Question 117448 in Mongodb Question posted in
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How to find_one in mongodb if the key is not always present?

I have a following mongodb:

some records looks like {'_id': ObjectId('62790ce20375a639af1d8676'), 'visit_id': 594817704, 'transaction' : 10}

some has only this form: {'_id': ObjectId('62790ce20375a639af1d8679'), 'visit_id': 594817704}

Using this code I can search for all collections that consists of transaction_id:

collection.find({'transaction_id': { "$exists":True }

But if I would like to get a record with specific transaction_id, this code does not work (it tooks infinite time to search):

collection.find({'transaction_id': 10})

I tried to combine both approaches, that is to firstly ask if transaction_id exists and then search for transaction_id = 10, but it did not work:

collection.find({'transaction_id': { "$exists":True }, 'transaction_id': 10})

How can I fix it, please?

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2

Answers


  1. 0 
    collection.findOne({transaction_id: 10})

    should work.

    No need for $exists if you want a specific value.

    See how it works on the playground example

    How big is your data set? do you have an index on transaction_id?

    If your query is slow, consider add an hashed index on transaction_id.
    Without the index, the DB should check all documents to see if any of them has transaction_id: 1000. This is O(n) operations where n is the number of your documents. The index stores this information, so it will be one check only O(1).

    In order to create the index use the UI or, using the shell:

    db.getCollection(<collectionName>).createIndex( {transaction_id: "hashed" })

    Where you replace <collectionName> with your collection name.

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  2. 0

    Please refer my code.

    from pymongo import MongoClient

client = MongoClient('localhost', 27017);

#connect to the DB named testdb
mydatabase = client.testdb

#pickup collection named transactions 
collection = mydatabase.transactions

#find one by transaction_id
res = collection.find_one({transaction_id:10})

#display data
print(res)

    To create index

    collection.create_index("transaction_id");
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