szoio
commented
5 years ago Currently we have an invalid sequence handler strategy, that currently is driven off the enum value InvalidSequenceStrategy, which can either be LastWriteWins or Strict.
LastWriteWins disables sequence checking completely, whereas Strict enables it for everything.
Ideally we want something in between. For example, we should be able to credit an account (i.e. increase balance) as many times as we like without caring about the current sequence. If shouldn't either necessarily disrupt an account debit command that contains the sequence number of the previous debit, even if it make a debit account command sequence out of date.
For this strategy we really want to be able to label some commands as safe, and some as unsafe.
(LastWriteWins above means all are safe, Strict means all are unsafe).
Then a command should be considered valid if either.
- It is a sage command, regardless of the sequence number.
- Is is an unsafe command, and the sequence number is greater than or equal to the sequence number of the most recent unsafe write.
To implement this probably requires storing two sequence numbers with the aggregate - the latest sequence number, and in addition the latest unsafe sequence number.
It would be great if we could add some API/Helper methods for conflict resolution when there is an optimistic concurrency error. This really should be a potential addition to the CommandHandler for any specific command.