先看看示例
作者提供的示例，实际效果取决于你的输入和使用工具。
输入
为订单事件流设计一个支持实时看板的读模型投影，并说明如何保存检查点与重建。
输出
预期交付：投影架构设计、读模型表或视图方案、幂等与检查点策略及最佳实践清单。（编辑说明，非实际运行结果）
方法说明
--- 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