gistfile1.java

/*

  JDO Persistence Manager in Scala using blocks
  Sample below works with Google App Engine

  Sample usage:

   Persistence.manage { (pm) =>
     val message = new Message("message body here")
     pm.makePersistent(message)
   }


  If we did this the Java way it would look like this:

  public final class PMF {
      private static final PersistenceManagerFactory pmfInstance =
          JDOHelper.getPersistenceManagerFactory("transactions-optional");

      private PMF() {}

      public static PersistenceManagerFactory get() {
          return pmfInstance;
      }
  }

  This is how it would be used:

  Greeting greeting = new Greeting(user, content, date);

  PersistenceManager pm = PMF.get().getPersistenceManager();
  try {
    pm.makePersistent(greeting);
  } finally {
    pm.close();
  }
  
  The Scala implementation just seems a lot more DRY and a perfect use for blocks - in many
  cases a user will want to edit values inside the managed Persistent block before close is
  called. Blocks remove the ceremony that is involved with the try/finally block.

 */

import javax.jdo.{PersistenceManager, JDOHelper, PersistenceManagerFactory}

object Persistence {
  private val factory: PersistenceManagerFactory = JDOHelper.getPersistenceManagerFactory("transactions-optional")

  def manager = factory.getPersistenceManager

  def manage(persistenceClosure: PersistenceManager => Unit) = {
    val pm = manager
    try {
     persistenceClosure(pm)
    } finally {
      pm.close
    }
  }
}