CQRS Implementation Skill

CQRS Implementation

Comprehensive guide to implementing CQRS (Command Query Responsibility Segregation) patterns.

When to Use This Skill

Separating read and write concerns
Scaling reads independently from writes
Building event-sourced systems
Optimizing complex query scenarios
Different read/write data models needed
High-performance reporting requirements

Core Concepts

1. CQRS Architecture

                    ┌─────────────┐
                    │   Client    │
                    └──────┬──────┘
                           │
              ┌────────────┴────────────┐
              │                         │
              ▼                         ▼
       ┌─────────────┐          ┌─────────────┐
       │  Commands   │          │   Queries   │
       │    API      │          │    API      │
       └──────┬──────┘          └──────┬──────┘
              │                         │
              ▼                         ▼
       ┌─────────────┐          ┌─────────────┐
       │  Command    │          │   Query     │
       │  Handlers   │          │  Handlers   │
       └──────┬──────┘          └──────┬──────┘
              │                         │
              ▼                         ▼
       ┌─────────────┐          ┌─────────────┐
       │   Write     │─────────►│    Read     │
       │   Model     │  Events  │   Model     │
       └─────────────┘          └─────────────┘

2. Key Components

| Component | Responsibility | | ------------------- | ------------------------------- | | Command | Intent to change state | | Command Handler | Validates and executes commands | | Event | Record of state change | | Query | Request for data | | Query Handler | Retrieves data from read model | | Projector | Updates read model from events |

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

Separate command and query models - Different needs
Use eventual consistency - Accept propagation delay
Validate in command handlers - Before state change
Denormalize read models - Optimize for queries
Version your events - For schema evolution

Don'ts

Don't query in commands - Use only for writes
Don't couple read/write schemas - Independent evolution
Don't over-engineer - Start simple
Don't ignore consistency SLAs - Define acceptable lag

Agent Skills: CQRS Implementation

Install this agent skill to your local

Skill Files