# Implementing Domain-Driven Design vs Refactoring.Guru

Status: reviewed
Research basis: mini-only

Verdict: ✅ Complementary

Conflict: 12%
Overlap: 38%
Complementarity: 78%

## Loading Decision

Use together when changing existing code: one rule set controls safe change sequencing while the other defines the target design, construction, architecture, data, or production quality.

## Book A Pressure

- Implementing Domain-Driven Design should drive tasks where DDD implementation choices around contexts, aggregates, repositories, events, services, and translations dominate.
- Evidence: `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 3-5: applies when DDD implementation choices affect contexts, language, aggregates, repositories, events, application services, package structure, or cross-context integration.

## Book B Pressure

- Refactoring.Guru should drive tasks where smell diagnosis, smallest treatment choice, behavior verification, and stop conditions dominate.
- Evidence: `refactoring-guru/refactoring-guru.mini.md` lines 3-5: applies when code smells, technique choice, behavior preservation, and cleanup scope control matter.

## Complementary Forces

- Claim: Implementing Domain-Driven Design contributes implementation-level DDD pressure around contexts, aggregates, repositories, events, services, and translation; Refactoring.Guru contributes smell-diagnosis, smallest-treatment, behavior-verification, and stop-condition pressure. Together they are useful only where both scopes are active.
- Evidence:
  - `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 13-31: requires context-first interpretation, consistent local language, Core Domain protection, explicit context interactions and translations, small invariant-driven Aggregates with identity references, Entities/Value Objects/Domain Services/Repositories/Domain Events/Event Sourcing/Application Services by rule, Bounded Context modules, DTO/projection/query separation, CQRS where justified, model-walk code generation, and direct domain/boundary tests.
  - `refactoring-guru/refactoring-guru.mini.md` lines 13-37: requires separating behavior changes, diagnosing smell/cost/scope/end state/verification/stop condition, smallest treatment first, runnable small transformations, checks after risky moves, Rule of Three, debt paid by current cost, smell categories, bloaters/switch/change/coupler/dispensable treatments, comments vs code fixes, behavior with data, no getter/setter-only encapsulation, no speculative abstractions, public compatibility, extraction/movement/condition/data/generalization prechecks, and deliberate exceptions.

## Overlap

- Claim: They overlap where both affect safe existing-code change, tests, behavior preservation, ownership, and stopping before speculative cleanup; the overlap score reflects how often an agent would receive similar pressure from both.
- Evidence:
  - `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 48-57: checks explicit context, consistent local terms, protected Core Domain, visible translations, small invariant-driven Aggregates, behavior-bearing Entities/Value Objects, aggregate-root repositories, meaningful events/event sourcing only when right, coordinating application services, and external representations outside the domain.
  - `refactoring-guru/refactoring-guru.mini.md` lines 57-64: checks work type, diagnosed smell/cost, smallest treatment, behavior preservation, smell reduction, no speculative pattern use, public/state/ownership checks, and documented untreated smells.

## Conflicts

- Claim: The tension is scope creep: design or architecture improvements must not override behavior preservation, characterization, or the current-smell stop condition.
- Evidence:
  - `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 7-9: corrects renamed CRUD by requiring operational domain modeling inside an explicit context with local language, small invariant boundaries, identity references, and translation.
  - `refactoring-guru/refactoring-guru.mini.md` lines 7-9: corrects treating refactoring as general cleanup or pattern application instead of smell-driven treatment with verification and stop condition.

## Use Together When

- Use together when existing code must be reshaped toward Implementing Domain-Driven Design goals without changing observable behavior or turning cleanup into redesign.

## Prefer One When

- Prefer the refactoring rule set when observable behavior must stay unchanged; prefer the other book when designing new behavior rather than reshaping existing structure.

## Source Basis

- `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 3-5: applies when DDD implementation choices affect contexts, language, aggregates, repositories, events, application services, package structure, or cross-context integration.
- `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 7-9: corrects renamed CRUD by requiring operational domain modeling inside an explicit context with local language, small invariant boundaries, identity references, and translation.
- `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 13-31: requires context-first interpretation, consistent local language, Core Domain protection, explicit context interactions and translations, small invariant-driven Aggregates with identity references, Entities/Value Objects/Domain Services/Repositories/Domain Events/Event Sourcing/Application Services by rule, Bounded Context modules, DTO/projection/query separation, CQRS where justified, model-walk code generation, and direct domain/boundary tests.
- `implementing-domain-driven-design/implementing-domain-driven-design.mini.md` lines 48-57: checks explicit context, consistent local terms, protected Core Domain, visible translations, small invariant-driven Aggregates, behavior-bearing Entities/Value Objects, aggregate-root repositories, meaningful events/event sourcing only when right, coordinating application services, and external representations outside the domain.
- `refactoring-guru/refactoring-guru.mini.md` lines 3-5: applies when code smells, technique choice, behavior preservation, and cleanup scope control matter.
- `refactoring-guru/refactoring-guru.mini.md` lines 7-9: corrects treating refactoring as general cleanup or pattern application instead of smell-driven treatment with verification and stop condition.
- `refactoring-guru/refactoring-guru.mini.md` lines 13-37: requires separating behavior changes, diagnosing smell/cost/scope/end state/verification/stop condition, smallest treatment first, runnable small transformations, checks after risky moves, Rule of Three, debt paid by current cost, smell categories, bloaters/switch/change/coupler/dispensable treatments, comments vs code fixes, behavior with data, no getter/setter-only encapsulation, no speculative abstractions, public compatibility, extraction/movement/condition/data/generalization prechecks, and deliberate exceptions.
- `refactoring-guru/refactoring-guru.mini.md` lines 57-64: checks work type, diagnosed smell/cost, smallest treatment, behavior preservation, smell reduction, no speculative pattern use, public/state/ownership checks, and documented untreated smells.

## Review Notes

- External context was not used as decisive evidence for Implementing Domain-Driven Design vs Refactoring.Guru; the verdict is based on the cited local `mini` line ranges.
