Persist to DB if the object has changed
Persist to DB if the object has changed

Otherwise, Zun might show an inconsistent state between show
and other operations.

Change-Id: I50f58daef84c68a53aa6912ab4fe57e9a6656da5

kevin-zhaoshuai/zun,kevin-zhaoshuai/zun,kevin-zhaoshuai/zun