MongoDB-pymongo.errors.CursorN

Python, python3.

First get all the data from the database db ['test']. Find ({}, {_ id:0}), and then for the results

Demos = db ['demo'] .find ({}, {"_ id": 0}) for cursor in demos: do_something ()

However, when the do_something function takes too long and does not operate on the cursor for a long time, cursor times out on the mongodb server.

Solution

1. Set no_cursor_timeout = True. Never time out. The cursor connection will not be closed actively and needs to be closed manually.

Demos = db ['demo'] .find ({}, {"_ id": 0}, no_cursor_timeout = True) for cursor in demos: do_something () demo.close () # close the cursor

2. Set the number of documents returned by batch_size. By default, it should be 20 documents (I can't remember 233333). You can set it smaller.

# return only one document at a time

Demos = db ['demo']. Find ({}, {"_ id": 0}) .batch_size (1) for cursor in demos: do_something ()

Note: this method may still occur for more than 10 minutes and still does not return, such as you do some very time-consuming operations in do_something, depending on the actual situation.

Additional knowledge points:

Mongodb conditional operators, "$lt", "$lte", "$gt", "$gte", "$ne" are all comparison operators

Corresponds to "=", "! =".

Atomic operators: "$and", "$or", "$nor".

[2]:

Db.runCommand (

{

Distinct: "sofang_xinfang", key: "city"

}

)-distinct finds out how many city fields there are?