How can I filter an array with the result of the mongoose query?

Question

I would like to filter an array based on a mongoose query. However, I am relatively new to node.js and asynchronous programming. I am aware that Array.prototype.filter is a synchronous function and the mongoose queries are asynchronous.

When searching on this site I came across the following two solutions:

filtering an array with a function that returns a promise - but this looks quite complicated and I don't understand the concept yet.
how to wait for the result of a mongoose query? - at first this solution looks quite understandable, so I gave it a try

here is my example code based on the second approach:

exports.create = function(req, res) {
    async.filter(req.body.data.entries, function(item, callback){
        MyCollection.findOne({'_id': item.id}, function(err, doc) {
            callback(err == null && doc != null);
        });    
    }, 
    function(results){
        req.body.data = results
        // default controller to create a document in Mongo DB
        return controller.create(Model, req, res);
    });
};

However, this does not seem to work. results does not correspond to a filtered list as described in the answer, but corresponds exactly to the result of the Boolean expression of the callback function. I also checked this in the current async documentation to see if anything has changed in the filter function, but didn't see any change.

can you please explain your goal? Do you want to do a mongoose lookup for every element in your array `req.body.data.entries` and these lookups are not dependent on each other. is that right? — Raghav Garg, Sep 13 '18 at 16:20
My intention is to filter out incorrect entries. The data from `req.body.data.entries` is like sensor data that could contain either a sensor entry that may no longer be registered or sensors from another network. So the lookups are not dependent on each other. — nlang, Sep 14 '18 at 14:29

score 1 · Accepted Answer · answered Sep 13 '18 at 17:55

Well, There is another way to do it. Instead of getting rows in async. You can get all the records filtered from database. There is a concept of $in in mongodb. You can use this to retrieve multiple records at a time with specific Ids. In your case, here is the exmaple

exports.create = function(req, res) {
    var ids = []
    req.body.data.entries.forEach(function (item) {
      ids.push(item.id);
    });
    MyCollection.findOne({'_id': {$in: ids}}, function (err, docs) {
      // here you have all your filter data
      var myDocs = docs;

      //Callback from here to return data
    });

  }

Thanks for helping me out. I finally filtered the `req.body.data.entries` with the result from `docs`. — nlang, Sep 14 '18 at 14:56

How can I filter an array with the result of the mongoose query?

1 Answers1