ddd-aggregate-design
Design rich domain aggregates with proper encapsulation, domain events, and the Export pattern. Use when implementing DDD aggregates with event sourcing patterns.
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Rich Domain Aggregate Design
Design and implement rich domain aggregates with proper encapsulation, domain events, and the Export pattern.
When to Use This Skill
- Designing new domain aggregates from scratch
- Refactoring anemic models to rich domain models
- Adding domain events to existing aggregates
- Reviewing aggregate design for encapsulation
Core Rules
Read DDD-RULES.md for all aggregate design rules. Key principles:
- Hide all fields - All struct fields must be private
- Actionable methods only - Expose domain operations, not getters
- Domain Events - Track state changes through events
- Export pattern - Use
Export()to expose state externally - Factory functions - Create aggregates only through validated factories
Quick Reference (Go Examples)
Factory Function Pattern
func NewOrder(customerID CustomerID, items []OrderItem) (*Order, error) {
if len(items) == 0 {
return nil, ErrEmptyOrder
}
o := &Order{
id: NewOrderID(),
status: OrderStatusPending,
events: &eventRegister{},
}
o.addEvent(applayer.NewEvent(OrderCreated{OrderID: o.id}))
return o, nil
}Actionable Method Pattern
func (o *Order) Ship(warehouse WarehouseID) error {
if o.status == OrderStatusCancelled {
return ErrOrderAlreadyCancelled
}
if o.status == OrderStatusShipped {
return nil // Idempotent
}
oldStatus := o.status
o.status = OrderStatusShipped
o.addEvent(applayer.NewEvent(OrderShipped{OldStatus: oldStatus}))
return nil
}Export Pattern
func (o *Order) Export() ExportedOrder {
return ExportedOrder{
ID: o.id.String(),
Status: string(o.status),
}
}
func (o *Order) ID() OrderID { return o.id } // Only identity getter allowed- Repository
- forgoty/dotfiles
- Commit
0d0cc99
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