This repo contains a low-dependency set of infrastructure, examples and tests illustrating a consistent approach to Event-sourced Decision processing against ordered stream stores in F#.

The key consumer of this codebase is the Jet.com production site.

However, the codebase as a whole (particularly the Samples) are intended to achieve a critical secondary goal of sharing/discussing/prototyping usage patterns. As such, it's hoped to also have it be viable for use in the following contexts:

• a testbed for illustrating and prototyping decision/state processing mechanisms
• sample codebase for both internal- and external-facing Jet.com training events and talks
• base infrastructure for third party talks / tutorials

Please raise GitHub issues for any questions so others can benefit from the discussion.

• Foldunk.Handler: a store-agnostic Decision flow runner that fulfills key request processing objectives as dictated by the requirements of Jet.com's front-end API layer
• Foldunk.EventStore: Production-strength EventStore Adapter instrumented to the degree necessitated by Jet's production monitoring requirements
• sufficient logging and metrics instrumentation capabilties to be used in a Production context

• Does not emit any specific logs, but is sufficiently instrumented (using Serilog to allow one to adapt it to ones hosting context (we feed log info to Splunk atm and feed metrics embedded in the LogEvent Properties to Prometheus; see relevant tests for examples)
• Uses UnionEncoder: a scheme for the serializing Events modelled as an F# Discriminated Union with the following capabilities:
  • independent of any specific serializer
  • allows tagging of Discriminated Union cases with low-dependency DataMember(Name= tags in a versionable manner using TypeShape's UnionEncoder
• Compaction support: A pattern employed to optimize command processing by employing in-stream 'snapshot' events with the following properties:
  • no additional roundtrips to the store needed at either the Load or Sync points in the flow
  • support, when using the EventStore adapter (via UnionEncoder) for the maintenance of multiple co-existing snapshot schemas in a given stream (A snapshot isa Event)
• Integrated Folded state based caching via .NET MemoryCache - provides for minimal reads by maintaining the folded state in the cache without any explicit code within the Domain Model.

dotnet msbuild Foldunk.sln "-t:restore;build;pack;test"