MongoDB return True if document exists

python mongodb pymongo tornado-motor
user94628 picture user94628 · Aug 6, 2014 · Viewed 47.5k times · Source

I want to return true if a userID already exists and false otherwise from my collection.I have this function but it always returns True.

def alreadyExists(newID):
    if db.mycollection.find({'UserIDS': { "$in": newID}}):
        return True
    else:
        return False

How could I get this function to only return true if a user id already exists?

Answer

Philipp picture Philipp · Aug 6, 2014

Note: This answer is outdated. More recent versions of MongoDB can use the far more efficient method db.collection.countDocuments. See the answer by Xavier Guihot for a better solution.

find doesn't return a boolean value, it returns a cursor. To check if that cursor contains any documents, use the cursors count-method.

if db.mycollection.find({'UserIDS': { "$in": newID}}).count() > 0.

By the way: is newID an array? When it isn't, you should not use the $in-operator. You can simply do find({'UserIDS': newID})

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