return variable from a nested callback in node.js

Question

I have the results of my query in result but I can not pass it to browser, it is showing empty. how can I return the result to res.send('result')?

myApp.get('/agg',function(req,res){
MongoClient.connect(url, function(err, db) {
    // Execute aggregate, notice the pipeline is expressed as an Array
    db.collection('projects').aggregate([{$match:{school_state:"DC"}}, {$group:{_id: "$primary_focus_subject",total_amount:{$sum: "$total_donations"}}}],function(err,result){
    console.log(result);

    db.close();
    });
});

res.send(result);

});

mJehanno · Accepted Answer · 2017-04-29 16:31:42Z

1

You have 2 solutions :

put res.send(result); where you have console.log(result)

having a promise wrapping your MongoClient.connect like this :

let promise = new Promise((resolve,reject)=>{
  MongoClient.connect(url,function(err,db){
    db.collection('projects').aggregate([{$match:{school_state:"DC"}}, {$group:{_id: "$primary_focus_subject",total_amount:{$sum: "$total_donations"}}}],function(err,result){
      if(err) reject(err)
      resolve(result);
    });
  });    
})

answered Apr 29, 2017 at 16:31

mJehanno

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