org.exolab.castor.jdo

Interface Database

All Known Implementing Classes:

AbstractDatabaseImpl, GlobalDatabaseImpl, LocalDatabaseImpl

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 begin() and 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: 6075 $ $Date: 2006-03-16 16:04:24 -0700 (Thu, 16 Mar 2006) $

Author:

Assaf Arkin

See Also:

JDOManager.getDatabase(), Query

Field Summary

Fields

Modifier and Type	Field and Description
static AccessMode	DbLocked Database lock access.
static AccessMode	Exclusive Exclusive access.
static AccessMode	ReadOnly Read only access.
static AccessMode	Shared Shared access.

Method Summary

Modifier and Type	Method and Description
void	begin() Begin a new transaction.
void	close() Closes the database.
void	commit() Commits and closes the transaction.
void	create(java.lang.Object object) Creates a new object in persistent storage.
CacheManager	getCacheManager() Get's the CacheManager instance.
java.lang.ClassLoader	getClassLoader() Returns the current ClassLoader if one has been set for this Database instance.
java.lang.String	getDatabaseName() Return the name of the database
Identity	getIdentity(java.lang.Object object) Returns the object's identity.
java.sql.Connection	getJdbcConnection() Gets the underlying JDBC connection.
OQLQuery	getNamedQuery(java.lang.String name) Creates an OQL query based upon a named query as defined in the mapping file.
OQLQuery	getOQLQuery() Creates an OQL query with no statement.
OQLQuery	getOQLQuery(java.lang.String oql) Creates an OQL query from the supplied statement.
Query	getQuery() Creates an empty query.
PersistenceInfoGroup	getScope()
boolean	isActive() Returns true if a transaction is currently active.
boolean	isAutoStore() Return if the current transaction is set to autoStore, it there is transaction active.
boolean	isClosed() Returns true if the database is closed.
boolean	isLocked(java.lang.Class cls, java.lang.Object identity) Returns true if the specified object is currently locked.
boolean	isPersistent(java.lang.Object object) Returns true if the object is persistent.
java.lang.Object	load(java.lang.Class type, java.lang.Object identity) Load an object of the specified type and given identity.
java.lang.Object	load(java.lang.Class type, java.lang.Object identity, AccessMode mode) Load an object of the specified type and given identity.
java.lang.Object	load(java.lang.Class type, java.lang.Object identity, java.lang.Object object) Load an object of the specified type and given identity into a given instance of object.
void	lock(java.lang.Object object) Acquire a soft write lock on the object.
void	remove(java.lang.Object object) Removes the object from persistent storage.
void	rollback() Rolls back and closes the transaction.
void	setAutoStore(boolean autoStore) True if autoStore is set on.
void	update(java.lang.Object object) Update a data object which is queried/loaded/created in another transaction.

Field Detail

ReadOnly

static final AccessMode ReadOnly

Read only access. Used with queries and the load(Class,Object) 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

static final AccessMode Shared

Shared access. Used with queries and the load(Class,Object) 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.

Exclusive

static final AccessMode Exclusive

Exclusive access. Used with queries and the load(Class,Object) 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.

DbLocked

static final AccessMode DbLocked

Database lock access. Used with queries and the load(Class,Object) 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.

Method Detail

getOQLQuery

OQLQuery getOQLQuery()

Creates an OQL query with no statement. OQLQuery.create(java.lang.String) must be called before the query can be executed.

Returns:

An OQL query

getOQLQuery

OQLQuery getOQLQuery(java.lang.String oql)
              throws PersistenceException

Creates an OQL query from the supplied statement.

Parameters:

oql - An OQL query statement

Returns:

An OQL query

Throws:

PersistenceException

getQuery

Query getQuery()

Creates an empty query. The query must be created before it can be executed.

Returns:

A query

getNamedQuery

OQLQuery getNamedQuery(java.lang.String name)
                throws PersistenceException

Creates an OQL query based upon a named query as defined in the mapping file. OQLQuery.create(java.lang.String)

Parameters:

name - Name of the (named) query to create.

