+ this._rollbackBackup = this.root.clone();
+ this._currentTransaction = new Transaction([], metadata);
+ },
+
+ endTransaction: function() {
+ if(!this._currentTransaction) {
+ throw new Error('End of transaction requested, but there is no transaction in progress!');
+ }
+ if(this._currentTransaction.hasTransformations()) {
+ this.undoStack.push(this._currentTransaction);
+ }
+ this._currentTransaction = null;
+ },
+
+ rollbackTransaction: function() {
+ if(!this._currentTransaction) {
+ throw new Error('Transaction rollback requested, but there is no transaction in progress!');
+ }
+ this.replaceRoot(this._rollbackBackup);
+ this._rollbackBackup = null;
+ this._currentTransaction = null;
+ this._transformationLevel = 0;
+ },
+
+ transaction: function(callback, params) {
+ var toret;
+ params = params || {};
+ this.startTransaction(params.metadata);
+ try {
+ toret = callback.call(params.context || this);
+ } catch(e) {
+ if(params.error) {
+ params.error(e);
+ }
+ this.rollbackTransaction();
+ return;
+ }
+ this.endTransaction();
+ if(params.success) {
+ params.success(toret);
+ }
+ return toret;