In the context of the repository pattern, aggregate roots are the only objects your client code loads from the repository.
The repository encapsulates access to child objects – from a caller’s perspective it automatically loads them, either at the same time the root is loaded or when they’re actually needed (as with lazy loading).
For example, you might have an Order
object which encapsulates operations on multiple LineItem
objects. Your client code would never load the LineItem
objects directly, just the Order
that contains them, which would be the aggregate root for that part of your domain.