How to correctly use async/await using JS/node

Question

I am trying to create a script that will populate my Mongo database using data returned from a few API calls. Ideally, this would be run manually every once in a while or on a scheduler to update the database with fresh data, so I am trying to do everything inside of the 'MongoClient.conncect' function. I would like to import this data one API call at a time and am trying to avoid the ugliness of chained promises and .then's. I have done some research on using async/await and it seems to me that using the 'await' keyword is effectively unwrapping the returned promise. If that is the case, I can't quite figure out why it is not waiting properly. Here is what I have so far:

const MongoClient = require('mongodb').MongoClient;
const fs = require('fs');
const assert = require('assert');
const ProPublicaAPI = require('./ProPublicaAPI');
var constants = require('../common/constants');
var https = require('https');

const url = 'mongodb://localhost:27017';


dbName = 'government';

MongoClient.connect(url, function(err, client) {
  assert.equal(null, err);
  console.log('successfully connected to mongoDB server: ' + url);

  const db = client.db(dbName);
  try{
    var senateInsert = waitInsert(db, 'senate');
  }
  catch(err) {
    console.log(err);
  }
  console.log('closing database connection');
  client.close();
})

async function waitInsert(db, collection) {
  //I made this function just to call inside the MongoClient.connect() above
  return await insertSenateDocuments(db, collection);
}

function insertSenateDocuments(db, chamber) {
  return new Promise(function(resolve) {
    var collection = db.collection(chamber);
    //method that calls API, to be converted into async/await later
    senateMembers = ProPublicaAPI.getAllMembersByChamber(chamber);
    senateMembers.then(function(promisedMembers) {
      console.log("Recieved data from api");
      collection.insertMany(promisedMembers, function(err, result) {
        if(err) return console.log(err);
        console.log(`Imported ${chamber} data`);
        resolve(result);
      });
    })
  })
}

And here is the stack trace:

successfully connected to mongoDB server: mongodb://localhost:27017
about to close
Recieved collection Data
{ MongoError: server instance pool was destroyed
    at basicWriteValidations (D:\Dev\node\node_modules\mongodb-core\lib\topologies\server.js:636:41)
    at Server.insert (D:\Dev\node\node_modules\mongodb-core\lib\topologies\server.js:737:16)
    at Server.insert (D:\Dev\node\node_modules\mongodb\lib\topologies\topology_base.js:315:25)
    at executeCommands (D:\Dev\node\node_modules\mongodb\lib\bulk\ordered.js:525:23)
    at executeOperation (D:\Dev\node\node_modules\mongodb\lib\utils.js:408:22)
    at OrderedBulkOperation.execute (D:\Dev\node\node_modules\mongodb\lib\bulk\ordered.js:602:10)

    at bulkWrite (D:\Dev\node\node_modules\mongodb\lib\collection.js:627:8)
    at executeOperation (D:\Dev\node\node_modules\mongodb\lib\utils.js:408:22)
    at Collection.insertMany (D:\Dev\node\node_modules\mongodb\lib\collection.js:512:10)
    at D:\Dev\node\dataimporter\mongo.js:39:18
  name: 'MongoError',
  message: 'server instance pool was destroyed' }
PS D:\Dev\node\dataimporter> node mongo
successfully connected to mongoDB server: mongodb://localhost:27017
closing database connection
Recieved data from api
{ MongoError: server instance pool was destroyed
    at basicWriteValidations (D:\Dev\node\node_modules\mongodb-core\lib\topologies\server.js:636:41)
    at Server.insert (D:\Dev\node\node_modules\mongodb-core\lib\topologies\server.js:737:16)
    at Server.insert (D:\Dev\node\node_modules\mongodb\lib\topologies\topology_base.js:315:25)
    at executeCommands (D:\Dev\node\node_modules\mongodb\lib\bulk\ordered.js:525:23)
    at executeOperation (D:\Dev\node\node_modules\mongodb\lib\utils.js:408:22)
    at OrderedBulkOperation.execute (D:\Dev\node\node_modules\mongodb\lib\bulk\ordered.js:602:10)
    at bulkWrite (D:\Dev\node\node_modules\mongodb\lib\collection.js:627:8)
    at executeOperation (D:\Dev\node\node_modules\mongodb\lib\utils.js:408:22)
    at Collection.insertMany (D:\Dev\node\node_modules\mongodb\lib\collection.js:512:10)
    at D:\Dev\node\dataimporter\mongo.js:39:18
  name: 'MongoError',
  message: 'server instance pool was destroyed' }

As you can see, the client.close() is being called before the inserting of the documents is taking place.

var senateInsert = waitInsert(db, 'senate'); this line does not wait for your async calls. you have to declare it. you may consider doing connect in a function too — scetiner
– scetiner, Commented Feb 7, 2018 at 8:31
could you please try var senateInsert = await waitInsert(db, 'senate'); instead var senateInsert = waitInsert(db, 'senate'); and let me know the result — kirecligol
– kirecligol, Commented Feb 7, 2018 at 8:31
Thank you, I will try this. However, I am curious, if await is 'unwrapping' the Promise and I am returning it in waitInsert, why then do I have to call await again when I call waitInsert? Is there a way to do this without having to use waitInsert at all and just directly call insertSenateDocuments? — Ben
– Ben, Commented Feb 7, 2018 at 17:19

Quentin · Accepted Answer · 2019-12-13 11:40:20Z

3

You have to await for waitInsert

MongoClient.connect(url, async function(err, client) {
  assert.equal(null, err);
  console.log('successfully connected to mongoDB server: ' + url);

  const db = client.db(dbName);
  try{
    var senateInsert = await waitInsert(db, 'senate');
  }
  catch(err) {
    console.log(err);
  }
  console.log('closing database connection');
  client.close();
})

edited Dec 13, 2019 at 11:40

Quentin

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answered Feb 7, 2018 at 8:32

Dathan

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Comments

Albert Safiullin · Accepted Answer · 2019-12-13 11:38:35Z

0

Easier:

bulkWriteItems(array, collection) {
    return collection.bulkWrite(array, {ordered: true, w: 1})
}

Call:

async saveData() {
    let bulk = [];
    for (let i = 0; i < 100; i++) {
        let name = `item${i}`
        bulk.push({insertOne: {name}});
    }
    return db.collection(COLLECTION_OBJECTS).then(collection => this.bulkWriteItems(bulk, collection))
}

edited Dec 13, 2019 at 11:38

answered Aug 29, 2018 at 18:43

Albert Safiullin

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