[TYPO3-mvc] Could not get value from SYS_LASTCHANGED

[Dimanche Eat]

Hi all,

I have tried to map my model with table pages, then I want to access a 
few fields to display in my view. Here is my typoscript setup:

config {
	tx_extbase {
		persistence {
			updateReferenceIndex = 1
			classes {
				Tx_XX_Domain_Model_Page {
					mapping {
						tableName = pages
						columns {
							tstamp.mapOnProperty = tstamp
sys_lastchanged.mapOnProperty = sys_lastchanged
						}
					}
				}
			}
		}
	}
}

So, my problem is that I could not get the value from SYS_LASTCHANGED, 
but I can get the value from tstamp.

Is there any special configuration with SYS_LASTCHANGED?

Really appreciate for any input.

Thank you,
Dimanche