DDD Domain Building Blocks

Choose the smallest DDD building block that expresses the domain rule without leaking infrastructure concerns.

Building Blocks

• Value object: identity-free, immutable, validated by construction, compared by value.

• Entity: stable identity plus lifecycle, behavior, and invariants.

• Aggregate: consistency boundary with one root.

• Domain service: stateless domain operation that does not naturally belong to one entity or value object.

• Repository: collection-like access to aggregate roots.

• Factory: creation logic that protects invariants or hides construction complexity.

• Domain event: something meaningful that happened in the domain.