commandhandling-optimistic-concurrency.puml

title Command Handling, Optimistic Concurrency

actor User
boundary Handler
boundary Repository
entity BarInstance
database EventStore
autonumber
User -> Handler : Set Foo = 2 where\nOriginalFoo = 1 on Bar
Handler -> Repository : Get Bar
Repository -> BarInstance : Create Bar instance
activate BarInstance
Repository -> EventStore : Get all Bar\nevents from Bar stream
Repository -> BarInstance : Apply all Bar events\nto Bar instance
Repository -> Handler : Return Bar, version = X

group Optimistic Check
  Handler -> BarInstance : Invoke method Foo
  BarInstance -> BarInstance : If OriginalFoo != 1\nthrow Concurrency Exception
  BarInstance -> Repository : Concurrency Exception
  Repository -> Handler : Concurrency Exception
  Handler -> User : Concurrency Exception
end

note right
        0 or more events raised by Bar
end note
Handler -> Repository : Save Bar
Repository -> BarInstance : Get events to append
deactivate BarInstance

group No events to append
  Repository -> Repository : If events.Count = 0, return
  Repository -> Handler: Return
  Handler -> User: Return
end
Repository -> EventStore : Append events to Bar stream
group Concurrency Exception
  EventStore -> EventStore : If stream version != X\nthrow Concurrency Exception
  EventStore -> Repository : Concurrency Exception
  Repository -> Handler : Concurrency Exception
  Handler -> User : Concurrency Exception
end
  EventStore -> EventStore : Stream appended
  EventStore -> Repository : Return
  Repository -> Handler : Return
  Handler -> User : Return