Tutorials Design Patterns in C#
Event Sourcing Pattern — Audit & Replay Systems
Event Sourcing Pattern — Audit & Replay Systems: free step-by-step lesson with examples, common mistakes, and interview tips — part of Design Patterns in C# on Toolliyo Academy.
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Design Patterns in C# · Lesson 42 of 69
Event Sourcing Pattern — Audit & Replay Systems
GoF Core ✓ → Enterprise ✓ → Cloud & Craft
Cloud & Craft · 3 — Microservices & interviews · ~6 min · Module 5: Modern Enterprise Patterns
What is this?
Audit/replay focuses on rebuilding projections, time-travel debugging, and compliance exports from the event log.
Why should you care?
ShopNest finance asks “what was wallet balance at 5pm yesterday?” — replay answers.
See it live — copy this example
Paste into a C# console or class library project and run dotnet run.
Console.WriteLine("REPLAY events WHERE WalletId=@id AND At <= @t");
Console.WriteLine("FOLD -> balance snapshot");
Console.WriteLine("EXPORT event CSV for audit");What happened?
- Same event store as the basic lesson; emphasis on tooling: replay jobs, as-of queries, and export.
- Snapshots speed large streams.
Practice next
- Write a replay console for one wallet.
- Add as-of timestamp filter.
- Export events for an audit date range.
- Compare live balance vs replayed balance.
- Redact PII fields on export.
Remember
Replay rebuilds truth. As-of queries for audits. Snapshots for speed.
ShopNest wallet audit replay
Finance replays to 17:00 cutoff.
Outcome: Dispute evidence matches the ledger fold.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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