MongoDB Result can console.log() but not pushed to array NodeJS

Question

I have a list of users I would like to look up in my MongoDB database and once I look them up, I want to store them in an array so I can do things with the data. I'm using the official mongodb package in NodeJS. Here's the code

var chatsData = []
for (let userID of chatIDs) {
    db.collection('users').find({ '_id': ObjectId(userID) }).toArray((err, result) => {
        if (err) throw err
            chatsData.push(result)
            console.log(result)
        })
    }
}

console.log('vvv Final data in array: vvv')
console.log(chatsData)

When I run the code this, I get this vvv

vvv Final data in array: vvv
[]
[
  {
    _id: 5eae4c90ad1dd6304c69a75a,
    usnm: 'gohjunhao',
    eml: '[email protected]',
    phnm: '00000000',
    pswd: '$2a$10$IUaxiweNrUUwxZP6XEQfFeTTnbta13/kv6DdebwJ0WT/bM.3fc5ay',
    register_date: 2020-05-03T04:46:08.054Z,
    __v: 0
  }
]
[
  {
    _id: 5ead401f8059852114bf9867,
    usnm: 'gfox.2020',
    eml: '[email protected]',
    phnm: '11111111',
    pswd: '$2a$10$UYaEraoI4Kj0dI.nt5Hbr.LgDL1TNtDOsz7tcxETJW7HRtmgWo.UK',
    register_date: 2020-05-02T09:40:47.684Z,
    __v: 0
  }
]

How do I get a proper array of data in my array so it can be used later? Is what I'm doing wrong? Do I need to use a .then() statement or an async await?
Here's the full code

MongoClient.connect(url, { useUnifiedTopology: true }).then(async chooseDB => {
    db = chooseDB.db('nodejs')

    // Get a list of all tables
    db.listCollections().toArray((err, result) => {
        /***** YOU DON'T NEED TO UNDERSTAND THIS PART OF THE CODE ******/
        if (err) throw err
        var chatList = []
        var chatIDs = []
        for (let i = 0; i < result.length; i++) {
            const table = result[i]
            if (table.name.indexOf(data) > 1) {
                // add tables with personal id to chatList
                chatList.push(table.name)
                // add id's of other chats to out table
                chatIDs.push(table.name.replace('dm', '').replace('~', '').replace(data, ''))
            }
        }
        /***** IT'S JUST HOW I GET MY CHAT ID'S *****/

        // Get data on users
        var chatsData = []
        for (let userID of chatIDs) {
            try{
                let temp = await db.collection('users').find({ '_id': toMongoObjectId(userID) }).toArray()
                chatsData.push(temp)
            }
            catch(error) {
                console.log(error)
            }
        }

        console.log('vvv Final data in array: vvv')
        console.log(chatsData)

        toClient.userData = chatsData
        toClient.users = chatList
        socket.emit('res_chatList', toClient)

    })
})

Are you like trying to use the chatsData after this for-loop and it acts like the array is empty? — asosnovsky
– asosnovsky, Commented May 3, 2020 at 5:09
yes. I want the mongo results to be added to chatsData and use it later — zS1L3NT
– zS1L3NT, Commented May 3, 2020 at 5:11

Bhavik Chavda · Accepted Answer · 2020-05-03 06:17:05Z

1

This can be solved using async-await, write async to the function of then block-like,

mongoclient.connect().then( async (cli) => { 
    db = cli.db(dbName);
    ...
})

your logic to fetch data will be

    var chatsData = []
    for (let userID of chatIDs) {
        try{
             let temp = await db.collection('users').find({ '_id': ObjectId(userID) }).toArray();
             chatsData.push(temp);
        }
        catch(error) {
            console.log(error);
        }
   }
   console.log(chatsData);

answered May 3, 2020 at 6:17

Bhavik Chavda

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1 Comment

zS1L3NT Over a year ago

Thank you, back then I didn't understand the concept of async/await

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