return value from a function with asynchronous commands

Question

I'm writing a NodeJS v0.10 application with MariaSQL.

i want to create a function that returns the id of a row, and if the row doesn't exist, to create it and then return the id.

this is what I have so far:

TuxDb.prototype.createIfNEDrinkCompany = function(drinkCompany) {
 this.client.query("insert into drink_company(drink_company_name) values(:drink_company) on duplicate key update drink_company_id=drink_company_id",
    {'drink_company' : drinkCompany})
    .on('result',function(res) {
    res.on('end',function(info){
        if (info.insertId > 0) {
                return info.insertId;
        } else {
            this.client.query("select drink_company_id from drink_company where drink_company_name = :drink_company",{'drink_company' : drinkCompany})
                .on('result',function(res){
                    res.on('row',function(row){
                        return row.drink_company_id;
                    });
                });
        }
    });
    });

}

now the problem is that since it's asynchronous, the function ends before the value is returned.

how can I resolve this issue ?

you've added a new tag called mariasql would you mind telling me what it is? googling didn't turn up much. — gideon
– gideon, Commented Jan 9, 2015 at 6:24

Community · Accepted Answer · 2017-05-23 11:57:54Z

1

The standard way in nodejs of dealing with async code is to provide a callback function as a last argument to your method and call it whenever your asynchronous finishes. The callback function standard signature is (err, data) - you can read more about here: Understanding callbacks in Javascript and node.js

Rewriting your code:

TuxDb.prototype.createIfNEDrinkCompany = function(drinkCompany, callback) { 
 this.client.query("insert into drink_company(drink_company_name) values(:drink_company) on duplicate key update drink_company_id=drink_company_id",
    {'drink_company' : drinkCompany})
    .on('result',function(res) {
    res.on('end',function(info){
        if (info.insertId > 0) {
                callback(null, row.drink_company_id);
        } else {
            this.client.query("select drink_company_id from drink_company where drink_company_name = :drink_company",{'drink_company' : drinkCompany})
                .on('result',function(res){
                    res.on('row',function(row){
                        callback(null, row.drink_company_id);
                    });
                });
        }
    });
    });

}

and then in the code calling your method

db.createIfNEDrinkCompany(drinkCompany, function(err, id){
    // do something with id here
})

edited May 23, 2017 at 11:57

CommunityBot

11 silver badge

answered Jan 8, 2015 at 15:15

lukaszfiszer

2,6511 gold badge21 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Robert Levy Over a year ago

promises are an alternative pattern

Collectives™ on Stack Overflow

return value from a function with asynchronous commands

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related