Class COM.odi.odmg.Transaction

java.lang.Object
   |
   +----COM.odi.odmg.Transaction

public final class Transaction
extends Object

The way that ODMG uses a transaction is similar to the way that ObjectStore uses a transaction. There are methods for beginning, committing, and aborting the transaction. In addition, there are methods for joining the current ODMG transaction to the current thread, and detaching the current thread from this transaction. With these methods, ODMG transactions are like ObjectStore sessions. An ODMG transaction can be associated with several threads and multiple open databases.

However, ODMG transactions are different from ObjectStore transactions in that you can start and commit or abort the same ODMG transaction multiple times.

See Also:: Transaction

READ: Read lock on an object.
UPGRADE: Upgrade lock on an object when upgrading from a read lock to a write lock.
WRITE: Write lock on an object.

Transaction(): Instantiates a transaction on the current host, but does not start it yet.

abort(): Aborts the transaction and undoes any changes to the database that were made during the transaction.
begin(): Starts this transaction.
checkpoint(): Commits the transaction and reopens it without retaining locks.
commit(): Commits a transaction.
current(): Obtains the transaction associated with this thread.
isOpen(): Indicates whether or not this transaction is in progress.
join(): Joins this transaction to the current thread.
leave(): Detaches this transaction from the current thread.
lock(Object, int): Locks an object with the specified mode.

READ

  public final static int READ

Read lock on an object.

UPGRADE

  public final static int UPGRADE

Upgrade lock on an object when upgrading from a read lock to a write lock.

WRITE

  public final static int WRITE

Write lock on an object.

Transaction

  public Transaction()

Instantiates a transaction on the current host, but does not start it yet. A call to Transaction.begin() starts the transaction. An application can start and commit or abort the same instance of an ODMG transaction multiple times. This public constructor is necessary to conform with the ODMG API. The current thread is associated with this transaction.

Instantiation of a new transaction associates the current thread with the new instance of Transaction.

join

  public void join()

Joins this transaction to the current thread.

leave

  public void leave()

Detaches this transaction from the current thread. Does not attach another transaction to this thread.

current

  public static Transaction current()

Obtains the transaction associated with this thread.

Returns:: The transaction associated with this thread. If there is no transaction associated with the current thread, returns null.

begin

  public void begin()

Starts this transaction.

Throws: ObjectStoreException: If this transaction is not associated with any threads.
Throws: TransactionInProgressException: If this transaction has already been started.
See Also:: begin

isOpen

  public boolean isOpen()

Indicates whether or not this transaction is in progress. A call to Transaction.begin() starts the transaction.

Returns:: Returns true if this transaction is in progress, and false otherwise.

commit

  public void commit()

Commits a transaction.

Throws: ObjectNotPersistenceCapableException: If ObjectStore reaches an object while it is performing transitive persistence and that object is not persistence-capable.
Throws: ObjectStoreException: If there are no threads associated with this transaction.
Throws: TransactionNotInProgressException: If this transaction is not in progress.
See Also:: commit

abort

  public void abort()

Aborts the transaction and undoes any changes to the database that were made during the transaction.

Throws: ObjectStoreException: If there are no threads associated with this transaction.
Throws: TransactionNotInProgressException: If this transaction is not in progress.
See Also:: abort

checkpoint

  public void checkpoint()

Commits the transaction and reopens it without retaining locks. The ODMG Transaction.checkpoint() method retains locks from the committed transaction and reopens the transaction with the retained locks.

Throws: ObjectNotPersistenceCapableException: If ObjectStore reaches an object while it is performing transitive persistence and that object is not persistence-capable.
Throws: ObjectStoreException: If there are no threads associated with this transaction.
Throws: TransactionNotInProgressException: If this transaction is not in progress.

lock

  public void lock(Object obj,
                   int mode)

Locks an object with the specified mode. Currently, the UPGRADE mode does not have any meaning.

Parameters:: obj - The object to lock with the specified mode.; mode - The mode for locking this object, either READ or WRITE.
Throws: DatabaseNotFoundException: If the object was accessed through a cross-database reference to a database that is not found.
Throws: DatabaseClosedException: If the database that contains the object is not open.
Throws: ObjectException: If the object being locked is a stale object.
Throws: ObjectNotFoundException: If the object was destroyed, or its segment was destroyed.
Throws: ObjectNotPersistenceCapableException: If the object is not persistence-capable.
Throws: TransactionNotInProgressException: If this transaction is not in progress.