code: function(key, done) {
        if(!this._key) {
          done('no key found for metadata');
          return;
        }
        var ret = null; // if not found return null
        for(var i = 0; i < this._data.length; i++) {
          if(this._data[i][this._key.getName()] === key) {
            ret = this._clone(this._data[i]);
            break;
          }
        }
        done(null, ret);
      }
docs: return an item by id
  @param  {String}   key  The key value
  @param  {Function} done The callback when done