Add no-op TransactionOperations implementation

[vpavic]

A no-op implementation can be useful for:

• having TransactionOperations consuming code switch to non-transactional behavior by injecting NoOpTransactionOperations instead of TransactionTemplate
• testing purposes

For first point we have a use case in Spring Session's JdbcOperationsSessionRepository. I've used similar approach in a number of other projects so having Framework provide it OOTB would be nice. Also note that TransactionOperations isn't parameterized, but TransactionOperations#execute is which makes it impossible to have no-op implementation as lambda expression.

[sbrannen]

Thanks for the PR, @vpavic.

We'll consider it.

Also note that TransactionOperations isn't parameterized, but TransactionOperations#execute is which makes it impossible to have no-op implementation as lambda expression.

Yes, that is a bit unfortunate.

[jhoeller]

Good idea in general! I've implemented this slightly differently as a static withoutTransaction() method on TransactionOperations, along the lines of the recently introduced withDefaults() method on TransactionDefinition.

[vpavic]

I don't see anything pushed to the master yet so I'm not sure if I understood the described changes correctly, but if non-transactional behavior is implemented using a new operation on TransactionOperations I'm afraid that won't allow changing transactional behavior by injecting a different TransactionOperations implementation which was the motivation for this PR.

Ideally, TransactionOperations consuming code shouldn't be aware of the fact that there's no transaction involved. This is similar like to, for instance, changing propagation behavior by injecting a differently configured TransactionTemplate.

[jhoeller]

I'm about to commit this along with a number of other changes now, so it'll be in master in a moment. Thanks for your patience :-)

As for the implementation, withoutTransaction() is a new static factory method on TransactionOperations, returning a TransactionOperations instance with a regular execute method which executes the callback without an actual transaction. This should allow for substitution underneath any TransactionOperations caller as intended.