     @static
     @return {String} propName
     ###
+    @_propOfUpdatedAt: undefined
     @getPropOfUpdatedAt: ->
 
         if @_propOfUpdatedAt is undefined

    @static
    @return {Array}
    ###
    @getModelProps: ->

        if not @_modelProps?

        return props


    ###*
    get prop name whose type is CREATED_AT
    notice: only one prop should be enrolled to CREATED_AT
