> s Obj=##class(User).%OpenId( 1 )
> s Obj.SomeProperty = "New Value" //старое значение - Old Value
>&SQL(SELECT SomeProperty INTO : Obj2("SomeProperty") FROM User WHERE %ID= 1 )
>set:SQLCODE'= 0  Obj2("SomeProperty")=""
> w Obj2("SomeProperty")
Old Value

Class User {
...
Property Shadow As User [ Transient ];
Property ShadowIsLoad As %Boolean [ InitialExpression =  0 ,Transient ];
..
}

Method %OnOpen() As %Library.Status 
{
 set:i%ShadowIsLoad= 0  i%Shadow=..%ConstructClone(),i%ShadowIsLoad= 1 
}

> s Obj=##class(User).%OpenId( 1 )
> s Obj.SomeProperty = "New Value" //старое значение - Old Value
> w Obj.Shadow.SomeProperty," -> ",Obj.SomeProperty,!
Old Value -> New Value

Method %OnAddToSaveSet(depth As %Integer =  3 , insert As %Integer =  0 , callcount As %Integer =  0 ) As %Status [ Private ]
{
 .....
 set i%Shadow="",i%ShadowIsLoad= 0 
 quit $$$OK
}

Method %OnBeforeSave(ins As %Library.Boolean =  0 ) As %Library.Status
{
 .....
 set i%Shadow="",i%ShadowIsLoad= 0 
 quit $$$OK
}

Method %OnAfterSave(ins As %Library.Boolean =  0 ) As %Library.Status
{
 .....
  set:i%ShadowIsLoad= 0  i%Shadow=..%ConstructClone(),i%ShadowIsLoad= 1 
}

Property Shadow As %String [ Transient ];
или
Property Shadow As %CacheString [ Transient ];