如何在python中限制mongo查询

Question

I am trying to retrieve data from mongodb with python. My db contains lots of data. So I want to limit the data while retrieving. I tried

import datetime
from pymongo import Connection
connection = Connection('localhost',27017)
db = connection['MyWork']


db_data = db.myusers.find().limit(2)
#db_data = db.myusers.find()[0:2]
print db_data
print db_data.count()
print db_data[0]
print db_data[1]
print db_data[2]

But I am getting more than two documents when I tried above. I am using pymongo driver. How to limit the values

<pymongo.cursor.Cursor object at 0x000000000267D518>
3
{u'age': 24.0, u'_id': ObjectId('552b6e90aad3e2d909d5fb28'), u'place': u'Ravipadu', u'name': u'Shiva'}
{u'age': 28.0, u'_id': ObjectId('552b6eabaad3e2d909d5fb29'), u'place': u'Rajahmundry', u'name': u'Anil'}
{u'age': 30.0, u'_id': ObjectId('552b6ec1aad3e2d909d5fb2a'), u'place': u'Manchili', u'name': u'Kishore'}

Answer 1

As specified in this question , indexed access will ignore the limit . And count() does not obey limit or skip by default as explained the manual . You can pass with_limit_and_skip=True to make count() work with limit.

print db_data.count(with_limit_and_skip=True)

Or you can iterate the cursor to see limit in effect.

for data in db.myusers.find().limit(2):
    print data

Answer 2

db.myusers.find(limit=2)

如果要应用某些条件，可以使用db.myusers.find({query}, limit=2)并计算结果数，请使用db.myusers.find({query}, limit=2).count()