Recursive callbacks

Question

Recursive callbacks

Need a little help trying to get this breadcrumb builder working - it's a recursive fetch for parent categories that should return an array of entries. Not quite working and my brain is fried.... currently only returns the last entry.

var walk = function(c, done) {
  var results = [];
  Category.findById(c).exec(function(err, cat) {
    if(cat) {
      results.push({ title: cat.title, id: cat.id});
      if(cat.parent) {
        walk(cat.parent, function(err, res) {
          results = results.concat(res);
        });
      }
      return done(null, results);
    }
    done(results);
  });
};

walk(product.categories[0].id, function(err, results) {
//  if (err) console.log (err);
  console.log(results);
});

javascript
node.js

Answer 1

Unfortunately, recursion and callbacks don't mix all that nicely. You're calling done after retrieving the first category, but you're not waiting for the other calls to walk to complete before calling done. You need to wait for them. I'd do something like this (pseudocode):

fetch this category
    if no subcategories
        call callback with [{ title: ... }] and return
    pending = number of subcategories
    results = [[{ title: ... }]]
    for each subcategory
        recurse
            pending--
            results[index + 1] = subcategory_results
            if none pending
                call callback with the concatenation of the subarrays of results

Answer 2

how about node-fibers? try this.

Good example like this link : mongo-model example

and method synchronize util written coffee-script

Answer 3

Okay got it.... Needed to call done from the inner walk call.

var walk = function(c, done) {
  var results = [];
  Category.findById(c).exec(function(err, cat) {
    if(cat) {
      results.push({ title: cat.title, id: cat.id});
      if(cat.parent) {
        walk(cat.parent, function(err, res) {
          results = results.concat(res);
          done(null, results);
        });
      } else {
         done(null, results);
      }
    } else {
      done('No cat found'); // Error
    }
  });
};