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From "Barnett, Brian W." <brian.barn...@pearson.com>
Subject RE: Transaction question
Date Thu, 18 Aug 2005 15:50:50 GMT
Niels,
Thanks for the info. Maybe I am not totally understanding how your modified
code works, but is it meant to handle nested transactions?

If a transaction has already been started, then your modified code will
simply call invoke. I understand that. What happens when a nested
transaction calls commitTransaction()? (Like doSomethingElse() calling
doSomething() in the sample code below.) commitTransaction() gets called
twice in this example. I believe it will throw an exception.

What I was considering was to add a ThreadLocal transactionCounter variable
to DaoContext. start, commit and end transaction methods might look
something like this:

  public void startTransaction() {
    transactionCounter++;          // <-- NEW LINE OF CODE
    if (transactionCounter == 1) { // <-- NEW LINE OF CODE
      if (state.get() != DaoTransactionState.ACTIVE) {
        DaoTransaction trans = transactionManager.startTransaction();
        transaction.set(trans);
        state.set(DaoTransactionState.ACTIVE);
        daoManager.addContextInTransaction(this);
      }
    }                              // <-- NEW LINE OF CODE
  }

  public void commitTransaction() {
    if (transactionCounter == 1) { // <-- NEW LINE OF CODE
      DaoTransaction trans = (DaoTransaction) transaction.get();
      if (state.get() == DaoTransactionState.ACTIVE) {
        transactionManager.commitTransaction(trans);
        state.set(DaoTransactionState.COMMITTED);
      } else {
        state.set(DaoTransactionState.INACTIVE);
      }
    }                              // <-- NEW LINE OF CODE
  }

  public void endTransaction() {
    try {                            // <-- NEW LINE OF CODE
      if (transactionCounter == 1) { // <-- NEW LINE OF CODE
        DaoTransaction trans = (DaoTransaction) transaction.get();
        if (state.get() == DaoTransactionState.ACTIVE) {
          try {
            transactionManager.rollbackTransaction(trans);
          } finally {
            state.set(DaoTransactionState.ROLLEDBACK);
            transaction.set(null);
          }
        } else if (transactionCounter == 1) {
          state.set(DaoTransactionState.INACTIVE);
          transaction.set(null);
        }
      }                     // <-- NEW LINE OF CODE
    } finally {             // <-- NEW LINE OF CODE
      transactionCounter--; // <-- NEW LINE OF CODE
    }                       // <-- NEW LINE OF CODE
  }

The idea being that the transaction related logic only executes when we are
dealing with the first transaction bracket that was opened. I haven't
actually tried this out, but I think I will. Let me know if you, or anyone
else, sees any problems with this approach.

Thanks,
Brian Barnett

-----Original Message-----
From: Niels Beekman [mailto:n.beekman@wis.nl] 
Sent: Wednesday, August 17, 2005 3:00 PM
To: user-java@ibatis.apache.org
Subject: RE: Transaction question


Hi,

I'm facing this exact same problem however in a somewhat different context,
see the following archived thread:

http://www.mail-archive.com/ibatis-user-java@incubator.apache.org/msg025
80.html

http://www.mail-archive.com/user-java@ibatis.apache.org/msg00036.html

I recently restarted my investigation into this problem and have tried some
hacks in the iBATIS code, the changes were made in DaoProxy.java (which
proxies DAO-interfaces to provide transaction-semantics) and DaoContext.java
(which handles the transactions itself). Of course this is rather messy, but
I really do not like the SavePoint-support mentioned in the thread above, I
think it is rather a workaround than a solution.

Anyway, my changes (totally unverified, without any guarantees) in package
com.ibatis.dao.engine.impl:

DaoContext.java, added isTransactionRunning():

public boolean isTransactionRunning() {
  return transaction.get() != null;
}

DaoProxy.java, modified invoke(): see attached file.

This seems to work pretty good in my case, however further investigation is
required.

I hope the iBATIS devteam can comment on my solution, whether you think it
will work, or when you believe it really sucks :)

Greetings,

Niels

-----Original Message-----
From: Barnett, Brian W. [mailto:brian.barnett@pearson.com] 
Sent: woensdag 17 augustus 2005 22:00
To: 'user-java@ibatis.apache.org'
Subject: Transaction question

What are some good options to deal with the following:

ServiceClass1
public void doSomething() {
	try {
		daoManager.startTransaction();
		// Write some stuff to a database
		daoManager.commitTransaction();
	} catch (Exception e) {
		throw e;
	} finally {
		daoManager.endTransaction();
	}
}

ServiceClass2
public void doSomethingElse() {
	try {
		daoManager.startTransaction();
		ServiceClass1 sc1 = new ServiceClass1();
		sc1.doSomething();
		// Write some stuff to a database
		daoManager.commitTransaction();
	} catch (Exception e) {
		throw e;
	} finally {
		daoManager.endTransaction();
	}
}

The doSomethingElse() method will fail because startTransaction() gets
called twice. I need a good way to be able to re-use business logic methods
in different, or the same, service layer classes.

One thing I have done in the past is create a whole new layer, essentially a
service delegate, where I have moved all the transaction logic to. I didn't
like that too much because it was just a huge proliferation of methods just
to solve the "no nested transaction" problem.

I have also passed flags into methods to indicate if a transaction has
already been started, but passing flags is messy to say the least.

Any great ideas out there?

TIA,
Brian Barnett

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