org.odmg
Interface Transaction

All Known Subinterfaces:

TransactionExt

All Known Implementing Classes:

J2EETransactionImpl, NarrowTransaction, TransactionImpl

public interface Transaction

This interfaces provides the operations necessary to perform database transactions. All access, creation, and modification of persistent objects and their fields must be done within a transaction. Before performing any database operations, a thread must explicitly create a transaction object or associate itself with an existing transaction object (by calling join), and that transaction must be open (through a call to begin). All subsequent operations by the thread, including reads, writes, and lock acquisitions, are done under the thread’s current transaction.

A thread may only operate on its current transaction. For example, a TransactionNotInProgressException is thrown if a thread attempts to begin, commit, checkpoint, or abort a transaction prior to joining itself to that transaction.

A transaction is either open or closed. A transaction is open if a call has been made to begin, but no call has been made to commit or abort. Once commit or abort is called, the transaction is closed. The method isOpen can be called to determine the state of the transaction.

Read locks are implicitly obtained on objects as they are accessed. Write locks are implicitly obtained as objects are modified. Transaction objects are transient, they cannot be stored in the database.

Version:

ODMG 3.0

Author:

David Jordan (as Java Editor of the Object Data Management Group)

See Also:

TransactionNotInProgressException

Field Summary

static int	READ Read lock mode.
static int	UPGRADE Upgrade lock mode.
static int	WRITE Write lock mode.

Method Summary

void	abort() Abort and close the transaction.
void	begin() Start a transaction.
void	checkpoint() Commit the transaction, but reopen the transaction, retaining all locks.
void	commit() Commit and close the transaction.
boolean	isOpen() Determine whether the transaction is open or not.
void	join() Attach the caller's thread to this Transaction and detach the thread from any former Transaction the thread may have been associated with.
void	leave() Detach the caller's thread from this Transaction, but do not attach the thread to another Transaction.
void	lock(java.lang.Object obj, int lockMode) Upgrade the lock on the given object to the given lock mode.
boolean	tryLock(java.lang.Object obj, int lockMode) Upgrade the lock on the given object to the given lock mode.

Field Detail

READ

static final int READ

Read lock mode.

See Also:

Constant Field Values

UPGRADE

static final int UPGRADE

Upgrade lock mode.

See Also:

Constant Field Values

WRITE

static final int WRITE

Write lock mode.

See Also:

Constant Field Values

Method Detail

join

void join()

Attach the caller's thread to this Transaction and detach the thread from any former Transaction the thread may have been associated with.

leave

void leave()

Detach the caller's thread from this Transaction, but do not attach the thread to another Transaction.

begin

void begin()

Start a transaction. Calling begin multiple times on the same transaction object, without an intervening call to commit or abort, causes the exception TransactionInProgressException to be thrown on the second and subsequent calls. Operations executed before a transaction has been opened, or before reopening after a transaction is aborted or committed, have undefined results; these may throw a TransactionNotInProgressException exception.

isOpen

boolean isOpen()

Determine whether the transaction is open or not. A transaction is open if a call has been made to begin, but a subsequent call to either commit or abort has not been made.

Returns:

True if the transaction is open, otherwise false.

commit

void commit()

Commit and close the transaction. Calling commit commits to the database all persistent object modifications within the transaction and releases any locks held by the transaction. A persistent object modification is an update of any field of an existing persistent object, or an update or creation of a new named object in the database. If a persistent object modification results in a reference from an existing persistent object to a transient object, the transient object is moved to the database, and all references to it updated accordingly. Note that the act of moving a transient object to the database may create still more persistent references to transient objects, so its referents must be examined and moved as well. This process continues until the database contains no references to transient objects, a condition that is guaranteed as part of transaction commit. Committing a transaction does not remove from memory transient objects created during the transaction

abort

void abort()

Abort and close the transaction. Calling abort abandons all persistent object modifications and releases the associated locks. Aborting a transaction does not restore the state of modified transient objects

checkpoint

void checkpoint()

Commit the transaction, but reopen the transaction, retaining all locks. Calling checkpoint commits persistent object modifications made within the transaction since the last checkpoint to the database. The transaction retains all locks it held on those objects at the time the checkpoint was invoked.

lock

void lock(java.lang.Object obj,
          int lockMode)
          throws LockNotGrantedException

Upgrade the lock on the given object to the given lock mode. The call has no effect if the object's current lock is already at or above that level of lock mode.

Parameters:

obj - The object to acquire a lock on.

lockMode - The lock mode to acquire. The lock modes are READ, UPGRADE, and WRITE.

Throws:

LockNotGrantedException - Is thrown if the given lock mode could not be acquired.

tryLock

boolean tryLock(java.lang.Object obj,
                int lockMode)

Upgrade the lock on the given object to the given lock mode. Method tryLock is the same as lock except it returns a boolean indicating whether the lock was granted instead of generating an exception.

Parameters:

obj - The object to acquire a lock on.

lockMode - The lock mode to acquire. The lock modes are READ, UPGRADE, and WRITE.

Returns:

True if the lock has been acquired, otherwise false.