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From "Phill Moran" <pjmo...@rogers.com>
Subject RE: the pain of post processing bytecode (another beg for a simple reflection/cglib alternative like hibernate)
Date Fri, 18 May 2007 13:31:31 GMT
Let's also keep in mind that hibernate, although open source, is not public
standards based. This will drive some traffic towards JPA. Also as David pointed
out there is some cost to starting with any persistence framework (or really any
framework) so total plug and play for no time I think is an unattainable goal.

Phill

-----Original Message-----
From: David Ezzio [mailto:dezzio@bea.com] 
Sent: May 18, 2007 8:07 AM
To: open-jpa-dev@incubator.apache.org
Subject: Re: the pain of post processing bytecode (another beg for a simple
reflection/cglib alternative like hibernate)

Hi Marc,

The goal of drop-in and play functionality is wonderful, but I doubt that the
modest proposals thus far will achieve it.

Given that the JPA spec specifies only the EJB-3 configuration, I don't see how
we can achieve drop-in and play compatibility with application development
environments configured for any arbitrary JPA implementaion.

At one point, I had code examples working with every known implementation of
JDO.  Even after I had a half dozen implementations under my belt, it still took
a day or two to get the next implementation working with a sample application of
my own choosing.  I'm guessing that the effort required hasn't changed for JPA
implementations.

Also, I'm incline to doubt that vendors (even open source vendors) see it as in
their interest to make it easier for users to switch.  Reducing switching costs
to zero is an interesting goal, but I'm not sure how much value is there.

Perhaps our goal is more modest, just to make it easier for Hibernate users to
switch to OpenJPA.  Since Hibernate is more popular than OpenJPA, there's some
real value for us in that.

