Calling save:
persists changes made to the object graph on the specific context and takes it one level above.
Each context contains its own changeset, and when you call save:
, the changes are either taken one level above (to its parent context), or, if there is no parent context, to the store coordinator to be persisted by the method specified when opening the coordinator (SQLite, XML, binary, etc.).
Changes can be modifications, insertions or deletions.
Before saving, changes to objects are verified and objects are notified about the save process.
After saving, notifications are sent to the system to let know various components (such as fetch results controllers, your code, etc.) that the save operation has taken place.