Class StartAtTailAttribute
- Namespace
- Cratis.Chronicle.Reactors
- Assembly
- Cratis.Chronicle.dll
Attribute used to mark a reactor class as one that should not observe history that predates its first registration. The reactor begins at the tail of the event sequence the first time Chronicle sees it, and observes only what is appended from then on.
[AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
public sealed class StartAtTailAttribute : Attribute- Inheritance
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StartAtTailAttribute
- Inherited Members
- Extension Methods
Remarks
A new reactor normally catches up from the very beginning of the event sequence, as ordinary observation, so a reactor whose handlers cause side effects - sending a notification, calling an external system, starting a job - would act on every historical event the moment it is deployed. OnceOnlyAttribute does not prevent that, because it only excludes replay. This attribute does.
It only affects the first registration. A reactor that Chronicle already holds a position for keeps it, so the attribute is safe to leave in place and does not skip events after a restart. Renaming the reactor or moving its namespace changes its default identifier, which makes it a new reactor, and it begins at the tail again - unless an explicit identifier is given on ReactorAttribute. An explicit replay still replays from the beginning, because the attribute only chooses where a reactor starts.
Both the Chronicle server and the client must be on a version that supports it. A server that does not know about it ignores the request and the reactor catches up from the beginning.
Constructors
StartAtTailAttribute()
public StartAtTailAttribute()