Re: New to Prevayler: "Baptism problem" basics?

Hi, Naveen

The principle is: what is within Prevayler's protection should never be
accessed without this protection.

I'll try to explain the baptism issue through an example:

class ModificationWithBaptismProblem implements Transaction {

private User user;
private String newPwd;
ModificationWithBaptismProblem(User u, String np) { user = u; newPwd = np; }

void executeOn(prevalentSys) {
u.setPwd(newPwd);
}
}

class ModificationWithoutBaptismProblem implements Transaction {

private int userid;
private String newPwd;

ModificationWithoutBaptismProblem(int id, String np) { userid = id; newPwd =
np; }

void executeOn(prevaylerSys) {
((YourSys) prevaylerSys).getUser(userid).setPwd(newPwd);
}
}

the difference is that in the former the transaction will hold a reference
to an object that is out of Prevayler's protection ('cause it comes from the
application through the constructor).

Prevayler cannot assure that the referenced object will be the same when
executing the transaction recoverying process.

I'd say that your prevalent system (that comes as a param to executeOn()) is
the entry point for your business objects and you should access them only
through it (within transactions).

Hope it helps.
Dear friends, please, correct me if I'm wrong. Any additional comments would
be appreciated :D.

Best regards,
DB



On Fri, Sep 9, 2011 at 6:39 AM, Naveen Chawla <[email protected]> wrote:

> I really couldn't understand the term "remove the code that references
> business objects directly inside Transactions". I thought the very first
> line of the Transaction itself was
> ((MyObjectType)prevalentSystem).doSomething()? Isn't this referencing the
> business object directly to call the method in the first place? If I did
> MyObjectType m = (MyObjectType)prevalentSystem; , I could still use "m"
> thereafter, right? Am I ok as long as I call methods from "m" and not
> references? Or is it a different rule?
>
> Can my ".doSomething()" method itself reference and play around with the
> objects in "m" without restrictions?
>
> I'm lost maybe because the code examples on codehaus are gone:
> http://docs.codehaus.org/display/PREVAYLER/The+Baptism+Problem . And also
> because I couldn't understand the phrase "transactions shouldn't carry direct
>
> references to the objects". Does this only mean as instance variables of
> the Transaction, or also within local variables inside "executeOn()"?
>
> Can I get the simplest possible example with the problem vs without, and
> the best practices for easily and flexibly modifying objects top-to-bottom
> without ever having to worry about the baptism problem?
>
>
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------------------------------------------------------------------------------
Why Cloud-Based Security and Archiving Make Sense
Osterman Research conducted this study that outlines how and why cloud
computing security and archiving is rapidly being adopted across the IT 
space for its ease of implementation, lower cost, and increased 
reliability. Learn more. http://www.accelacomm.com/jaw/sfnl/114/51425301/

_______________________________________________
To unsubscribe go to the end of this page: http://lists.sourceforge.net/lists/listinfo/prevayler-discussion
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"Databases in Memoriam" -- http://www.prevayler.org