async await is not executing functions sequentially in express nodejs

Question

I want to run 3 database query then render the 3 result objects to view, so I used async await to run queries first but seems its not waiting/working, always sending null objects to view before running queries. Cant find where I went wrong, I am using nodejs 12.16.1, not sure if its es6 supporting issue or sth else.

var express             = require('express');
var router              = express.Router();
var reviewModel         = require.main.require('./models/review-model');
var propertyModel       = require.main.require('./models/property-model');

router.get('/', async function(req, res){
    try{
        req.cookies['username'] == null ? loginCookie = null : loginCookie = req.cookies['username'];
    
        var getPromoteInfo = await propertyModel.getPromoteInfo(function(result){
            if(result!=null) return result;
        });

        var getPromoteReview = await reviewModel.getPromoteReview(function(result2){
            if(result2!=null)  return result2;
        });

        var getLatest3reviews = await reviewModel.getLatest3reviews(function(result3){
            if(result3!=null)  return result3;
        });

        res.render('index', {property:getPromoteInfo, rating:getPromoteReview, testimonials:getLatest3reviews, loginCookie});
    }
    catch(err){console.log(err);}
});

module.exports = router;

Model code:

var db = require('./db');

module.exports = {
    getPromoteInfo: function(callback){
        var sql = "select * from property where promote_status = 1;";
        db.getResult(sql, null, function(result){
            if(result){
                callback(result);
            }else{
                callback(null);
            }
        });
    }
}

Can you show us how e.g. getPromoteInfo is implemented? Apart from that the problem is probably that you're using both await and a callback-function. — eol
– eol, Commented Jun 20, 2020 at 13:55
just updated the question, i was thinking same, might be issue with await+callback — RRR
– RRR, Commented Jun 20, 2020 at 14:03

eol · Accepted Answer · 2020-06-20 14:23:05Z

2

You're using await on a function that does not return a Promise resulting in an undefined value. So in order for async/await to work, you could rewrite getPromoteInfo as follows:

var db = require('./db');

module.exports = {
    getPromoteInfo: function(){
        return new Promise( (resolve, reject) => {
           var sql = "select * from property where promote_status = 1;";
           db.getResult(sql, null, function(result){
              if(result){
                resolve(result);
              }else{
                // you can decide whether to reject or not if no records were found
                reject();
              }
           });
        });
        
    }
}

In your express-handler you can then simply await this function call, without passing a callback:

const getPromoteInfo = await propertyModel.getPromoteInfo();

Note that you can check if your db-client/library supports promises out of the box - then you would not have to wrap your functions manually in a promise.

edited Jun 20, 2020 at 14:23

answered Jun 20, 2020 at 14:10

eol

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1 Comment

RRR Over a year ago

didn't work without promise wrapper, saved my day :)

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