When to close MongoDB database connection in Nodejs

Question

Working with Nodejs and MongoDB through Node MongoDB native driver. Need to retrieve some documents, and make modification, then save them right back. This is an example:

Answer 1

Here's a potential solution based on the counting approach (I haven't tested it and there's no error trapping, but it should convey the idea).

The basic strategy is: Acquire the count of how many records need to be updated, save each record asynchronously and a callback on success, which will decrement the count and close the DB if the count reaches 0 (when the last update finishes). By using {safe:true} we can ensure that each update is successful.

The mongo server will use one thread per connection, so it's good to either a) close unused connections, or b) pool/reuse them.

db.open(function (err, db) {
  db.collection('foo', function (err, collection) {
    var cursor = collection.find({});
    cursor.count(function(err,count)){
      var savesPending = count;

      if(count == 0){
        db.close();
        return;
      }

      var saveFinished = function(){
        savesPending--;
        if(savesPending == 0){
          db.close();
        }
      }

      cursor.each(function (err, doc) {
        if (doc != null) {
          doc.newkey = 'foo'; // Make some changes
          db.save(doc, {safe:true}, saveFinished);
        }
      });
    })
  });
});