Mysql-nodejs nested queries

Question

It says that cannot read property authorid undefined in socket.broadcast line.

setInterval(function(){
    db.query("select * from `notifications`", function(err, rows){
        if (rows.length>temp){

            for (var i=temp; i<rows.length; i++){
                console.log('sending room post', rows[i].authorid);
                db.query("select `name` from `users` where `id`=?", [rows[i].authorid ], function(err, name){
                    name=name[0].name;
                    socket.broadcast.to(rows[i].authorid).emit('new notification', {
                        authorname:name,
                        dpid:rows[i].followid,
                        read:rows[i].read,
                        type:rows[i].type,
                        followstatus:1
                    }); 
                });


            }
            temp=rows.length;
        }
    })
}, 3000);

Answer 1

The problem is that the value of i is rows.length when using the socket.

You can fix this by creating a function to which you send the current row or send the index and use rows[index]:

setInterval(function() {
    db.query("select * from `notifications`", function(err, rows) {

        // You access the values of the current row
        // row.authorid
        // ...
        var broadcast = function(row) {
            console.log('sending room post', row.authorid);
            db.query("select `name` from `users` where `id`=?", [row.authorid], function(err, name) {
                name=name[0].name;
                socket.broadcast.to(row.authorid).emit('new notification', {
                    authorname:   name,
                    dpid:         row.followid,
                    read:         row.read,
                    type:         row.type,
                    followstatus: 1
                }); 
            });
        };

        if (rows.length>temp) {
            for (var i=temp; i<rows.length; i++) {
                broadcast(rows[i]);
            }
            temp=rows.length;
        }
    })
}, 3000);