Node MongoDB loop through collection's first record and push it into an array

Question

I am trying to fetch a list of user names by numeric collection names. I have created the query and seems to be working fine but its not pushing into the array so i can return the entire data as response for the api.

router.get('/chat-logs', async (req, res) => {
  const collections = Object.keys(db.db.collections);

  MongoClient.connect(url, { useUnifiedTopology: true }, function(err, dbm) {
    if (err) throw err;
    var dbo = dbm.db('dbname');
    let collections = dbo
      .listCollections()
      .toArray()
      .then(data => {
        let names = [];
        forEach(data, function(e) {
          let { name } = e;
          if (!isNaN(name)) {
            dbo.collection(name).findOne({}, function(err, result) {
              if (err) throw err;
                names[name] = `${result.first_name} ${result.last_name}`;
            });
          }
        });
        console.log(names)
        res.send(names);
      });
  });
});

as you can see I am getting all the collection names because the chat logs are stored with their corresponding ids as a collection, and I am looping through them and fetching their last fields. At the end I am trying to push it inside names[] array so I can collect them all and send the response. The problem is that the array remains empty outside the query scope. I am kind of stuck at this point, I was wondering if there's any much more easier way to get all collections with their last fields as an array, and if not then how can I fix this?

thanks

@CodyＧ looping through the collection names that are numeric — Areg, Jul 13 '20 at 18:09
its there, `collections = dbo.listCollections().toArray().then(data => {` — Areg, Jul 13 '20 at 18:15
Where is `forEach` defined? I see it in the code. It's a function you're calling --- — Cody Ｇ, Jul 13 '20 at 18:17
@CodyＧits javascript built in function https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach — Areg, Jul 13 '20 at 18:17
You're not calling it on an array. you have `let names=[]; forEach(...` — Cody Ｇ, Jul 13 '20 at 18:18
If you want to use the array prototype function I would imagine `data.forEach(function(e){ ... })` or `Array.prototype.forEach.apply/call(data,args)` — Cody Ｇ, Jul 13 '20 at 18:22
k. So you've defined forEach somewhere in your file as some sort of array forEach that takes the array as a first argument and calls the function for each array? — Cody Ｇ, Jul 13 '20 at 18:27
Does this answer your question? [Node JS Promise.all and forEach](https://stackoverflow.com/questions/31413749/node-js-promise-all-and-foreach) — Cody Ｇ, Jul 13 '20 at 18:28

Cody Ｇ · Accepted Answer · 2020-07-14T14:39:51.837

See Node JS Promise.all and forEach

You may be able to do something like this:

router.get('/chat-logs', async (req, res) => {
  const collections = Object.keys(db.db.collections);

  MongoClient.connect(url, { useUnifiedTopology: true }, function(err, dbm) {
    if (err) throw err;
    var dbo = dbm.db('dbname');
    let collections = dbo
      .listCollections()
      .toArray()
      .then(data => {
        let names = [];
        i = 0;
        data.forEach(function(e) {
          let { name } = e;
          if (!isNaN(name)) {
            dbo.collection(name).findOne({}, function(err, result) {
              if (err) throw err;
              names.push(`${result.first_name} ${result.last_name}`);
              i=i+1;
              if(i>(names.length-1)){
                // all callbacks have finished. 
                console.log(names)
                res.send(names);
              }
            });
          }
        });

      });
  });
});

i think there's an error at `names.length` it returns the collection name — Areg, Jul 13 '20 at 18:39

Node MongoDB loop through collection's first record and push it into an array

1 Answers1