code: function(aDimensionName) {
  			if (!aDimensionName) {
  				return;
  			}
  
  			this._oSelectedPropertyNames = null; // reset previously compiled list of selected properties
  
  			for (var i = -1, sDimName; (sDimName = aDimensionName[++i]) !== undefined;) {
  				if (!this._oQueryResult.findDimensionByName(sDimName)) {
  					throw sDimName + " is not a valid dimension name"; // TODO
  				}
  				this._oAggregationLevel[sDimName] = {
  					key : true,
  					text : false,
  					attributes : null
  				};
  			}
  		}
docs: Add one or more dimensions to the aggregation level
  
  @param aDimensionName
  Array of dimension names to be added to the already defined
  aggregation level.
  
  @public
  @function
  @name sap.ui.model.analytics.odata4analytics.QueryResultRequest#addToAggregationLevel