The actual saving of an Order object occurs by calling the updateOrder method in the OrderManager. The updateOrder method calls into the PipelineManager to execute the updateOrder pipeline. Each processor in the pipeline saves a different type of commerce object.
For more information about pipelines, the PipelineManager, and the transactional modes and transitions of the processors in the updateOrder pipeline, refer to the updateOrder Pipeline Chain section in the Appendix E: Pipeline Chains.
