How can I return an array of mongodb objects in pymongo (without a cursor)? Can MapReduce do this?

Question

I have a db set up in mongo that I\'m accessing with pymongo.

I\'d like to be able to pull a small set of fields into a list of dictionaries. So, something like wha

Answer 1

What you can do is to call mapReduce in pymongo and pass it the find query as an argument, it could be like this:

db.yourcollection.Map_reduce(map_function, reduce_function,query='{}')

About the projections I think that you would need to do them in the reduce function since query only specify the selection criteria as it says in the mongo documentation

Answer 2

You don't need to call mapReduce, you just turn the cursor into a list like so:

>>> data = list(col.find({},{"a":1,"b":1,"_id":0}).limit(2))
>>> data
[{u'a': 1.0, u'b': 2.0}, {u'a': 2.0, u'b': 3.0}]

where col is your db.collection object.

But caution with large/huge result cause every thing is loaded into memory.

Answer 3

Building off of Asya's answer: If you wanted a list of just one value in each entry as opposed to a list of objects--using a list comprehension worked for me.

I.e. if each object represents a user and the database stored their email, and you say wanted all the users that were 15 years old

user_emails = [user['email'] for user in db.people.find( {'age' : 15} )]

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