Best wishes,

David



Marc Prud'hommeaux wrote:
> 
> On May 17, 2007, at 5:31 PM, David Ezzio wrote:
> 
>> I think that the issues raised are best solved with tools, 
>> documentation, and examples.
>>
>> Of course, if one has been coding to Hibernate for years, it's 
>> unlikely that any combination of tools, documentation, and examples 
>> will make OpenJPA easier to use for that person, but that's not the standard.
> 
> Sure it will. If you are using one JPA implementation, be it 
> Hibernate, Toplink, or anything else, and you want to "drop in" 
> OpenJPA to test it out and see what the performance difference is, if 
> it doesn't work immediately, you are likely to walk away.
> 
> I think that easing the process for someone already familiar with JPA 
> to get started with OpenJPA without having to pour through 
> documentation about build-time tools or runtime agent flags is a 
> supremely useful project, especially at this point where we are on the 
> brink of graduation and will soon be getting a lot more attention.
> 
> 
>> Another important point, in my view, is to make sure the tests run as 
>> well on Windows (without cygwin!) as they do on Linux, Unix, and OS/X.
>> For example, using File.separator to construct resource path names 
>> works great on everything but Windows.
> 
> This seems orthogonal to the issue of easing OpenJPA's bytecode 
> enhancement process. If you find cases where we are relying on 
> hardcoded UNIX paths, these are obviously bugs and should be handled 
> by creating JIRA issues.
> 
> 
> 
>> David
>>
>> Marc Prud'hommeaux wrote:
>>>
>>> I think this is a very worthwhile project. James and a few others 
>>> excoriated me about this issue over beers after JavaOne last week, 
>>> and, while the bruises from their rhetorical assault are still 
>>> healing, their observations about the comparative "out of the box" 
>>> ease of use OpenJPA compared to other systems definitely bears attention.
>>>
>>> As Patrick mentioned, we aren't too far away from being able to use 
>>> a dynamic subclassing approach.
>>>
>>> Another option I've been thinking about recently is that in JDK 1.6, 
>>> you can dynamically attach an agent at runtime to your own JVM 
>>> (using an implementation-specific mechanism), and using the provided 
>>> Instrumentation, you can redefine existing methods in classes, even 
>>> after the classes have already been loaded. While you cannot add or 
>>> remove methods or fields, we might be able to re-work our PCEnhancer 
>>> to use a newly-generated inner class and a lookup in some 
>>> IdentityHashMap to perform the same function. E.g., instead of our 
>>> currently enhanced
>>> class:
>>>
>>> public class SomeEntity {
>>>   private String someField;
>>>   private StateManager stateManager; // generated
>>>
>>>   public String getSomeField() {
>>>     return pcgetSomeField(this);
>>>   }
>>>
>>>   // generated method
>>>   private static String getSomeField(SomeEntity entity) {
>>>     if (entity.stateManager == null)
>>>       return entity.someField;
>>>     else
>>>       entity.stateManager.getField(1, entity);
>>>   }
>>> }
>>>
>>>
>>> we would instead do something like:
>>>
>>>
>>> public class SomeEntity {
>>>   private String someField;
>>>
>>>   public String getSomeField() {
>>>     return GeneratedInnerClass.pcgetSomeField(this);
>>>   }
>>>
>>>   private static class GeneratedInnerClass {
>>>
>>>     private static String getSomeField(SomeEntity entity) {
>>>       StateManager stateManager = GlobalIdentityMap.get(entity);
>>>
>>>       if (stateManager == null)
>>>         return entity.someField;
>>>       else
>>>         stateManager.getField(1, entity);
>>>     }
>>>   }
>>> }
>>>
>>>
>>>  From the brief amount of time I've spent thinking about this, I 
>>> think we can get 99% of the way there with our current approach.
>>>
>>> The remaining 1% is a situation where if someone creates an instance 
>>> of SomeEntity *before* we ever initialize the BrokerFactory (and 
>>> thus perform the re-definition of known entity classes), we might 
>>> get passed an entity instance that isn't persist-able (since you 
>>> cannot redfine the methods for an already-created object, only for 
>>> objects that will subsequently be created).
>>>
>>>
>>> In summary, we have 3 different possibilities for removing the 
>>> requirement for build-time enhancement and launch-time agent
>>> specification:
>>>
>>> 1. Use reflection: considerably slower, would require drastic rework 
>>> of all our interaction with PersistenceCapable instances, but 
>>> wouldn't require any fancy class-generation/enhancement
>>>
>>> 2. Dynamic subclassing: easier to implement, but would require 
>>> people to use property accessors for everything, and wouldn't 
>>> support
>>> EntityManager.persist(someInstance)
>>>
>>> 3. Dynamic agent attachment and class re-definition: more difficult 
>>> to implement than #2, and would require JDK 1.6 + JVM 
>>> implementation-dependent attachment mechanisms, but might provide 
>>> the most functionality
>>>
>>>
>>> Does anyone have any thoughts about this? Especially any new ideas 
>>> for other ways to do this would be very interesting for all of us to hear.
>>>
>>>
>>> On May 17, 2007, at 8:19 AM, Patrick Linskey wrote:
>>>
>>>>> How hard is it to add a reflection/cglib type alternative to the 
>>>>> upfront bytecode generation (like hibernate does) to save us from 
>>>>> the development-time pain?
>>>>
>>>> Not particularly hard. There are a few APIs that would break for 
>>>> some cases,  but it's even pretty straightforward to do a 
>>>> subclassing approach for property-based access type without losing 
>>>> much performance -- the only cost in that configuration is with 
>>>> persistent-new instances.
>>>>
>>>> -Patrick
>>>>
>>>> On 5/17/07, James.Strachan <james.strachan@gmail.com> wrote:
>>>>>
>>>>> Firstly before I start, openjpa is a great piece of software; I'm 
>>>>> particularly fond of the documentation and in particular the query 
>>>>> language parts. The CSS for the site is also awesome :)
>>>>>
>>>>> However compared to hibernate, openjpa is still pretty painful to 
>>>>> use from an end users perspective and I don't think this should be 
>>>>> the case; plus I don't think it'll take much time to fix. While 
>>>>> the pain is still fresh in my mind I thought I'd post on how much 
>>>>> more painful openjpa is to use in a project. If you're short on 
>>>>> time, the basic idea is its that bytecode post processing stuff 
>>>>> thats to blame :). Yes I know its probably faster that way
>>>>> - its just so painful for Java programmers to work with. (And yes 
>>>>> I know one day we'll all have IDE plugins that hide the bytecode 
>>>>> stuff etc etc).
>>>>>
>>>>> So the first thing is having to mess with your build (ant or 
>>>>> maven) to get the post processing properly integrated. Depending 
>>>>> on if you have persistent entities in your main or test area this 
>>>>> can often trip you up a little (as it did me). I don't know about 
>>>>> folks on this list but the whole idea of having to mess with my 
>>>>> maven build gives me the jitters :). When you get that far & the

