cursor):
    print(document)

从MLab迭代一个pymongo光标

3 个答案: