org.exolab.castor.jdo

Interface Database

public interface Database

An open connection to the database. This object represents an open connection to the database that can be used to perform transactional operations on the database.

Database operations can only be performed in the context of a transaction. Client applications should begin and commit a transaction using the {@link #begin} and {@link #commit} methods. Server applications should use implicit transaction demaraction by the container or explicit transaction demarcation using javax.transaction.UserTransaction.

All objects queried and created during a transaction are persistent. Changes to persistent objects will be stored in the database when the transaction commits. Changes will not be stored if the transaction is rolled back or fails to commit.

Once the transaction has committed or rolled back, all persistent objects become transient. Opening a new transaction does not make these objects persistent.

For example:

 Database     db;
 Query        oql;
 QueryResults results;
 Product      prod;

 // Open a database and start a transaction
 db = jdo.getDatabase();
 db.begin();
 // Select all the products in a given group
 oql = db.getOQLQuery( "SELECT p FROM Product p WHERE group=$");
 oql.bind( groupId );
 results = oql.execute();
 while ( results.hasMore() ) {
   // A 25% mark down for each product and mark as sale
   prod = (Product) results.next();
   prod.markDown( 0.25 );
   prod.setOnSale( true );
 }
 // Commit all changes, close the database
 db.commit();
 db.close();
 

Version: $Revision: 1.1.1.1 $ $Date: 2003/03/03 07:08:06 $

Author: Assaf Arkin

See Also: JDO Query

Field Summary
static shortDbLocked
Database lock access.
static shortExclusive
Exclusive access.
static shortReadOnly
Read only access.
static shortShared
Shared access.
Method Summary
voidbegin()
Begin a new transaction.
voidcheckpoint()
voidclose()
Closes the database.
voidcommit()
Commits and closes the transaction.
voidcreate(Object object)
Creates a new object in persistent storage.
voiddeletePersistent(Object object)
ClassLoadergetClassLoader()
Returns the current ClassLoader if one has been set for this Database instance.
StringgetDatabaseName()
Return the name of the database
ObjectgetIdentity(Object object)
Returns the object's identity.
OQLQuerygetOQLQuery()
Creates an OQL query with no statement.
OQLQuerygetOQLQuery(String oql)
Creates an OQL query from the supplied statement.
QuerygetQuery()
Creates an empty query.
PersistenceInfoGroupgetScope()
booleanisActive()
Returns true if a transaction is currently active.
booleanisAutoStore()
Return if the current transaction is set to autoStore, it there is transaction active.
booleanisClosed()
Returns true if the database is closed.
booleanisPersistent(Object object)
Returns true if the object is persistent.
Objectload(Class type, Object identity)
Load an object of the specified type and given identity.
Objectload(Class type, Complex identity)
Load an object of the specified type and given identity which spans on more than one fields.
Objectload(Class type, Object identity, short accessMode)
Experimental

Load an object of the specified type and given identity.

Objectload(Class type, Complex identity, short accessMode)
Experimental

Load an object of the specified type and given identity.

Objectload(Class type, Object identity, Object object)
Experimental

Load an object of the specified type and given identity into a given instance of object.

voidlock(Object object)
Acquire a soft write lock on the object.
voidmakePersistent(Object object)
voidremove(Object object)
Removes the object from persistent storage.
voidrollback()
Rolls back and closes the transaction.
voidsetAutoStore(boolean autoStore)
True if autoStore is set on.
voidupdate(Object object)
Update a data object which is queried/loaded/created in another transaction.

Field Detail

DbLocked

public static final short DbLocked
Database lock access. Used with queries and the {@link #load} method to load objects with a database lock.

Database lock prevents two concurrent transactions from accessing the same record either through Castor or direct database access by acquiring a write lock in the select statement. Concurrent transactions will block until the lock is released at commit time.

When an object is first loaded in the transaction, it will be synchronized with the database and not populated from the cache. Dirty checking is not required.

Exclusive

public static final short Exclusive
Exclusive access. Used with queries and the {@link #load} method to load objects with exclusive access.

Exclusive access prevents two concurrent transactions from accessing the same record. In exclusive mode objects acquire a write lock, and concurrent transactions will block until the lock is released at commit time.

Dirty checking is enabled for all fields marked as such. When an object is first loaded in the transaction, it will be synchronized with the database and not populated from the cache.

ReadOnly

public static final short ReadOnly
Read only access. Used with queries and the {@link #load} method to load objects as read-only.

Read-only objects are not persistent and changes to these objects are not reflected in the database when the transaction commits.

Shared

public static final short Shared
Shared access. Used with queries and the {@link #load} method to load objects with shared access.

Shared access allows the same record to be accessed by two concurrent transactions, each with it's own view (object).

These objects acquire a read lock which escalated to a write lock when the transaction commits if the object has been modified. Dirty checking is enabled for all fields marked as such, and a cached copy is used to populate the object.

Method Detail

begin

public void begin()
Begin a new transaction. A transaction must be open in order to query and persist objects.

Throws: PersistenceException A transaction is already open on this database, or an error reported by the persistence engine

checkpoint

public void checkpoint()

Deprecated: Use {@link #commit} and {@link #rollback} instead; this method cannot be implemented properly with multiple type of locks and will not be supported in future versions of the API

close

public void close()
Closes the database. If a client transaction is in progress the transaction will be rolled back and an exception thrown. If an app-server transaction is in progress, the transaction will commit/rollback when triggered by the application server.

Throws: PersistenceException An error occured while attempting to close the database

commit

public void commit()
Commits and closes the transaction. All changes made to persistent objects during the transaction are made persistent; objects created during the transaction are made durable; and, objects removed during the transaction are removed from the database.

In other words, any modifications to any data objects which are queried/loaded/created/update to this database is automatically stored to the database and visible to subsequence transactions. (ie. update is solely used for long transaction support and should not be called for any data object queried/loaded/created in the this transaction.)

If the transaction cannot commit, the entire transaction rolls back and a {@link TransactionAbortedException} exception is thrown.

After this method returns, the transaction is closed and all persistent objects are transient. Using {@link #begin} to open a new transaction will not restore objects to their persistent stage.

Throws: TransactionNotInProgressException Method called while transaction is not in progress TransactionAbortedException The transaction cannot commit and has been rolled back

create

public void create(Object object)
Creates a new object in persistent storage. The object will be persisted only if the transaction commits.

If the object has an identity then duplicate identity check happens in this method, and the object is visible to queries in this transaction. If the identity is null, duplicate identity check occurs when the transaction completes and the object is not visible to queries until the transaction commits.

Parameters: object The object to create

Throws: TransactionNotInProgressException Method called while transaction is not in progress DuplicateIdentityException An object with this identity already exists in persistent storage ClassNotPersistenceCapableException The class is not persistent capable PersistenceException An error reported by the persistence engine

deletePersistent

public void deletePersistent(Object object)

Deprecated: See {@link #remove}

getClassLoader

public ClassLoader getClassLoader()
Returns the current ClassLoader if one has been set for this Database instance.

Returns: ClassLoader the current ClassLoader instance, null if no ClassLoader's instance has been explicitely set.

getDatabaseName

public String getDatabaseName()
Return the name of the database

getIdentity

public Object getIdentity(Object object)
Returns the object's identity. If the identity was determined when the object was created, or if the object was retrieved, that identity is returned. If the identity has been modified, this will not be reflected until the transaction commits. Null is returned if the identity is null, the object does not have any identity, or the object is not persistent.

Parameters: object The object

Returns: The object's identity, or null

getOQLQuery

public OQLQuery getOQLQuery()
Creates an OQL query with no statement. {@link OQLQuery#create} must be called before the query can be executed.

Returns: An OQL query

getOQLQuery

public OQLQuery getOQLQuery(String oql)
Creates an OQL query from the supplied statement.

Parameters: query An OQL query statement

Returns: An OQL query

Throws: QueryException The query syntax is invalid

getQuery

public Query getQuery()
Creates an empty query. The query must be created before it can be executed.

Returns: A query

getScope

public PersistenceInfoGroup getScope()

isActive

public boolean isActive()
Returns true if a transaction is currently active.

Returns: True if a transaction is active

isAutoStore

public boolean isAutoStore()
Return if the current transaction is set to autoStore, it there is transaction active. If there is no active transaction, return if the next transaction will be set to autoStore.

If autoStore is set on. AutoStore will create all reachable object if the object is not loaded from the transaction. If it is turn off, only dependent object will be created automatically.

isClosed

public boolean isClosed()
Returns true if the database is closed.

Returns: True if the database is closed

isPersistent

public boolean isPersistent(Object object)
Returns true if the object is persistent. An object is persistent if it was created or queried in this transaction. If the object was created or queried in another transaction, or there is no open transaction, this method returns null.

Parameters: object The object

Returns: True if persistent in this transaction

load

public Object load(Class type, Object identity)
Load an object of the specified type and given identity. Once loaded the object is persistent. Calling this method with the same identity in the same transaction will return the same object. This method is equivalent to a query that returns a single object. If the identity spans on more than one field, all of the identity fields can be wrapped in a Complex object.

Parameters: type The object's type identity The object's identity

Throws: ObjectNotFoundException No object of the given type and identity was found in persistent storage LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object TransactionNotInProgressException Method called while transaction is not in progress PersistenceException An error reported by the persistence engine

load

public Object load(Class type, Complex identity)
Load an object of the specified type and given identity which spans on more than one fields.

Parameters: type The object's type identity The object's identity

Throws: ObjectNotFoundException No object of the given type and identity was found in persistent storage LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object TransactionNotInProgressException Method called while transaction is not in progress PersistenceException An error reported by the persistence engine

load

public Object load(Class type, Object identity, short accessMode)
Experimental

Load an object of the specified type and given identity. Once loaded the object is persistent. Calling this method with the same identity in the same transaction will return the same object. This method is equivalent to a query that returns a single object.

Parameters: type The object's type identity The object's identity accessMode The access mode

Throws: ObjectNotFoundException No object of the given type and identity was found in persistent storage LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object TransactionNotInProgressException Method called while transaction is not in progress PersistenceException An error reported by the persistence engine

load

public Object load(Class type, Complex identity, short accessMode)
Experimental

Load an object of the specified type and given identity. Once loaded the object is persistent. Calling this method with the same identity in the same transaction will return the same object. This method is equivalent to a query that returns a single object. If the identity spans on more than one field, all of the identity fields can be wrapped in a Complex object.

Parameters: type The object's type identity The object's identity accessMode The access mode

Throws: ObjectNotFoundException No object of the given type and identity was found in persistent storage LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object TransactionNotInProgressException Method called while transaction is not in progress PersistenceException An error reported by the persistence engine

load

public Object load(Class type, Object identity, Object object)
Experimental

Load an object of the specified type and given identity into a given instance of object. Once loaded the object is persistent. Calling this method with the same identity in the same transaction will return the same object. This method is equivalent to a query that returns a single object. If the identity spans on more than one field, all of the identity fields can be wrapped in a Complex object.

Parameters: type The object's type identity The object's identity object The object instance to be loaded into

Throws: ObjectNotFoundException No object of the given type and identity was found in persistent storage LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object TransactionNotInProgressException Method called while transaction is not in progress PersistenceException An error reported by the persistence engine

lock

public void lock(Object object)
Acquire a soft write lock on the object. Read locks are implicitly available when the object is queried. A write lock is only granted for objects that are created or deleted or for objects loaded in exclusive mode - this method can obtain such a lock explicitly.

A soft lock is acquired in memory, not in the database. To acquire a lock in the database, use the locked access mode.

If the object already has a write lock in this transaction or a read lock in this transaction but no read lock in any other transaction, a write lock is obtained. If this object has a read lock in any other transaction this method will block until the other transaction will release its lock. If the timeout has elapsed or a deadlock has been detected, an exception will be thrown but the current lock will be retained.

Parameters: object The object to lock

Throws: TransactionNotInProgressException Method called while transaction is not in progress ObjectNotPersistentException The object has not been queried or created in this transaction LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object PersistenceException An error reported by the persistence engine

makePersistent

public void makePersistent(Object object)

Deprecated: See {@link #create}

remove

public void remove(Object object)
Removes the object from persistent storage. The deletion will take effect only if the transaction is committed, but the object is no longer visible to queries in the current transaction and locks for access from other transactions will block until this transaction completes.

Parameters: object The object to remove

Throws: TransactionNotInProgressException Method called while transaction is not in progress ObjectNotPersistentException The object has not been queried or created in this transaction LockNotGrantedException Timeout or deadlock occured attempting to acquire a lock on the object PersistenceException An error reported by the persistence engine

rollback

public void rollback()
Rolls back and closes the transaction. All changes made to persistent objects during the transaction are lost, objects created during the transaction are not made durable and objects removed during the transaction continue to exist.

Throws: TransactionNotInProgressException Method called while transaction is not in progress

setAutoStore

public void setAutoStore(boolean autoStore)
True if autoStore is set on.

This method should be called before begin().

If autoStore is set, and db.create( theDataObject ) is called, Castor will create theDataObject, and create each object that does not exist in the transaction and reachable from theDataObject.

If db.update( theDataObject ), and theDataObject is loaded/queuied/created in a previous transaction, Castor will let theDataObject, and all reachable object from theDataObject, participate in the current transaction.

If autoStore is not set, Castor will only create/update/store dependent object, and related objects must be created/update explicitly.

update

public void update(Object object)
Update a data object which is queried/loaded/created in another transaction. This method is used only for long transaction support. Calling this method for data object queried/loaded/created in the same transaction results in Exception.

For example, the data object may be sent to a client application and dispayed to a user. After that the objects is being modified in the client application, the object returns back and is update to the database in the second transaction.

See Long Transaction on Castor website.

Parameters: object The object to create

Throws: TransactionNotInProgressException Method called while transaction is not in progress ClassNotPersistenceCapableException The class is not persistent capable PersistenceException An error reported by the persistence engine

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