Mongodb没有调用回调

Question

我的nodejs app中有以下代码：

db.open(function(err, db) {
     while (item = stream.read())
     {
        var parsedDate = parseDateFromString(item.title);
        var movieName = parseNameFromString(item.title);
        var channelName = parseChannelFromString(item.title);

        //var doc = { "name": movieName, "channel": channelName, "showed": parsedDate, "showDate": parsedDate.format(), "run_id": new Date().toString()};
        var doc = { "name": movieName, "channel": channelName, "showed": parsedDate, "run_id": new Date().toString()};

        db.collection('programs', function(err, collection) {
           collection.find({'name' : doc.name, "channel" : doc.channel}).count(function(countErr, count) {
             console.log('count!');
              if(count == 0)
                 insertDocument(collection, doc);
              else
                console.log('Found match from db with name ' + matchDoc.name);
            });
         });

      } // End of while
  }); // End of Open

问题就是数！永远不会报道。所以collection.count没有调用它的回调。我检查了collection.find被多次调用。什么可能导致这个问题？