CODEWITHSUNDEEP
javascriptnode.jsmongodbmongoosesynchronous
jjwon
jjwon

Reputation: 204

Grabbing and sending elements from MongoDB in Node.js server response

In my Express route, I am trying to return a list of elements that I am grabbing from MongoDB using Mongoose. I'm basically iterating through an array of items, and making MongoDB calls to get the parameter objects that each item has. However, I'm having trouble making sure that I get all the parameters before I send the response. I've tried using promises, other async library functions, etc, but none of them have seemed to work.

The current iteration of the code looks like this (I have tried a lot of different things):

exports.findAll = function(req, res){
  Flow.find({}, function(err, items) {
    console.log(items);
    var payload = {}
    var params = [];

    for (var i=0; i < items.length; i++) {
      var count2 = 0;
      async.whilst(
        function() {
          return ((items[i]) && (count2 < items[i].params.length));
        },
        function(callback) {
          Parameter.findById(items[i].params[count2], function(err, out) {
            params.push(out);
            count2++;
            callback();
          });
        },
        function(err) {
          console.log(params);
          var payload = {
            "flows": items,
            "params": params
          };

          res.send(payload);
          console.log('success: flows found');
        }
      );
    }

This code sends a payload with params not being completely full.

What would be a good way to deal with this? Honestly I just want these database calls to be synchronous, but I just can't figure out how to make this work.

Upvotes: 0

Views: 506

Answers (1)

Neil Lunn
Neil Lunn

Reputation: 151072

This doesn't really seem necessary as you can actually use the $in operator with all the results from your first query:

Flow.find({},function(err,items) {

    var ids = [];

    // blocking? yes, but should be minor - do better if there are problems
    for ( var i=0; i < items.length; i++ ) {
       for ( var n=0; n < items[i].params.length; n++ ) {
           ids.push( items[i].params[n] );
       }
    }

    Parameter.find({ "_id": { "$in": ids } },function(err,params) {
        res.send({ "flows": items, "params": params });
    });

});

So there should be no reason to execute multiple queries inside an async loop, or loops as your code seems to be missing as the direct cause of the problem there.

Upvotes: 1

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