Using Caché Objects - InterSystems Documentation

Object Persistence
Note:
In a multiprocess environment, an application with improper concurrency controls
can use %Save in a way that results in unexpected behavior. For more information,
see the appendix “Object Concurrency Options.”
12.2.1.1 Saving Objects and Transactions
The %Save method automatically saves all the objects in its SaveSet as a single transaction.
If any of these objects fail to save, then the entire transaction is rolled back.
If you wish to save two or more unrelated objects as a single transaction, then you must
enclose the calls to %Save within an explicit transaction: that is, you must start the transaction
using the TSTART command and end it with the TCOMMIT command.
For example:
// start a transaction
TSTART
// save first object
Set sc = obj1.%Save()
// save second object (if first was save)
If ($$$ISOK(sc)) {
Set sc = obj2.%Save()
}
// if both saves are ok, commit the transaction
If ($$$ISOK(sc)) {
TCOMMIT
}
There are two things to note about this example:
1. The %Save method knows if it being called within an enclosing transaction (because
the system variable, $TLEVEL, will be greater than 0).
2. If any of the %Save methods within the transaction fails, the entire transaction is rolled
back (the TROLLBACK command is invoked). This means that an application must test
every call to %Save within a explicit transaction and if one fails, skip calling %Save on
the other objects and skip invoking the final TCOMMIT command.
If you are saving objects from Java, and wish to save multiple objects within the same transaction
(as in the above example) you can use the transactionStart and transactionCommit
methods of the Java Database class.
12.2.1.2 READONLY Objects
It is possible to define persistent objects that can be opened but not saved or deleted. To do
this set the READONLY parameter for the class to 1:
102 Using Caché Objects