Amazing example of async waterfall and map for cheating in nested result queries

gistfile1.txt

// Use waterfall so that you can easily disconnect at the end of your code.
// It also makes node.js callbacks less confusing.
async.waterfall([
  function (wCb) {
    connection.connect();
    // wCB is a callback function. Call it when you want to move to the
    // next function in the waterfall
    wCb();
  },
  function (wCB) {
    connection.query('SELECT id, name FROM pages', function(err, pages, fields) {
      if (err) {
        // If you pass a first parameter in wCB, it will move to the
        // last function of the waterfall and treat that as an error.
        return wCB(err);
      } else {
        // Optionally, you can pass a second, third, etc. parameter
        // which is carried over to the next waterfall function.
        wCB(null, pages);
      }
    });
  },
  function (pages, wCB) { // Notice that the first parameter is not wCB!
    // async.map lets us apply a function to a collection.
    async.map(pages, function (page, mCB) {
      // We can query to simulate a "join" and add it as a property of our object.
      // Since the object is referenced, anything that we write on the object
      // will be reflected outside the async.map.
      connection.query(
        'SELECT id, name FROM sections WHERE page_id = ?',
        page.id,
        function(err, sections, fields) {
          if (err) return mCB(err);

          page.sections = sections;
          mCB();
        }
      );
    }, function (err) {
      // Finally, we invoke our callback function to move to the
      // next waterfall function. Since there's none, it will go
      // to the "ending" function.
      if (err) {
        wCB(err);
      } else {
        // We can still pass a parameter as usual.
        wCB(null, pages);
      }
    });
  }
], function (err, pages) {
  // Unlike the normal waterfall functions, this has a different signature with "err" always first

  if (err) throw err;

  // We can now close our mysql connection
  connection.end();


  console.log(pages);
});

From: http://www.reddit.com/r/node/comments/26cr5v/how_to_get_a_nested_json_like_this_with_nodejs/