code: function initialize(config, callback, config_helper) {
    config_helper = config_helper || require('../config/index');
  
    if(!checkConfSanity(config)) {
      callback(new Error('conf.dbopt is not sane, can\'t initialize composite adapter'));
      return;
    }
  
    populateDatabasesArray(config, config_helper, function(err, databases) {
      if(err)
        return callback(err);
      var adapter = new Compositeadapter(config, databases);
      callback(null, adapter);
    });
  }
docs: A composite adapter that consists of multiple adapters.
  The adapters may be of a different type.
  
  `config.dbopt` should be an array containing JSON-objects
  that will be used to initialize the individual adapters. This function
  uses config/index.js's initializeDb-function to initialize the adapters.
  
  @param {Object} config - Configuration object as passed from config.js
  @param {Function} callback
  @param {Object} config_helper - A helper to use for initializing adapters (for testing)