About z_db transactions

[Alvaro Pagliari]

Hello,

I would like to know what is the correct way to use z_db:transaction(F, Context)...

I was creating a function

F = fun(Ctx) ->

       try

           %Here I would use z_db:q to execute queries...

           do_something_with_db(Ctx),

           ok

       catch

           X -> {rollback, X}

       end

     end,

z_db:transaction(F, Ctx).

But I noticed that even returning {rollback, error} instead of ok doesn't rollback the transaction. Is there a different/correct way to use this function?

This is on zotonic 0.62.0.

Cheers,

--

Álvaro Pagliari

[Marc Worrell]

Hi Alvaro,

The transaction function performs a rollback if:

 - Fun returns {rollback, …}

 - Fun throws an exception

 - The final COMMIT errors

And of course if the whole process is killed during the transaction.

In your case, are you sure you are passing the correct Context?

Normally I use:

F = fun(Ctx) -> …. (do something with Ctx) end,

z_db:transaction(F, Context).

Note that I pass Context to the transaction function, and inside the F only Ctx is used.

Cheers,

Marc

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[Alvaro Pagliari]

Hello,

I was talking with a friend about Postgres and he told me that postgres doesn't like long-running transactions. So, probably, the database is closing the transaction and starting a new one by itself. 

It seems postgres added an option to enable long-running transactions from version 9.6, but I need to research more to be sure about it.

Thanks!

--

Álvaro Gianni Pagliari
alvaropag [at] gmail [dot] com

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