transaction as subroutine appears to be unworkable in my case #24

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xenoterracide opened this Issue Oct 27, 2012 · 9 comments

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I'm trying to write a Unit of Work object http://martinfowler.com/eaaCatalog/unitOfWork.html with DBIx::Connector as the underlying connector, unfortunately as I look at it I'm unable to resolve any way that I can use Connectors transaction support using this pattern.

The reason for this is that my begin needs to start in a different method from commit, and the only way I have seen to resolve this is to move it to a higher level, but I don't like that because that puts database specific code at a layer higher than I want.

would you add something like DBIC's txn guard? expose support for DBI's native transaction support? or maybe add callbacks that are more like AnyEvent::DBI's (considering switching to that)

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theory commented Oct 29, 2012

I wouldn't turn down a patch that offered a lightweight implementation of such a thing. I don't think it would need to be very complicated. I'd like to see what it looked like, though.

well my thought would be just to use DBI's functionality, but glancing over your code you are using the underlying DBD's directly and I'm not sure why. Why is DBI's own transaction interface insufficient?

the more I'm looking over it, I'm thinking the simple solution of exposing DBI's methods would work.

$rc  = $dbh->begin_work;
$rc  = $dbh->commit;
$rc  = $dbh->rollback;
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theory commented Nov 2, 2012

FWIW, setting AutoCommit is the DBI's interface. The transaction methods you mention were added later.

But to answer your question, the direct hash stuff is used so that things can be locally scoped.

they may have been added later but they're still useful, the thing is I'll have to turn autocommit off and manually handle the transactions. I think begin_work may be optional, but it seems like a good idea to use.

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theory commented Nov 2, 2012

It is but sometimes it's not the right choice. If you were to switch DBIx::Connector over to them, I'm pretty sure the tests will fail. The ability to use local is crucial to allowing nested calls to txn and friends.

I'm getting the feeling that allowing an interface that allows me to have an interface similar to ->begin ->commit isn't going to work. I don't really care if it passes through or works in a completely different way... it's just the problem of having readers operate outside of writers but needing them to happen within a single (or nested) transaction to have actual ACID-ity. I'll look into seeing if it can be made to work this weekend (if tuits), since DBIC has it, and your code I belive copies theirs it should be possible.

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theory commented Nov 2, 2012

It can be done. DBIc implements txn_do() with its transaction guard stuff. The thing to do would be to add the guard interface to Connector without regard to txn(), at first. Then modify txn() to use the guard interface.

out of curiousity? because I've never really turned autocommit off... but it appears by DBI's doc if it's off you have to call commit. How does ::Connector handle autocommit off now?

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theory commented Nov 2, 2012

Like this -- yes, using begin_work, commit, and rollback. Looks like I forgot that DBIx::Connector does not set AutoCommit. It just checks it to see if it's in a transaction or not (begin_work turns it off, commit and rollback turn it on).

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