Use your database to power state machines

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• lysdexic@programming.dev ⁨1⁩ ⁨year⁩ ago

  Is it just me or is this a nightmare approach to software maintenance? Each state transition requires a database trip, state machine transitions are determined at runtime and there’s no simple way to reproduce them locally, and in the case of the state machine database going down the system simply cannot work.

  What exactly is the selling point of this approach?

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  • Deebster@lemmyrs.org ⁨1⁩ ⁨year⁩ ago

    It's long running, so you want a database so you can store your state. If you're storing state, locking it into a state machine makes sense.

    I do agree with some of the commenters that making it closer to an event source design would make more sense still.

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    • lysdexic@programming.dev ⁨1⁩ ⁨year⁩ ago

      It’s long running, so you want a database so you can store your state. If you’re storing state, locking it into a state machine makes sense.

      That’s besides the point. Of course that the most fitting way to represent a state machine is with a state machine. The point is that implementing the transition table in a database table creates many problems while apparently solving none.

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• robyoung@beehaw.org ⁨1⁩ ⁨year⁩ ago

  I don’t understand why the most_recent field is needed. Surely the most recent state can be derived from the order field and the unique constraint on it can prevent concurrency issues if the previous sequence is taken before the state change. The benefit would be that the transition history table could then be append only.

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  • ck_@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago

    Yeah, I’m wondering that too. Also, why would a transition ever be updated? Should a successful transition not be a write-once operation? I guess it boils down to the finer details of the requirements of the application.

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    • towerful@programming.dev ⁨1⁩ ⁨year⁩ ago

      I think the most_recent is to power the unique index constraint. This “powers” the whole thing.

      Whereas the sort_order is to allow easy sorting, which is just for human readability. You could argue that you can rely on the “created_at” for this.
      Considering the examples increment it by 10, I assume this is to allow admins to manually override a sequence or force a data consistency thing or whatever.

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• glarf@lemmy.world ⁨1⁩ ⁨year⁩ ago

  Neat! Thanks for sharing

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• Jaysue@sh.itjust.works ⁨1⁩ ⁨year⁩ ago

  Thank you for sharing.

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