CODEWITHSUNDEEP
pythonmongodbindexingpymongo
Stack Exchange User
Stack Exchange User

Reputation: 778

Best way to extract all _id from mongodb collection

What is best way to extract all _id from mongodb collection? I am using pymongo to work with mongodb. Following code:

for item in db.some_collection.find({}, {'_id': 1}):
    # do something

takes some time to iterate over all collection. I need only _id values and they all should fit in memory. Why does this code not complete immediately?

Upvotes: 4

Views: 1659

Answers (1)

Pavel Anossov
Pavel Anossov

Reputation: 62908

Use distinct:

some_collection.distinct('_id')

In [5]: c = pymongo.connection.Connection('127.0.0.1')

In [6]: c['test']['test'].insert({'a': 2})
Out[6]: ObjectId('5159c8e9d286da0efccb7b70')

In [7]: c['test']['test'].insert({'a': 3})
Out[7]: ObjectId('5159c8ecd286da0efccb7b71')

In [8]: c['test']['test'].insert({'a': 5})
Out[8]: ObjectId('5159c8edd286da0efccb7b72')

In [9]: c['test']['test'].distinct('_id')
Out[9]:
[ObjectId('5159c8e9d286da0efccb7b70'),
 ObjectId('5159c8ecd286da0efccb7b71'),
 ObjectId('5159c8edd286da0efccb7b72')]

Upvotes: 7

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