I am defining a state machine and would like to have the machine to "run" when the object is created. With that in mind I left out the triggers on all the transitions (and only defined guards). It seems though that a created object stays in the first state if not triggered further? How can I avoid having to call the trigger explicitly? If I do execute a trigger, all subsequent states are passed by that (one) trigger call? Is there something "special" with the first state?
The first state is special in not needing a trigger. The transition from start-state is executed on object creation.
To mimic the behavior you are looking for you can use the same trigger method on all other transitions. These transitions are guarded so that only 1 transition is valid at a time. But you will need to actually execute this single trigger to make anything happen.
You can now check if triggering is possible and if so trigger by this pseudo code:
if self.trigger? then self.trigger
Related
I have two actors that are overlapping at begin play. I can get the Overlapping Component(s) easy enough but, is there a way to manually call an OnComponentBeginOverlap event since it doesn't get called at BeginPlay if they are already Overlapping?
No, just create a separate event that follows the same execution as your OnComponentBeginOverlap event.
so my model works fine, but since I introduced conditional events (= an event that triggers once a specified condition is met), I find that the computational performance is decreased.
This is especially annoying when I run experiments with many iterations...
Is there an alternative way to trigger an event at a specified condition?
Thank you :)
The answer to this will be triggering events directly by the mechanism that are influencing the conditions you are monitoring. So instead of having the "permanent" condition check, make sure that each time the condition changes you are triggering a check. If that is not possible, because there are too many influencing factors, or it is continuosly changing, consider a cyclic check in discrete timesteps at an interval that suits you. Even this will be much more performant (depending on your choosen time check interval) then the current continous monitoring.
Example on how to do an event trigger monitoring instead of continous monitoring:
In your main, add global counter variable of type int (here: nrAgentsState1) and create a function to update that variable (here: updateStateCounter). Also in the function: a check that triggers a function whenever your threeshold is reached.
In your transition leading into the state you want to monitor (here: state1), call the function in main that updates the global counter. For the transition leading out of the monitored state, add the same action, but with a -1 as parameter.
I'm working on a PostgreSQL 9.3-database on an Ubuntu 14 server.
I try to write a trigger-function (AFTER EACH ROW) that launches an external process that needs to access the row that fired that trigger.
My problem:
Even tough I can run queries on the table including the new row inside the trigger, the external process does not see it (while the trigger function is still running).
Is there a way to manage that?
I thought about starting some kind of asynchronous function call to give the trigger some time to terminate first, but that's of course really ugly.
Also I read about notifiers and listeners, but that would require some refactoring of my existing code and also some additional listener, which I tried to prevent with my trigger. (I'm also afraid of new problems which may occur on this road.)
Any more thoughts?
Robin
Please correct me if I am wrong.
What I know about triggers is that they are triggered by events (Insert, Update, Delete). So we can run a stored procedure etc.. in the trigger.
This will give the application a good responsiveness because the query that the user interacts with, is quite small and this "other" longer time taking stuffs are taken care by the server internally as a separate task.
But I do not know about how the the triggers are handled inside the server. What I exactly want to know is what would happen in scenarios as given below.
Take Insert after trigger. And take trigger is executing a longer stored procedure. Then in the middle of the trigger there can be another insert. What I want to know is what will happen to that second trigger. If possible can I make that second trigger ignore itself.
marc_s has given the correct answer. I will copy it for the sake of completeness.
TRIGGERS ARE SYNCHRONOUS
If you want to have a asynchronous functionality go for a SQL broker implimenation.
Triggers are triggered by events - and then they are executed - right now. Since you cannot control when and how often they are triggered, you should keep the processing in those triggers to an absolute minimum - I always try to make - at most - an entry into another table (an "Audit" table) or possibly put a "marker" row into a "command" table. But the actual processing of that info - running stored procedures etc. - should be left to an outside job - don't do extensive processing in a trigger! This will reliably KILL all your performance\responsiveness.
I have a command that updates two aggregates. Since aggregate routes are transactional boundaries, I have a command that does a repository.Save() action on the first aggregate and then I fire another command (from within the first command) which acts on the second aggregate. Each Save() actions starts its Event-Store transaction and commits the changes and then publishes them.
First is this correct, i.e. letting one command notify another aggregate via another command?
I noticed in Mark Nihjof's code that he uses event handlers which is nice as you could register the event handlers to the same event. I tried doing this using J Oliver's Event-Store but my commits.events in IDispatchCommit were referencing the first aggregates values when processing the second. This caused some weird errors.
So should I find a way of making this work with EventHandlers or is firing off commands within commands okay?
JD
Edit - I have used switched my wire up to use .UsingAsynchronousDispatchScheduler() and am now allowing registered events to fire more than one event handler which in turn fires a command on the other aggregate and it seems to work. So, is this the correct way to do it and not use commmands firing commands?
I think there's a million and one ways to skin this cat. I'm not sure firing a command from an event handler is the way to go, I have to command handlers respond to the same command in this instance.
I do find documently good for a reference app. Have you looked a that?