Projection Patterns

If you're building event-sourced systems with CQRS, you'll eventually need to create read models from your event streams, and that's where this becomes essential. It provides concrete projector implementations that handle the mechanics of consuming events, maintaining checkpoints, and updating read models in databases or search indexes. The templates cover real scenarios like building order summaries from multiple event types and syncing data to Elasticsearch. What I appreciate is the focus on practical concerns like batch processing, error handling, and projection rebuilding. It's the kind of code you'd write anyway, but having tested patterns saves you from reinventing the checkpoint management and event handling infrastructure.

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last updated: Aug 21, 2026

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Install

$ npx -y skills add wshobson/agents --skill projection-patterns --agent claude-code

Installs into .claude/skills of the current project.

Files

Projection Patterns

Comprehensive guide to building projections and read models for event-sourced systems.

When to Use This Skill

Building CQRS read models
Creating materialized views from events
Optimizing query performance
Implementing real-time dashboards
Building search indexes from events
Aggregating data across streams

Core Concepts

1. Projection Architecture

┌─────────────┐     ┌─────────────┐     ┌─────────────┐
│ Event Store │────►│ Projector   │────►│ Read Model  │
│             │     │             │     │ (Database)  │
│ ┌─────────┐ │     │ ┌─────────┐ │     │ ┌─────────┐ │
│ │ Events  │ │     │ │ Handler │ │     │ │ Tables  │ │
│ └─────────┘ │     │ │ Logic   │ │     │ │ Views   │ │
│             │     │ └─────────┘ │     │ │ Cache   │ │
└─────────────┘     └─────────────┘     └─────────────┘