Re: Inline scripted transactions

17 jul 2010 kl. 04.22 skrev Justin T. Sampson:

> On Fri, Jul 16, 2010 at 1:00 AM, Karl Wettin <[email protected]>  
> wrote:
> I find this very neat and think it's safe since transactions are
> "useless" after taking a snapshot.
>
> I'm not sure what you mean by "useless".

That a journal is "depricated" after taking a snapshot.

> Something else I might be missing that makes this a bad idea?
>
> Well, I suppose journals will be larger because they contain code  
> snippets rather than just class names. I wouldn't worry about that  
> unless it actually becomes a problem.
>
> You also, of course, lose compile-time checking of the syntax and  
> typesafety of the code. Presumably you have unit tests that will  
> exercise the scripts, though.

It also turns out to be rather slow when executing the journal.  
Perhaps 10-15 times slower. But I'm OK with that. My system almost  
never crash *knock on wood* and I take snapshots realatively frequent.

Here is some example code:
>
>     EntityTransactionScriptWithQuery<Advertisement> script = new  
> EntityTransactionScriptWithQuery<Advertisement>(advertisement);
>     script.invoke("source = entity.getSource(" +  
> script.get(advertisementSource.getURI()) + ");");
>     script.invoke("source.setLastSeen(executionTime);");
>
>     Boolean sold = harvester.isSold(searchResult,  
> advertisementDocument);
>     if (sold != null) {
>       if (!sold && advertisementSource.getClosed() != null) {
>         // mark as still for sale
>         script.invoke("source.setClosed(null);");
>
>       } else if (sold && advertisementSource.getClosed() == null) {
>         // mark as sold
>         script.invoke("source.setClosed(executionTime);");
>
>       }
>     }
>
>     Hydda.getInstance().executeTransaction(script);

Notice the first invokation that use "script.get(...". This will  
serialize any class to bean shell script using reflection. In this  
case it's just a string but it could be a complete object graph. (In  
the case of prevayler transactions this should of course be an  
isolated graph.)

I do enjoy the inline transactions. Makes for fast coding and easy to  
read code compared to decoupled transaction classes.

I haven't pushed the scripted transaction classes to github yet, but I  
will. In case anyone want it now just let me know.

Here is the Bsh helper though:
http://github.com/karlwettin/kodapan-common/blob/master/src/main/java/se/kodapan/bsh/BshScriptBuilder.java


	karl

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