Extract sub object in array of a document with pymongo

Question

I have multiple documents and each document has a set of tweets. I can find the document by name as follows:

client = MongoClient('localhost', 27017)
db = client['sample_app']
s = db['s']
s.find(
            {
                "name": "temp16"
            }
        )

When I run the above query I get the following data:

{"_id": {"$oid": "5e57db66c6bb04eb902589a2"}, "name": "temp16", "tweets": [{"tweet_id": "1234762637361086465", "tweet_text": "Had an extensive review regarding preparedness on the COVID-19 Novel Coronavirus. Different ministries & states are working together, from screening people arriving in India to providing prompt medical attention.", "tweet_handle": "@narendramodi", "labels": ["A", "B", "C", "D", "E"]}, {"tweet_text": "There is no need to panic. We need to work together, take small yet important measures to ensure self-protection.", "tweet_id": "1234762662413660165", "tweet_handle": "@narendramodi", "labels": ["A", "B", "C", "D", "E", "F"]}]}

My intention is to get the tweet with id "1234762662413660165" in this document alone. So I try the following:

s.find(
            {
                "name": "temp16",
                'tweets': {"tweet_id": "1234762662413660165"}
            },
        )

However I get None

What am I doing wrong?

Belly Buster · Accepted Answer · 2020-03-04 10:14:33Z

1

You need to use $elemMatch

import pymongo
db = pymongo.MongoClient()['mydatabase']
db.mycollection.insert_one({"name": "temp16", "tweets": [{"tweet_id": "1234762637361086465", "tweet_text": "Had an ...", "tweet_handle": "@narendramodi", "labels": ["A", "B", "C", "D", "E"]}, {"tweet_text": "There is ...", "tweet_id": "1234762662413660165", "tweet_handle": "@narendramodi", "labels": ["A", "B", "C", "D", "E", "F"]}]})

tweets = db.mycollection.find({"name": "temp16", 'tweets': {'$elemMatch': {"tweet_id": "1234762662413660165"}}})

for tweet in tweets:
    print(tweet)

answered Mar 4, 2020 at 10:14

Belly Buster

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4 Comments

virupaksha Over a year ago

Hi, thank you for the answer, but I am getting the whole document

virupaksha Over a year ago

I only want the tweet

virupaksha Over a year ago

db.mycollection.find({"name":"temp16"}, {"tweets":{"$elemMatch": {"tweet_id": "1234762662413660165"}}}) worked for me

Belly Buster Over a year ago

If you just want the tweet text you can change the last line to print(tweet.get('tweets')[0].get('tweet_text'))

Dĵ ΝιΓΞΗΛψΚ · Accepted Answer · 2020-03-04 10:32:06Z

0

here's two ways of doing it using aggregation pipelines:

db.collection.aggregate(
    { $match: { name: 'temp16' } },
    { $unwind: '$tweets' },
    { $match: { 'tweets.tweet_id': '1234762662413660165' } },
    { $replaceWith: '$tweets' }
)

db.collection.aggregate(
    { $match: { name: 'temp16' } },
    {
        $replaceWith: {
            $arrayElemAt: [
                {
                    $filter: {
                        input: "$tweets",
                        as: "tweet",
                        cond: { $eq: ["$$tweet.tweet_id", '1234762662413660165'] }
                    }
                }, 0]
        }
    }
)

first one is short and sweet but it has the added overhead of unwinding and creating documents in memory.

edited Mar 4, 2020 at 10:32

answered Mar 4, 2020 at 10:24

Dĵ ΝιΓΞΗΛψΚ

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2 Comments

virupaksha Over a year ago

Thank you for the answer, I can do it in mongo shell but unable to replicate in pymongo

Dĵ ΝιΓΞΗΛψΚ Over a year ago

i'm not familiar with pymongo, but this seems to be how you run aggregation pipelines with it. basically just supply each stage as an array item.

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