anchor.diff:  import 'package:mongo_dart/mongo_dart.dart' as mongo_connector;
   
   import 'package:logging/logging.dart';
  -
   
   class MongoDBAdapter extends DBAdapter {
     final Logger log = new Logger('MongoDBAdapter');
  
positive.code:   Future<int> getNextSequence(Table table, Field field) {
      Completer completer = new Completer();
  
      log.finest('Get next sequence:' + table.toString() + ' ' +
      field.toString());
  
      String seqName = "${table.tableName}_${field.fieldName}_seq";
  
      Map command = {
          'findAndModify': 'counters',
          'query': {
              '_id': seqName
          },
          'update': {
              r'$inc': {
                  'seq': 1
              }
          },
          'new': true
      };
  
      _connection.executeDbCommand(
          mongo_connector.DbCommand.createQueryDbCommand(_connection, command))
      .then((Map result) {
        log.finest('Get next sequence result:');
        log.finest(result);
  
  
negative.code:     log.finest('Create sequence:' + table.toString() + ' ' + field.toString());
      var countersCollection = await _connection.collection('counters');
  
      var existingCounter = await countersCollection.findOne(mongo_connector.where
          .eq('_id', "${table.tableName}_${field.fieldName}_seq"));
      if (existingCounter == null) {
        var insertResult = await countersCollection.insert(
            {'_id': "${table.tableName}_${field.fieldName}_seq", 'seq': 0});
  
        log.finest('Create sequence insert result:', insertResult);
      }
  