>>>>> maven planets are aligned with openjpa, the next hurdle you hit is 
>>>>> how do you run stuff in your IDE. If like me you use IDEA and 
>>>>> maven 2, the project gets auto-created by default for all projects 
>>>>> you work on.
>>>>> However these don't work when you use openjpa as you hit the 
>>>>> dreaded 'cannot function at all as you've not run the up front 
>>>>> bytecode post processor you dummy!' type error when trying to run 
>>>>> stuff in your IDE.
>>>>>
>>>>> So you then add the maven-generated classes to the front of the 
>>>>> classpath in your project. Hooray, after a day or two's work, you 
>>>>> can now actually use openjpa in your IDE and your build. YAY! The 
>>>>> downside is that now when navigating around your Java code, 
>>>>> whenever you navigate into an entity bean, IDEA shows you the 
>>>>> bytecode - not the source code as its confused since the bytecode 
>>>>> generated stuff is different to the source code it knows about. So 
>>>>> now you're faced with a dilemma - choose between navigating nicely 
>>>>> around your source code - or being able to actually run/debug your 
>>>>> application. I won't even get into the refactoring pain or having 
>>>>> to continuously run maven builds while developing code to avoid 
>>>>> getting code completion/compile errors etc. (I prefer to keep in 
>>>>> my IDE where possible).
>>>>>
>>>>> Compare this whole malarkey with hibernate. You add hibernate to 
>>>>> your pom, generate your project and you're good to go. No messing 
>>>>> with your project build; no messing with some secret ninja IDE 
>>>>> stuff to be able to actually run & debug your code while still 
>>>>> being able to actually navigate the source. It just works. Now it 
>>>>> might work in a crappy & slow way and openjpa might be way way 
>>>>> more efficient and powerful and whatnot - but I'd rather have a 
>>>>> cheap car that just works than a ferrari that you can only drive 
>>>>> on a tuesday if its sunny, but not too hot and refuses to even 
>>>>> start if its wet.
>>>>>
>>>>> FWIW I've just given up using openjpa for development; its just 
>>>>> way too painful. (I'm even hacking projects I work on so I use 
>>>>> openjpa in the maven build but explicitly switch to hibernate in 
>>>>> development mode; yeah its more work but at least I can use my IDE 
>>>>> properly again).
>>>>>
>>>>> I'm cool with putting post processing into the build system 
>>>>> (though that should really only be an optimisation); but please 
>>>>> can we have some inefficient but usable reflection/cglib type 
>>>>> approach so folks can easily switch from hibernate to openjpa (and 
>>>>> stay there) without pulling out our hair & swearing too much - or

>>>>> sneaking back at the first opportunity to get an easy life?
>>>>>
>>>>> Please don't take this mail the wrong way - I truly want openjpa 
>>>>> to be a success, its a great piece of software. Its just a bit too 
>>>>> hard to use out of the box right now. I'd truly like it to be 
>>>>> trivial to switch from hibernate to openjpa and never have to go 
>>>>> back.
>>>>>
>>>>> How hard is it to add a reflection/cglib type alternative to the 
>>>>> upfront bytecode generation (like hibernate does) to save us from 
>>>>> the development-time pain?
>>>>>
>>>>> --James
>>>>> -------
>>>>> http://macstrac.blogspot.com/
>>>>>
>>>>> --View this message in context:
>>>>> http://www.nabble.com/the-pain-of-post-processing-bytecode-%28anot
>>>>> her-beg-for-a-simple-reflection-cglib-alternative-like-hibernate%2
>>>>> 9-tf3770760.html#a10660986
>>>>>
>>>>>
>>>>> Sent from the open-jpa-dev mailing list archive at Nabble.com.
>>>>>
>>>>>
>>>>
>>>>
>>>> --Patrick Linskey
>>>> 202 669 5907
>>>
>>>
>>
>>
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> 
> 


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