Savepoints allow for fine grained control over the transactional behavior of your application. Kodo's savepoint API allow you to set intermediate rollback points in your transaction. You can then choose to rollback changes made only after a specific savepoint, then commit or continue making new changes in the transaction. This feature is useful for multi-stage transactions, such as editing a set of objects over several web pages or user screens. Savepoints also provide more flexibilty to conditional transaction behavior, such as choosing to commit or rollback a portion of the transaction based on the results of the changes. This chapter describes how to use and configure Kodo savepoints.
have the following methods to control savepoint behavior.
Note that the savepoints work in tandem with the current
transaction. This means that savepoints require an open transaction,
and that a rollback of the transaction will rollback all of
the changes in the transaction regardless of any savepoints set.
void setSavepoint (String name); void releaseSavepoint (String name); void rollbackToSavepoint (String name);
To set a savepoint, simply call
passing in a symbolic savepoint name.
This savepoint will define a point at which you can preserve
the state of transactional objects for the duration of the current
Having set a named savepoint, you can rollback changes made after that
point by calling
method will keep the current transaction active,
while restoring all transactional instances back to their saved state.
Instances that were deleted after the save point will no longer
be marked for deletion. Similarly, transient instances that were
made persistent after the savepoint will become transient again.
Savepoints made after this savepoint will be released and no longer
valid, although you can still set new savepoints. Savepoints will also
be cleared after the current transaction is committed or rolled back.
If a savepoint is no longer needed, you can release any resources
such as in memory state and datastore resources by calling
This method should not be called for savepoints that have been
released automatically through other means, such as commit of a
transaction or rollback to a prior savepoint. While savepoints
made after this savepoint will also be released, there are no other
effects on the current transaction.
The following simple example illustrates setting, releasing, and rolling back to a savepoint.
Example 9.8. Using Savepoints
import org.apache.openjpa.persistence.*; ... OpenJPAEntityManager oem = OpenJPAPersistence.cast (em); oem.getTransaction ().begin (); Magazine mag = oem.find (Magazine.class, id); mag.setPageCount (300); oem.setSavepoint ("pages"); mag.setPrice (mag.getPageCount () * pricePerPage); // we decide to release pages since price depends on pages. oem.releaseSavepoint ("pages"); oem.setSavepoint ("price"); mag.setPrice (testPrice); ... // we determine the test price is not good oem.rollbackToSavepoint ("price"); // the price is now restored to mag.getPageCount () * pricePerPage oem.getTransaction ().commit ();
import kodo.jdo.*; ... KodoPersistenceManager kpm = KodoJDOHelper.cast (pm); kpm.currentTransaction ().begin (); Magazine mag = (Magazine) kpm.getObjectById (id, true); mag.setPageCount (300); kpm.setSavepoint ("pages"); mag.setPrice (mag.getPageCount () * pricePerPage); // we decide to release pages since price depends on pages. kpm.releaseSavepoint ("pages"); kpm.setSavepoint ("price"); mag.setPrice (testPrice); ... // we determine the test price is not good kpm.rollbackToSavepoint ("price"); // the price is now restored to mag.getPageCount () * pricePerPage kpm.currentTransaction ().commit ();
Kodo uses the
plugin to handle
perserving the savepoint state. Kodo includes the following
in-mem: The default. This is an alias
kodo.kernel.InMemorySavepointManager. This plugin stores all state, including field
values, in memory. Due to this behavior, each set savepoint
is designed for small to medium transactional object counts.
jdbc: This is an alias for the
This plugin requires
JDBC 3 and
java.sql.Savepoint support to operate. Note that
this plugin implements savepoints by issuing a flush to the
oracle: This is an alias for the
This plugin operates similarly to the
plugin; however, it uses Oracle-specific calls.
This plugin requires using the Oracle JDBC driver and database,
9.2 or higher. Note that this
plugin implements savepoints by issuing a flush to the database.