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POWindows service design
 

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    <p>Imagine the following situation. Windows service from time to time checks the data in database table. When some new data appears, it starts processing each new row.</p> <p>The processing consists of several logical stages, let it be: </p> <ul> <li>get some additional data from web service;</li> <li>find an existins object via web service by data from stage 1 or create a new object;</li> <li>inform an interested person of the actions done (with details about the object that was found/created on stage 2);</li> <li>do smth else.</li> </ul> <p>Just for now if any exception happens, the service updates the DB row and sets a flag indicating that a mistake has happened. Some time later service will try to process the row once again... and here is the problem.</p> <p>Processing will start from the very beginning, from stage 1. In this case if exception happened on stage 4 and if it will happen again and again the interested person from stage 3 will be informed again and again and again...</p> <p>To completely stop row processing in case of exception is not possible and not desirable in my situation. Ideally it would be nice if there was a way to start processing from the stage where it failed last time.</p> <p>Now I need your advice how all these can be handled. In fact, everything is even more complicated, because there are several patterns of processing, different number of stages and so on. </p> <p>Thanks in advance.</p> <p><strong>UPDATE</strong> </p> <p>Yes, I have the State parameter in data rows :) It is just not used just for now. And exception handling is not a new thing for me.</p> <p>The question is: what is the best way to handle state switching? In other words to make a clear logical link between stage number and processing method? The flow of execution can be very diffirent and include various number of stages and methods for different rows.</p> <p>I hope, there are more pleasant ways than writing endless switch/case blocks for every new sutiation?</p>
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    1. COFor reference: If your main reason for having a service is to run some stuff "from time to time", chances are what you need isn't a windows service, but a scheduled task.
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