projection-patterns

1# Projection Patterns
2 
3Comprehensive guide to building projections and read models for event-sourced systems.
4 
5## When to Use This Skill
6 
7- Building CQRS read models
8- Creating materialized views from events
9- Optimizing query performance
10- Implementing real-time dashboards
11- Building search indexes from events
12- Aggregating data across streams
13 
14## Core Concepts
15 
16### 1. Projection Architecture
17 
18```
19┌─────────────┐     ┌─────────────┐     ┌─────────────┐
20│ Event Store │────►│ Projector   │────►│ Read Model  │
21│             │     │             │     │ (Database)  │
22│ ┌─────────┐ │     │ ┌─────────┐ │     │ ┌─────────┐ │
23│ │ Events  │ │     │ │ Handler │ │     │ │ Tables  │ │
24│ └─────────┘ │     │ │ Logic   │ │     │ │ Views   │ │
25│             │     │ └─────────┘ │     │ │ Cache   │ │
26└─────────────┘     └─────────────┘     └─────────────┘
27```
28 
29### 2. Projection Types
30 
31| Type           | Description                 | Use Case               |
32| -------------- | --------------------------- | ---------------------- |
33| **Live**       | Real-time from subscription | Current state queries  |
34| **Catchup**    | Process historical events   | Rebuilding read models |
35| **Persistent** | Stores checkpoint           | Resume after restart   |
36| **Inline**     | Same transaction as write   | Strong consistency     |
37 
38## Templates and detailed worked examples
39…