A question about Transactions in adba

[Douglas Surber]

Session.transactionCompletion does not start a transaction. It returns a new instance of TransactionCompletion. Nothing more. It does not do a round trip.

A TransactionOutcome indicates the outcome of a transaction completion. It is an enum.

A TransactionCompletion is used to signal to a endTransaction Operation how to complete the current active transaction. It is basically a mutable flag. Operations themselves are immutable once submitted. A TransactionCompletion is a mutable flag that an endTransaction Operation is configured with. After the endTransaction Operation is submitted the mutable TransactionCompletion can be modified to cause a rollback instead of the default commit.

Each call to Session.transactionCompletion returns a new instance. Multiple calls are fine.

Example:

	try (Session session = ds.getSession()) {
		TransactionCompletion completion = session.transactionCompletion();
		session.rowCountOperation(updateSql)
			.set(param, value)
			.onError( t -> completion.setRollbackOnly() )
			.submit();
		session.endTransaction(completion);
	}

By default a TransactionCompletion signals to end the transaction with a commit. So if there is no error the endTransaction Operation will commit the active transaction. If the UPDATE throws an error the TransactionCompletion will be flipped to signal a rollback, then when the endTransaction Operation is executed it will end the active transaction with a rollback.

Douglas

> On Nov 24, 2018, at 11:27 AM, Alexander Kjäll <alexander.kjall at gmail.com> wrote:
> 
> Hi
> 
> I have some questions about the Session.transactionCompletion() method
> and TransactionOutcome class.
> 
> Based on the example in Examples.transaction and the javadoc it looks
> like an transaction should be started when transactionCompletion() is
> called, this returns an TransactionOutcome object that can later be
> used to complete the transaction.
> 
> Questions:
> 1) Why isn't the transactionCompletion() method an operation on the
> same format as the other methods, starting an transaction requires
> network communication for postgresql and there is need of an mechanism
> to handle errors.
> 2) Is it required that it's the same TransactionOutcome object that is
> returned by starting the transaction that is used to commit/rollback
> it?
> 3) What should happen if transactionCompletion() is called multiple
> times without an commit/rollback, should the same object be returned
> or is it allowed to return new ones?
> 
> best regards
> Alexander Kjäll