You are viewing a plain text version of this content. The canonical link for it is here.
Posted to jdo-commits@db.apache.org by an...@apache.org on 2007/10/02 15:02:49 UTC
svn commit: r581220 - in /db/jdo/site/xdocs/tutorials: ./ replication.xml
Author: andyj
Date: Tue Oct 2 06:02:49 2007
New Revision: 581220
URL: http://svn.apache.org/viewvc?rev=581220&view=rev
Log:
JDO-537 Upgrade site to use Maven1 "site". Start process of merging in JPOX JDO docs
Added:
db/jdo/site/xdocs/tutorials/
db/jdo/site/xdocs/tutorials/replication.xml
Added: db/jdo/site/xdocs/tutorials/replication.xml
URL: http://svn.apache.org/viewvc/db/jdo/site/xdocs/tutorials/replication.xml?rev=581220&view=auto
==============================================================================
--- db/jdo/site/xdocs/tutorials/replication.xml (added)
+++ db/jdo/site/xdocs/tutorials/replication.xml Tue Oct 2 06:02:49 2007
@@ -0,0 +1,148 @@
+<?xml version="1.0" encoding="iso-8859-1"?>
+<document>
+ <properties>
+ <title>Tutorial : Datastore Replication</title>
+ </properties>
+
+ <body>
+ <section name="Data Replication">
+ <p>
+ There are times when you need to replicate data between datastores. In many cases datastores themselves provide a means of doing this, however if you want to avoid using datastore-specific functionality you can utilise JDO to perform this task.
+ JDO2 allows replication by use of detach/attach functionality.
+ We demonstrate this with an example
+ </p>
+ <source>
+public class ElementHolder
+{
+ long id;
+ private Set elements = new HashSet();
+
+ ...
+}
+
+public class Element
+{
+ String name;
+
+ ...
+}
+
+public class SubElement extends Element
+{
+ double value;
+
+ ...
+}</source>
+ <p>
+ so we have a 1-N unidirectional (Set) relation, and we define the metadata like this
+ </p>
+ <source><![CDATA[
+<jdo>
+ <package name="org.apache.jdo.test">
+ <class name="ElementHolder" identity-type="application" detachable="true">
+ <inheritance strategy="new-table"/>
+ <field name="id" primary-key="true"/>
+ <field name="elements" persistence-modifier="persistent">
+ <collection element-type="Element"/>
+ <join/>
+ </field>
+ </class>
+
+ <class name="Element" identity-type="application" detachable="true">
+ <inheritance strategy="new-table"/>
+ <field name="name" primary-key="true"/>
+ </class>
+
+ <class name="SubElement">
+ <inheritance strategy="new-table"/>
+ <field name="value"/>
+ </class>
+ </package>
+</jdo>]]></source>
+ <p>
+ and so in our application we create some objects in <i>datastore1</i>, like this
+ </p>
+ <source>
+PersistenceManagerFactory pmf1 = JDOHelper.getPersistenceManagerFactory("jdo.1.properties");
+PersistenceManager pm1 = pmf1.getPersistenceManager();
+Transaction tx1 = pm1.currentTransaction();
+Object holderId = null;
+try
+{
+ tx1.begin();
+
+ ElementHolder holder = new ElementHolder(101);
+ holder.addElement(new Element("First Element"));
+ holder.addElement(new Element("Second Element"));
+ holder.addElement(new SubElement("First Inherited Element"));
+ holder.addElement(new SubElement("Second Inherited Element"));
+ pm1.makePersistent(holder);
+
+ tx1.commit();
+ holderId = JDOHelper.getObjectId(holder);
+}
+finally
+{
+ if (tx1.isActive())
+ {
+ tx1.rollback();
+ }
+ pm1.close();
+}</source>
+ <p>
+ and now we want to replicate these objects into <i>datastore2</i>, so we detach them from <i>datastore1</i>
+ and attach them to <i>datastore2</i>, like this
+ </p>
+ <source>
+// Detach the objects from "datastore1"
+ElementHolder detachedHolder = null;
+pm1 = pmf1.getPersistenceManager();
+tx1 = pm1.currentTransaction();
+try
+{
+ pm1.getFetchPlan().setGroups(new String[] {FetchPlan.DEFAULT, FetchPlan.ALL});
+ pm1.getFetchPlan().setMaxFetchDepth(-1);
+
+ tx1.begin();
+
+ ElementHolder holder = (ElementHolder) pm1.getObjectById(holderID);
+ detachedHolder = (ElementHolder) pm1.detachCopy(holder);
+
+ tx1.commit();
+}
+finally
+{
+ if (tx1.isActive())
+ {
+ tx1.rollback();
+ }
+ pm1.close();
+}
+
+// Attach the objects to datastore2
+PersistenceManagerFactory pmf2 = JDOHelper.getPersistenceManagerFactory("jdo.2.properties");
+PersistenceManager pm2 = pmf2.getPersistenceManager();
+Transaction tx2 = pm2.currentTransaction();
+try
+{
+ tx2.begin();
+
+ pm2.makePersistent(detachedHolder);
+
+ tx2.commit();
+}
+finally
+{
+ if (tx2.isActive())
+ {
+ tx2.rollback();
+ }
+ pm2.close();
+}</source>
+ <p>
+ These objects are now replicated into <i>datastore2</i>.
+ Clearly you can extend this basic idea and replicate large amounts of data.
+ </p>
+ </section>
+ </body>
+</document>