Returns:

An OQL query

Throws:

PersistenceException

getScope

PersistenceInfoGroup getScope()

getDatabaseName

java.lang.String getDatabaseName()

Return the name of the database

Returns:

The database name.

load

java.lang.Object load(java.lang.Class type,
                      java.lang.Object identity)
               throws TransactionNotInProgressException,
                      ObjectNotFoundException,
                      LockNotGrantedException,
                      PersistenceException

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

Returns:

The object instance.

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

java.lang.Object load(java.lang.Class type,
                      java.lang.Object identity,
                      AccessMode mode)
               throws TransactionNotInProgressException,
                      ObjectNotFoundException,
                      LockNotGrantedException,
                      PersistenceException

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

mode - The access mode

Returns:

The object instance.

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

java.lang.Object load(java.lang.Class type,
                      java.lang.Object identity,
                      java.lang.Object object)
               throws ObjectNotFoundException,
                      LockNotGrantedException,
                      TransactionNotInProgressException,
                      PersistenceException

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

Returns:

The object instance.

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

create

void create(java.lang.Object object)
     throws ClassNotPersistenceCapableException,
            DuplicateIdentityException,
            TransactionNotInProgressException,
            PersistenceException

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

remove

void remove(java.lang.Object object)
     throws ObjectNotPersistentException,
            LockNotGrantedException,
            TransactionNotInProgressException,
            PersistenceException

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

update

void update(java.lang.Object object)
     throws ClassNotPersistenceCapableException,
            TransactionNotInProgressException,
            PersistenceException

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

lock

void lock(java.lang.Object object)
   throws LockNotGrantedException,
          ObjectNotPersistentException,
          TransactionNotInProgressException,
          PersistenceException

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

begin

void begin()
    throws PersistenceException

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

isAutoStore

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.

Returns:

True if the current transaction is set to 'autoStore'.

setAutoStore

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.

Parameters:

autoStore - True if this feature should be enabled.

commit

void commit()
     throws TransactionNotInProgressException,
            TransactionAbortedException

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 TransactionAbortedException exception is thrown.

After this method returns, the transaction is closed and all persistent objects are transient. Using 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

rollback

void rollback()
       throws TransactionNotInProgressException

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

isActive

boolean isActive()

Returns true if a transaction is currently active.

Returns:

True if a transaction is active

isClosed

boolean isClosed()

Returns true if the database is closed.

Returns:

True if the database is closed

isLocked

boolean isLocked(java.lang.Class cls,
                 java.lang.Object identity)
          throws PersistenceException

Returns true if the specified object is currently locked.

Parameters:

cls - Class instance.

identity - Object identity.

Returns:

True if the object specified is locked; false otherwise.

Throws:

PersistenceException

close

void close()
    throws PersistenceException

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

isPersistent

boolean isPersistent(java.lang.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

getIdentity

Identity getIdentity(java.lang.Object object)
              throws PersistenceException

Returns the object's identity. The identity will be determined by calling the getters of the fields defined as identities in the mapping. If a mapping for the objects class could not be found a ClassNotPersistenceCapableException will be thrown. Null is only returned if the objects identity is null. It is not required to have an active transaction when using this method.

Note: Prior to 0.9.9.1 release of castor the identity could only be determined if the object took part in the transaction. If this was not the case, the previous implementation also returned null.

Parameters:

object - The object.

Returns:

The object's identity, or null.

Throws:

PersistenceException - The class is not persistent capable.

getClassLoader

java.lang.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.

getCacheManager

CacheManager getCacheManager()

Get's the CacheManager instance. Call getCacheManager for every Database-instances.

Returns:

the CacheManager-instance.

getJdbcConnection

java.sql.Connection getJdbcConnection()
                               throws PersistenceException

Gets the underlying JDBC connection. This is for advanced use only. Please make sure that you never close this Connection instance, as it will be closed by Castor.

Returns:

the underlying JDBC connection, if present; otherwise null

Throws:

PersistenceException - If the underlying JDBC connection cannot be obtained.