Question

It should be very awesome to use non-blocking code but I’m running out of ideas how to acomplish this task. I have to validate a value by making few db queries like so:

validate = function() {
  var valid = true;
  db.collection('posts').findOne({date: ....}, function(err, post){ 
    if (..) valid = false
  }
  db.collection('posts').findOne({author: .....}, function(err, post){
    if (..) valid = false
  }
  return valid;
}

It is very good that validations can run in concurent manner, but the problem is how to return the final state. Obviously my example will not work. The function will return before db queries execution.

Answer 1

Welcome to the async world.

You should use something like async or fnqueue for your control flow,
then you can setup a chain of validations.

function isValid (mainCallback) {
  new FnQueue({
    date: function (callback) {
      if (...) {
        callback();
      } else {
        callback(new Error('what\'s happened here');
      }
    },
    author: function (callback) {
      db.collection('posts').findOne({ author: ..... }, callback);
    }
  },
  function (err, data) {
    mainCallback(Boolean(err)); //you should more than this :)
  },
  1 // concurrency level for serial execution
);