Pymongo：遍历集合中的所有文档 [英] Pymongo: iterate over all documents in the collection
问题描述
我正在使用PyMongo并尝试遍历MongoDB集合中的（一千万个）文档，并仅提取几个键：名称和地址，然后将它们输出到.csv文件。
I am using PyMongo and trying to iterate over (10 millions) documents in my MongoDB collection and just extract a couple of keys: "name" and "address", then output them to .csv file.
我无法找出使用find（）。forEach（）的正确语法
I cannot figure out the right syntax to do it with find().forEach()
我正在尝试类似
cursor = db.myCollection.find({"name": {$regex: REGEX}})
其中REGEX会匹配所有内容-并导致杀死。
我也尝试过
where REGEX would match everything - and it resulted in "Killed". I also tried
cursor = db.myCollection.find({"name": {"$exist": True}})
但这也不起作用。
有什么建议吗？
推荐答案
我找不到正确的语法来做到这一点与find（）。forEach（）
I cannot figure out the right syntax to do it with find().forEach()
cursor.forEach（）不适用于Python，它是一个JavaScript函数。您将必须获得一个游标并对其进行迭代。请参见 PyMongo教程：查询多个文档，您可以在其中进行操作：
cursor.forEach() is not available for Python, it's a JavaScript function. You would have to get a cursor and iterate over it. See PyMongo Tutorial: querying for more than one document, where you can do :
for document in myCollection.find():
print(document) # iterate the cursor
其中REGEX将匹配所有内容-并且它导致被杀。
where REGEX would match everything - and it resulted in "Killed".
不幸的是，这里缺少调试为什么的原因和信息的信息。虽然如果您想匹配所有内容，则只需声明：
Unfortunately there's lack of information here to debug on why and what 'Killed' is. Although if you would like to match everything, you can just state:
cursor = db.myCollection.find({"name": {$regex: /.*/}})
给出该字段名称包含字符串值。尽管使用 $ exists 检查字段 name 是否比使用正则表达式更可取。
Given that field name contains string values. Although using $exists to check whether field name exists would be preferable than using regex.
使用 $ exists 运算符不正确。您在 $ exists 中丢失了 s 。同样，不幸的是，我们对很多无效信息的了解并不多，这些信息无法帮助进一步调试。
While the use of $exists operator in your example above is incorrect. You're missing an s in $exists. Again, unfortunately we don't know much information on what 'didn't work' meant to help debug further.
如果您正在编写用于Python练习的脚本，我建议您查看一下：
If you're writing this script for Python exercise, I would recommend to review:
- PyMongo Tutorial
- MongoDB Tutorial: query documents
您还可以在 MongoDB大学 M101P：适用于Python开发人员的MongoDB的a> 。
You could also enrol in a free online course at MongoDB University for M101P: MongoDB for Python Developers.
但是，如果您只是想完成从集合中导出CSV的任务。另外，您也可以使用MongoDB的 mongoexport 。
However, if you are just trying to accomplish your task of exporting CSV from a collection. As an alternative you could just use MongoDB's mongoexport. Which has the support for :
- 通过-字段名称，地址
- 通过-键入 csv
- 通过 --query ...
- Exporting specific fields via --fields "name,address"
- Exporting in CSV via --type "csv"
- Exporting specific values with query via --query "..."
请参见 mongoexport用法以获取更多信息。
See mongoexport usage for more information.
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