modular-ddd

modular-ddd

Status — placeholder. Scaffolded; deep content to be written. For the working methodology today, use modular-monolith — this skill is one tool in its toolbox.

Problem

DDD tactical patterns are tools. Used where invariants live, they protect the domain from corruption and concentrate change. Used where the data is CRUD-shaped, they are bureaucracy: a ResidentAggregate whose only invariant is "field is non-null" is a class that does the same thing as an EF Core entity, more slowly, with more code, and with worse tooling. The job of this skill is to tell the two cases apart and call each by the right name.

The decision is per-module, sometimes per-feature. A module can be aggregate-rooted at its core and have CRUD-shaped peripheral features. Most real designs are mixed; treating every module as fully DDD or fully CRUD loses information.

Audience

Engineers on .NET 10 deciding the internal shape of a module after the topology has been drawn (modular-design) and the cross-module language has been aligned (modular-shared-language).

Inputs (planned)

• Module list from modular-design.
• Shared-language map from modular-shared-language.
• The invariants the business cares about (often surfaced by interviewing the SME or reading existing validation rules).

Outputs (planned)

• Per-module shape decision: aggregate-rooted, service-with-records, or thin-pass-through.
• For aggregate-rooted modules: aggregate boundary, root entity, invariants, domain events emitted.
• For service-with-records modules: the EF Core entities, the application services, the request handlers.
• An explicit list of refused DDD patterns and the reason for each refusal.

Sections to be written

• Three module shapes — aggregate-rooted, service-with-records, thin-pass-through
• When an aggregate is earned — three signs you need one, three signs you don't
• Value objects in C# 14 — record struct, equality, validation in the constructor, IParsable<T>
• Domain events as the in-tenant cross-module dispatch (links to discriminator in orchestrator)
• Specifications and the query-shape question — when to use, when IQueryable is enough
• Anti-corruption layers — when, where, how (relates to modular-shared-language)
• Refusing DDD where it does not earn rent — concrete examples
• Worked example: an aggregate-rooted Compliance module side-by-side with a service-with-records Notes module

See also

• modular-monolith — orchestrator; this skill is one tool in its toolbox
• modular-shared-language — feeds this skill the term map that decides where ACLs live
• modular-vertical-slice — organizes features inside the shape this skill decides
• modular-ddd-classifier — uses this skill's vocabulary to label legacy code