Package org.exolab.castor.jdo

The Java Data Objects API

Version:

$Revision: 6216 $ $Date: 2005-04-21 14:21:10 -0600 (Thu, 21 Apr 2005) $

Author:

Assaf Arkin

The class JDOManager provides the Castor JDO engine used for obtaining a database connection. A JDO object is constructed with the name of a database and other properties, and getDatabase is used to obtain a new database connection.

The class Database 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.

The class OQLQuery is obtained from the database and used to construct and execute a query on that database. All query operations are bound to the database transaction.

The following example opens a connection to the database 'mydb' configured from the configuration file 'database.xml', retrieves all the products in the specified groups and marks them down with a 25% discount and on-sale status.

  JDOManager   jdo;
  Database     db;
  Query        oql;
  QueryResults results;

  // Define a new database source
  JDOManager.loadConfiguration ("jdo-conf.xml");
  JDOManager jdo = JDOManager.createInstance ( "mydb" );

  // Open a new database, begin a transaction
  db = jdo.getDatabase();
  db.begin();

  // Select all the products in a given group
  oql = db.getQuery( "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();
    

A CacheManager instance can be obtained by issuing the following code:

This instance can subsequently be used to selectively clear the Castor performance cache. Use one of the CacheManager.expireCache() methods.