Decision Matrix

This matrix helps choose between Bus Mode (CQRS) and Direct Mode (Use Case) based on operation complexity.

Quick Decision Tree

Does the operation need domain events?
├─ YES → Bus Mode
└─ NO
    └─ Does it involve multiple entities or complex business rules?
        ├─ YES → Bus Mode
        └─ NO → Direct Mode

Comparison Table

Criterion	Direct Mode	Bus Mode
Simple CRUD	✅ Recommended	❌ Over-engineered
Complex business logic	⚠️ Possible	✅ Recommended
Domain events needed	❌ Manual	✅ Automatic
Multi-entity transactions	⚠️ Manual	✅ Built-in
Middleware support	❌ No	✅ Yes
Async processing	❌ Hard to add	✅ Easy to add
Development speed	✅ Faster	⚠️ More boilerplate

When to Use Direct Mode

Simple read operations (homepage, about page)
List/detail views without business logic
Public read-only API endpoints
Rapid prototyping

When to Use Bus Mode

Operations requiring domain events
Complex business rules
Multi-entity transactions
Operations needing middleware (logging, authorization)
Write operations with side effects

Examples from Demo Application

Direct Mode: Homepage module displays a simple welcome message.

Bus Mode: Library module handles book CRUD with events and permissions. Loan module manages complex borrowing/return workflows. User module handles authentication with security events.

Best Practices

Start Simple: Begin with Direct Mode for unclear requirements, migrate when complexity emerges
Module Consistency: Avoid mixing modes within a single module
Choose Based on Needs: If events, transactions, or middleware are known upfront, start with Bus Mode