sqlx::Transaction and Arc<Mutex> (lemm.ee)

submitted 2 weeks ago by Cpo@lemm.ee to c/rust@programming.dev

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In order to share the running transaction into a DAO style data management class, I have wrapped the transaction in an Arc and pass it into the DAO.

The issue is, once the transaction is in there I cannot call commit() on it because it cannot be moved out of the Arc anymore, as the commit requires a mut self.

Any ideas on how to work around this?

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[-] nous@programming.dev 6 points 2 weeks ago

Transactions should be short lived, they block data on the database side from acessing those tables or rows. Best to not jole onto a transaction that long and instead gather your data first or rethink your access patterns to your data base.

But arc does give you a try_unwrap which returns the inner type if there is only one strong copy left. And mutex gives you an into_inner to move out of it. But really transactions should not be held for a long period of time.

[-] Cpo@lemm.ee 2 points 2 weeks ago

Seems like the into_inner is the way (i see other references to it).

And yes, transactions should be short-lived, this is just about delegating it to the responsible component.

[-] nous@programming.dev 2 points 2 weeks ago

Not sure why you need an arc mutex to delegate it to the responsible component. Seems like the type of thing that should not cross thread boundaries nor be cloned multiple times.

[-] Cpo@lemm.ee 1 points 2 weeks ago

Not talking threads here, more Tokio tasks.

[-] BB_C@programming.dev 5 points 2 weeks ago

You appear to be generally confused.

If you're using the multi-threaded work-stealing tokio runtime (the default), you are "talking threads". And if you aren't, Arc and Mutex would be useless, irregardless of whether you're doing it right or wrong.