Both read-only and read-write Transactions can nest to any depth.
The most common examples of transaction nesting occur in the commit phase of the transaction
life-cycle:
trigger commands are executed in nested
read/write transactions and pre- and
post-commit listeners are
called in nested read-only transactions.
Post-commit listeners are called only when a root transaction (on that is not nested in
some other transaction) commits. This is necessary because even after a nested transaction
has committed, its changes can be rolled back if its parent (or some ancestor) rolls back.
Pre-commit listeners are invoked at every level of nesting, because a parent transaction
may assume the data integrity conditions guaranteed by triggers when it resumes following
the commit of a child transaction.
Validation is performed on all changes when a root transaction commits, because it must
include the changes performed by trigger commands in nested transactions. Validation has
the last word in the committing of a transaction.
Inheritance of Transaction Options
The EMF Transaction API defines a number of standard
options
for read/write transactions. Nested transactions inherit these options from their parents.
The standard options cannot be disinherited. For example, if a parent transaction does
not send post-commit notifications, then none of its descendents will, either, even if
they explicitly specify false for that option.
Nested transactions can, however, add options (set them true)
that their parents do not have (or have them set false).
For example, a child transaction can disable notifications. When its parent commits, the
changes that it reports will simply exclude any that occurred during the execution of the
child.
The inheritance of custom options in an
extension of the
transaction API is defined by that extension.
Copyright (c) 2006, 2007 IBM Corporation and others. All Rights Reserved.
