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Date: Wed, 18 Mar 2009 17:53:30 -0700
From: Craig L Russell <Craig.Russell@Sun.COM>
Subject: If you're not interested in Java and MySQL Cluster,
 you can stop reading now...
Sender: Craig.Russell@Sun.COM
To: Incubator <general@incubator.apache.org>
Message-id: <03C5B1FC-AF95-4046-A795-A5CEC52DC743@SUN.com>
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I'm working (day job!) on a Java interface to the MySQL Cluster =20
database (a.k.a. NDB). NDB is a high performance, high availability =20
database used mostly in telecommunications applications. It can be the =20=

backing store for a MySQL server (accessed via any of the MySQL client =20=

APIs such as ODBC, JDBC) or can be used directly via primitive C++ or =20=

Java APIs.

What I've been developing is a high performance, easy-to-use Java =20
interface to NDB that bypasses the MySQL Server and instead goes =20
directly to the native NDB API. I've used a Domain Object Model =20
similar to Hibernate, JDO, and JPA.

I'd like to work on this in Apache and would like to discuss the =20
opportunities with folks at ApacheCon. If this looks interesting, =20
please let me know. I'll post a proposal to the incubator wiki if =20
there is positive feedback.

All work is done through a Session instance, which is the primary =20
application interface between the user and the database.
The user acquires a Session instance from a SessionFactory, which in =20
turn is obtained via Services lookup. The factory is configured via =20
Properties, such as:
com.mysql.clusterj.connectstring=3D127.0.0.1:9311
com.mysql.clusterj.mysqld=3Dlocalhost
com.mysql.clusterj.username=3Droot
com.mysql.clusterj.password=3D
com.mysql.clusterj.testDatabase=3Dtest
The Session interface provides methods for insert, delete, query, and =20=

update.
A separate Transaction interface provides methods for transaction =20
completion. The Transaction provides isActive(), begin(), commit(), =20
rollback(), setRollbackOnly(), and getRollbackOnly() methods.
Two modes of operation are implemented: autocommit on/off.
	=95 With autocommit off:
		=95 when a mutating operation is invoked on the Session, =
the =20
Transaction must be active, or an exception is thrown; and
		=95 when a non-mutating operation is invoked when a =
Transaction is not =20
active, a transaction is begun and committed for the purpose of =20
executing the operation.
	=95 With autocommit on:
		=95 when a mutating operation is invoked on the Session, =
the =20
Transaction is begun and committed for the operation; and
		=95 when a non-mutating operation is invoked, a =
transaction is begun =20
and committed for the purpose of executing the operation.

Deferred operation is proposed. By setting the flag =20
com.mysql.clusterj.defer.changes, mutating operations are deferred =20
until the Transaction is committed or the state is flushed via =20
Session.flush(). With defer changes, find() operations return a proxy =20=

instance whose persistent properties are not initialized until the =20
user asks for one of them. Inserted instances are not actually sent to =20=

the back end until the session is flushed. Deleted instances are not =20
deleted until the session is flushed. Queries return a Results =20
instance that is not instantiated until the user asks for a property =20
of an instance.

For ease of use, users can define JavaBeans-pattern interfaces to =20
represent data, with annotations to declare database metadata:
  @PersistenceCapable(table=3D"t_basic")
interface Employee {
@PrimaryKey
int getId();
void setId(int id);
String getName();
void setName(String name);
}
The Session.newInstance(Class cls) is a factory for instances that =20
implement the user interface as well as a high-performance data access =20=

path for the implementation. For JPA/JDO StorageManager, the high-=20
performance data access path is used.


// Sample code to create a SessionFactory from a properties instance
     protected void createSessionFactory() {
         loadProperties();
         if (sessionFactory =3D=3D null) {
             sessionFactory =3D ClusterJHelper.getSessionFactory(props);
         }
         loadSchema();
     }

// Sample code to delete and create instances

     public void localSetUp() {
         createSessionFactory();
         session =3D sessionFactory.getSession();
         createEmployeeInstances(NUMBER_TO_INSERT);
         tx =3D session.currentTransaction();
         int count =3D 0;
         for (int i =3D 0; i < NUMBER_TO_INSERT; ++i) {
             tx.begin();
             session.deletePersistent(employees.get(i));
             try {
                 tx.commit();
                 ++count;
             } catch (Exception ex) {
                 // ignore exceptions -- might not be any instances to =20=

delete
             }
         }
         addTearDownClasses(Employee.class);
//        System.out.println("Deleted " + count + " instances.");
     }

     public void testInsert() {
         tx =3D session.currentTransaction();
         tx.begin();

         for (int i =3D 0; i < NUMBER_TO_INSERT; ++i) {
             // must be done with an active transaction
             session.makePersistent(employees.get(i));
         }

         tx.commit();
     }
}

// Sample query code
     public void primaryKeyGreaterThanQuery() {

         tx.begin();
         // QueryBuilder is the sessionFactory for queries
         QueryBuilder builder =3D session.getQueryBuilder();
         // DomainObject is the main interface
         DomainObject dobj =3D =20
builder.createQueryDefinition(Employee.class);

         // parameter name
         PredicateOperand param =3D dobj.param("id");
         // property name
         PredicateOperand column =3D dobj.get("id");
         // compare the column with the parameter
         Predicate compare =3D column.greaterThan(param);
         // set the where clause into the query
         dobj.where(compare);
         // create a query instance
         Query query =3D session.createQuery(dobj);

         // set the parameter values
         query.setParameter("id", 6);
         // get the results
         List<Employee> results =3D query.getResultList();
         // consistency check the results
         consistencyCheck(results);
         // verify we got the right instances
         Set<Integer> expected =3D new HashSet<Integer>();
         expected.add(7);
         expected.add(8);
         expected.add(9);
         Set<Integer> actual =3D new HashSet<Integer>();
         for (Employee emp: results) {
             actual.add(emp.getId());
         }
         errorIfNotEqual("Wrong employee ids returned from query: ",
                 expected, actual);
         tx.commit();
     }

Craig L Russell
Architect, Sun Java Enterprise System http://db.apache.org/jdo
408 276-5638 mailto:Craig.Russell@sun.com
P.S. A good JDO? O, Gasp!


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