callback hell in loop of queries - node.js

Question

i'm trying to get a list of distinct values and count of items. like this:
sheet_kinds: [
"cars" (10 items),
"computers" (23 items),
"utilities" (88 items)
],
so the query to get distinct values is ok. my code:
getValues:function(next){
Sheet.find().distinct('kind', function(err, rs){
for (var i = 0; i < rs.length; i++) {
Sheet.count({kind:rs[i]}, function(err, c){
next(null, rs); <====== THIS IS NOT GOOD
});
};
});
}
I cannot run next() inside a loop, I know. But how can I get a full list of count values and run next() only after all items back?

Answer 1

In this kind of scenario you'd be much better off using async
Install
npm install --save async
Require
var async = require('async');
Use
getValues:function(next){
Sheet.find().distinct('kind', function(err, rs){
async.map(rs, function (item, done) {
Sheet.count({kind:item}, done);
}, next);
});
}
Details
getValues:function(next){
Sheet.find().distinct('kind', function(err, rs){
// async.map is used to map a collection asynchronously
// the cb will be invoked once for each item in rs
async.map(rs, function (item, done) {
// the done callback needs to be invoked exactly once
// in this case, we just pass it to count, since
// the (err, count) result is exactly what we want (getting us the count)
Sheet.count({kind:item}, done);
// next is invoked with the err, if any, and
// the resulting map (an array of counts)
}, next);
});
}
Update
Addresses question in comments
getValues:function(next){
Sheet.find().distinct('kind', function(err, rs){
async.map(rs, function (item, done) {
Sheet.count({kind:item}, function (err, count) {
done(err, {kind:item,count:count});
});
}, next);
});
}