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 Database and Database 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: getDatabase Query

Field Summary
static AccessModeDbLocked
Database lock access.
static AccessModeExclusive
Exclusive access.
static AccessModeReadOnly
Read only access.
static AccessModeShared
Shared access.
Method Summary
voidbegin()
Begin a new transaction.
voidclose()
Closes the database.
voidcommit()
Commits and closes the transaction.
voidcreate(Object object)
Creates a new object in persistent storage.
CacheManagergetCacheManager()
Get's the CacheManager instance.
ClassLoadergetClassLoader()
Returns the current ClassLoader if one has been set for this Database instance.
StringgetDatabaseName()
Return the name of the database
IdentitygetIdentity(Object object)
Returns the object's identity.
ConnectiongetJdbcConnection()
Gets the underlying JDBC connection.
OQLQuerygetNamedQuery(String name)
Creates an OQL query based upon a named query as defined in the mapping file. OQLQuery
OQLQuerygetOQLQuery()
Creates an OQL query with no statement. OQLQuery must be called before the query can be executed.
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.
booleanisLocked(Class cls, Object identity)
Returns true if the specified object is currently locked.
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, Object identity, AccessMode mode)

Load an object of the specified type and given identity.

Objectload(Class type, Object identity, Object object)

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.
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 AccessMode DbLocked
Database lock access. Used with queries and the 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 AccessMode Exclusive
Exclusive access. Used with queries and the 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 AccessMode ReadOnly
Read only access. Used with queries and the 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 AccessMode Shared
Shared access. Used with queries and the 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

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 TransactionAbortedException exception is thrown.

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

getCacheManager

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

Returns: the CacheManager-instance.

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

Returns: The database name.

getIdentity

public Identity getIdentity(Object object)
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.

getJdbcConnection

public Connection getJdbcConnection()
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.

getNamedQuery

public OQLQuery getNamedQuery(String name)
Creates an OQL query based upon a named query as defined in the mapping file. OQLQuery

Parameters: name Name of the (named) query to create.

Returns: An OQL query

Throws: PersistenceException

getOQLQuery

public OQLQuery getOQLQuery()
Creates an OQL query with no statement. OQLQuery 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: oql An OQL query statement

Returns: An OQL query

Throws: PersistenceException

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.

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

isClosed

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

Returns: True if the database is closed

isLocked

public boolean isLocked(Class cls, Object identity)
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.

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

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

public Object load(Class type, Object identity, AccessMode mode)

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

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

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

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

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.

Parameters: autoStore True if this feature should be enabled.

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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