How Do I...?

A task-oriented index into the Protean documentation. Find the guide you need by what you're trying to accomplish.

Model My Domain

I want to...	Guide
Define a root entity with business logic	Aggregates
Add a child object with identity to an aggregate	Entities
Create an immutable descriptive value (Money, Email, Address)	Value Objects
Choose between an entity and a value object	Deciding Between Elements
Connect entities with relationships	Relationships
Add typed attributes to domain objects	Fields
Define a domain event	Events

I want to...	Guide
Validate field values	Validations
Enforce business invariants	Invariants
Change aggregate state safely	Aggregate Mutation
Raise domain events from an aggregate	Raising Events
Coordinate logic across multiple aggregates	Domain Services

I want to...	Guide	Pathway
Handle a user request synchronously	Application Services	DDD
Define a command representing user intent	Commands	CQRS, ES
Process a command and update an aggregate	Command Handlers	CQRS, ES
Save an aggregate to the database	Persist Aggregates	All
Load an aggregate by ID or query	Retrieve Aggregates	All
Manage transactions	Unit of Work	All

I want to...	Guide
Run side effects when an event fires	Event Handlers
Build a read-optimized view from events	Projections
Listen to messages from an external broker	Subscribers

I want to...	Guide
Register domain elements	Register Elements
Initialize and activate a domain	Initialize Domain
Configure databases, brokers, and caches	Configuration
Understand identity and ID generation	Identity
Understand stream categories	Stream Categories

I want to...	Guide
Process events and commands asynchronously	Server
Understand subscriptions and event processing	Subscriptions
Use the outbox pattern for reliable messaging	Outbox
Use the CLI for development and operations	CLI

I want to...	Guide
Understand the three architectural pathways	Choose a Path
Use pure DDD with application services	DDD Pathway
Separate reads and writes with CQRS	CQRS Pathway
Use event sourcing for full audit trails	Event Sourcing Pathway
Decide between CQRS and Event Sourcing	Architecture Decision

I want to...	Guide
Test domain model logic	Domain Model Tests
Test application workflows (BDD-style)	Application Tests
Test with real databases and brokers	Integration Tests
Set up test fixtures and patterns	Fixtures and Patterns

I want to...	Guide
Use PostgreSQL	PostgreSQL Adapter
Use Elasticsearch	Elasticsearch Adapter
Use Redis as a message broker	Redis Broker
Use Redis as a cache	Redis Cache
Use Message DB as an event store	Message DB
Build a custom broker adapter	Custom Brokers