Install
Quick install
npx skills add https://github.com/wshobson/agents/tree/main/plugins/backend-development/skills/projection-patternsnpx skills add wshobson/agents --skill projection-patterns --agent claude-codenpx skills add wshobson/agents --skill projection-patterns --agent cursornpx skills add wshobson/agents --skill projection-patterns --agent codexnpx skills add wshobson/agents --skill projection-patterns --agent opencodenpx skills add wshobson/agents --skill projection-patterns --agent github-copilotnpx skills add wshobson/agents --skill projection-patterns --agent windsurfMore install options
Shorthand — useful for multi-skill repos:
npx skills add wshobson/agents --skill projection-patternsManual — clone the repo and drop the folder into your agent's skills directory:
git clone https://github.com/wshobson/agents.gitcp -r agents/plugins/backend-development/skills/projection-patterns ~/.claude/skills/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 │ │
└─────────────┘ └─────────────┘ └─────────────┘2. Projection Types
| Type | Description | Use Case |
| -------------- | --------------------------- | ---------------------- |
| Live | Real-time from subscription | Current state queries |
| Catchup | Process historical events | Rebuilding read models |
| Persistent | Stores checkpoint | Resume after restart |
| Inline | Same transaction as write | Strong consistency |
Templates and detailed worked examples
Full template library and detailed worked examples live in references/details.md. Read that file when you need the concrete templates.
Best Practices
Do's
- Make projections idempotent - Safe to replay
- Use transactions - For multi-table updates
- Store checkpoints - Resume after failures
- Monitor lag - Alert on projection delays
- Plan for rebuilds - Design for reconstruction
Don'ts
- Don't couple projections - Each is independent
- Don't skip error handling - Log and alert on failures
- Don't ignore ordering - Events must be processed in order
- Don't over-normalize - Denormalize for query patterns
SKILL.md source
--- name: projection-patterns description: Build read models and projections from event streams. Use when implementing CQRS read sides, building materialized views, or optimizing query performance in event-sourced systems. --- # 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 │ │ └─────────────┘ └─────────────┘ └─────────────┘ ``` ### 2. Projection Types | Type | Description | Use Case | | -------------- | --------------------------- | ---------------------- | | **Live** | Real-time from subscription | Current state queries | | **Catchup** | Process historical events | Rebuilding read models | | **Persistent** | Stores checkpoint | Resume after restart | | **Inline** | Same transaction as write | Strong consistency | ## Templates and detailed worked examples Full template library and detailed worked examples live in `references/details.md`. Read that file when you need the concrete templates. ## Best Practices ### Do's - **Make projections idempotent** - Safe to replay - **Use transactions** - For multi-table updates - **Store checkpoints** - Resume after failures - **Monitor lag** - Alert on projection delays - **Plan for rebuilds** - Design for reconstruction ### Don'ts - **Don't couple projections** - Each is independent - **Don't skip error handling** - Log and alert on failures - **Don't ignore ordering** - Events must be processed in order - **Don't over-normalize** - Denormalize for query patterns
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