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I'm trying to fetch large data from mongodb

There is my code

    let cont = 0
    const stream = await dataModel.find({}).lean().cursor(); // it will return around 2.000 elements
    console.log("Checkpoint one")

    await stream.on('data', async (res) => {
       try {

         cont += 1


       } catch (e) {
         console.log(e)
       }
    });

    await stream.on('close', () => {
      console.log(`Execution ended. Number of elements: ${cont}.`);
    });

    console.log("Checkpoint two")

Output: 

Checkpoint one
Checkpoint two
Execution ended. Number of elements: 2194.

Expected output:

Checkpoint one
Execution ended. Number of elements: 2194.
Checkpoint two

When I'm trying to console log each res inside "on data" function, its also console logging after "Checkpoint two",

KrystianK
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  • This will help you https://stackoverflow.com/questions/52534679/why-even-after-using-async-await-for-multiple-calls-still-got-empty-response – Ashh Oct 02 '18 at 06:09

1 Answers1

1

javascript stream.on('close', () => { console.log(`Execution ended. Number of elements: ${cont}.`); }); This DEFINES (not "executes") a function (that is called each time a stream is closed) and then directly moves on with code-execution. You cannot await this, you also cannot await the stream.on('data') because that's the same issue. If you want your parent function to wait to a point where the stream has finished reading, you could create a new Promise which is fullfilled by your stream.on('close') function. You can then await that promise just before your console.log("Checkpoint two"). This should work, you maybe wanna give it a try.

mhombach
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