Aggregate design principles

Here are a few principles popularized in the DDD community about how to design Aggregates.

Rule #1 - All transactions happen against Aggregates

The Aggregate is responsible for Command decision-making logic involving a single entity. Each Entity or Value Object within an Aggregate should be related to that singular purpose: making decisions against Commands.

To decide whether we should allow the Command transaction to complete, or if we should cancel with a failed Result<T> instead requires us to have instances of all the Entities and Value Objects that belong to this Aggregate

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