Using Q to return secondary query in node with express and mysql - mysql

Question

New to node, As I am cycling through a roster of students, I need to check and see if a teacher has requested them for tutoring.
I realized I can't just do this:
var checkRequest = function(id){
var value = '';
roster.query('SELECT * FROM teacher_request WHERE student_id ='+id, function(err, row){
value = row.length;
}
return value;
}
After a bit of digging around promises looked like a great solution, but if I simply return the deferred.promise from the checkRequest function, all I get is an object that says [deferred promise] which I can't access the actual data from. (Or have not figured out how yet)
If I follow along with their api and use .then (as illustrated in the getRow) function, I am back in the same problem I was in before.
function checkRequest(id) {
console.log(id);
var deferred = Q.defer();
connection.query('SELECT * FROM teacher_request WHERE student_id ='+id, function(err, row){
deferred.resolve(row.length);
});
return deferred.promise;
}
var getRow = function(id){
checkRequest(id).then(function(val) {
console.log(val); // works great
return val; //back to the same problem
});
}
The roster needs to be able to be pulled from an external API which is why I am not bundling the request check with the original roster query.
Thanks in advance

Answer 1

From the stuff you posted, I assume you have not really understood the concept of promises. They allow you to queue up callbacks, that get executed, when the asynchronous operation has finished (by succeeding or failing).
So instead of somehow getting the results back to your synchronous workflow, you should convert that workflow to work asynchronous as well. So a small example for your current problem:
// your students' ids in here
var studentsArray = [ 1, 2, 5, 6, 9 ];
for( var i=0; i<studentsArray.length; i++ ) {
checkRequest( i )
.then( function( data ){
console.log( data.student_id );
// any other code related to a specific student in here
});
}
or another option, if you need all students' data at the same time:
// your students' ids in here
var studentsArray = [ 1, 2, 5, 6, 9 ];
// collect all promises
var reqs = [];
for( var i=0; i<studentsArray.length; i++ ) {
reqs.push( checkRequest( i ) );
}
Q.all( reqs )
.then( function(){
// code in here
// use `arguments` to access data
});