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title: Aggregates
---

Aggregates are a core concept in Domain-Driven Design (DDD) and event sourcing. Arc provides seamless integration with Chronicle's aggregate roots, offering automatic dependency injection and event tracking.

## What are Aggregates?

An aggregate is a cluster of domain objects that can be treated as a single unit. The aggregate root is the entry point to the aggregate and ensures the consistency of changes within the aggregate boundary.

## Key Features

- **Automatic Registration**: Aggregate roots are automatically discovered and registered in the dependency injection container
- **Event Source ID Resolution**: Automatic resolution of aggregate instances based on the event source ID from command context
- **Change Tracking**: Automatic tracking of changes and events generated by aggregate roots
- **Transient Lifecycle**: Each request gets a fresh instance tied to a specific event source ID

## Topics

- [Aggregate Roots](/arc/backend/chronicle/aggregates/aggregate-roots/) - How to use aggregate roots with dependency injection and event sourcing
- [Aggregate Root](/arc/backend/chronicle/aggregates/aggregate-root/) - Defining and implementing aggregate roots