Thursday, March 01, 2007
New Adventures in JPA with WTP 2.0M5
The data migration was fairly easy to do, especially now that I've done it before with accounts and articles. Unfortunately when I went to map the new tables to Java classes, Dali pulled its disappearing act again. I don't recall whether I mentioned this here before, but Dali 0.5 has a tendency to just disappear from Eclipse for no apparent reason. It fails to load, silently of course. Why log an error, when you can silently fail?
Luckly, though, Dali has been integrated into the Eclipse Web Tools Project (WTP) version 2.0 and there's a reasonably functional version of it in 2.0M5. Of course the problem with milestone builds is that they tend to lack any documentation whatsoever, so you're kind of on your own.
This became immediately frustrating. When I opened the JPA perspective for the first time, I couldn't add a connection. The drivers list was empty. It turns out you have to first populate a connection via WTP from the Window/Properties/Connectivity/Driver Definitions menu. It was easy to add a definition to connect to my PostgreSQL 8.1 database.
(At some point during this process, there was a magnitude 4.2 earthquake about 30 miles away on the Calaveras fault that shook the house and made a good loud noise. It was a little mild shake followed by one nice big jolt and then some rolling. All told it lasted maybe 5 seconds and was probably the most startling jolt I've felt since I've lived here, with the exception of the magnitude 6.5 earthquake near Paso Robles on December 22, 2003 that caused the lights in my office in San Jose to sway and nearly sent me scrambling under my desk. That time I had about 30 seconds of warning from my coworker in Salinas who I was talking to on the phone at the time.)
(As a side note, I got tired of poking holes in my host machine's firewall, adding the IP to PostgreSQL's allow pg_hba.conf and reloading PostgreSQL every time my dynamic IP changed at home, so I did the most reasonable thing: I added an SSH tunnel from my local machine's loopback to my remote machine's loopback on port 5432. Now I just connect to localhost for PostgreSQL, and it magically works. Using the loopback address on both ends mitigates potential security problems from creating such a tunnel.)
Finally I was able to add a database, but nothing worked with JPA. This is apparently because the necessary settings and natures defined for JPA with earlier versions of Dali are outdated. To make matters worse, they did not create a context or other menu (yet) to add JPA to the current project as they had with Dali 0.5. So I did what any impatient geek would do: I created a new JPA project, and then manually copied the missing natures in .project and missing files in .settings to my existing project. This seems to have done the trick.
The next hurdle is that the Java Persistence/Generate Entities... context menu is broken. First it was popping up a dialog box asking for the connection and schema to use. I could select my connection, but the drop down for schemas was empty. Entering the schema name manually was fruitless. The Next and Finish buttons remained disabled.
So then, having experienced weirdness related to missing configuration before, I went on the hunt again. This time I found the JPA settings in the project properties. Here I could select a connection, so I did. While this did change the behaviour of Generate Entities, it was for the worse: now the menu does nothing. Silent failure. I have reported the problem on the Eclipse site and asked for advice, but for now this has me stuck. It's time for bed anyway.
I guess this will help you.
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