GWT-Objectify : basic - gwt

Question

I've been through a few documentations, but am not able to communicate to the datastore yet...can anyone give me a sample project/code of objectify used in GWT web app(I use eclipse)...just a simple 'put' and 'get' action using RPC should do...or, atleast tell me how its done

Answer 1

Easiest way to understand how to make objectify work is to repeat all steps described in this article from David's Chandler blog. Whole blog is a pretty much must read if you interested in GWT, GAE(Java), gwt-presenter, gin\guice,etc. There you will find working example, but anyway here i'll show a slighly advanced example.
In package shared define your entity/model:
import javax.persistence.Embedded;
import javax.persistence.Id;
import com.google.gwt.user.client.rpc.IsSerializable;
import com.googlecode.objectify.Key;
import com.googlecode.objectify.annotation.Entity;
import com.googlecode.objectify.annotation.Unindexed;
#Entity
public class MyEntry implements IsSerializable {
// Objectify auto-generates Long IDs just like JDO / JPA
#Id private Long id;
#Unindexed private String text = "";
#Embedded private Time start;
// empty constructor for serialization
public MyEntry () {
}
public MyEntry (Time start, String text) {
super();
this.text = tText;
this.start = start;
}
/*constructors,getters,setters...*/
}
Time class (also shared package) contains just one field msecs:
#Entity
public class Time implements IsSerializable, Comparable<Time> {
protected int msecs = -1;
//rest of code like in MyEntry
}
Copy class ObjectifyDao from link above to your server.dao package. And then make DAO class specifically for MyEntry -- MyEntryDAO:
package com.myapp.server.dao;
import java.util.logging.Logger;
import com.googlecode.objectify.ObjectifyService;
import com.myapp.shared.MyEntryDao;
public class MyEntryDao extends ObjectifyDao<MyEntry>
{
private static final Logger LOG = Logger.getLogger(MyEntryDao.class.getName());
static
{
ObjectifyService.register(MyEntry.class);
}
public MyEntryDao()
{
super(MyEntry.class);
}
}
Finally we can make requests to database(server package):
public class FinallyDownloadingEntriesServlet extends HttpServlet {
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws
ServletException, IOException {
resp.setCharacterEncoding("UTF-8");
resp.setContentType("text/plain");
//more code...
resp.setHeader("Content-Disposition", "attachment; filename=\""+"MyFileName"+".txt\";");
try {
MyEntryDao = new MyEntryDao();
/*query to get all MyEntries from datastore sorted by start Time*/
ArrayList<MyEntry> entries = (ArrayList<MyEntry>) dao.ofy().query(MyEntry.class).order("start.msecs").list();
PrintWriter out = resp.getWriter();
int i = 0;
for (MyEntry entry : entries) {
++i;
out.println(i);
out.println(entry.getStart() + entry.getText());
out.println();
}
} finally {
//catching exceptions
}
}