Just for clarification: Where do the execution of a command goes, when the
execution is not simply a state update (like in most examples found online)
For instance, in my case,
-
The *Command* is *FetchLastHistoryChangeSet* which consist in fetching
the last history changeset from an external service based on where we left
off last time. In other words the time of the newest change of the previous
history ChangeSet Fetched.
-
The *Event* would be *HistoryChangeSetFetched(changeSet, time)*. In
correlation to what has been said above, the time should be that of the
newest change of the newly history ChangeSet Fetched (as per the command
event currently being handled)
Now in all example that i see, it is always: (i) *validating the command*,
then, (ii) *persisting the event*, and finally (iii) *handling the event*.
It is in *handling the event* that i have seen custom code added in
addition to the updatestate logic. Where, the custom code is usually added
after the update state function. But this custom is most of the time about
sending message back to the sender, or broadcasting it to the event bus.
As per my example, it is clear that i need to do quite few operation to
actually call*Persist(HistoryChangeSetFetched(changeSet, time))*. Indeed i
need the new changeset, and the time of the newest change of it.
The only way i see it possible is to do the fetch in the *validating the
command*
That is:
case FetchLastHistoryChangeSet => val changetuple =
ValidateCommand(FetchLastHistoryChangeSet);
persit(HistoryChangeSetFetched(changetuple._1, changetuple._2)) {
historyChangeSetFetched =>
updateState(historyChangeSetFetched)}
Where the ValidateCommand(FetchLastHistoryChangeSet)
would have as logic, to read last changeSet time (newest change of the
changeSet), fetch a new changeset based on it, if it exist, get the time of
its newest change, and return the tuple.
My question is, is that how it is supposed to work. Validating command can
be something as complex as that ? i.e. actually executing the command ?
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