Data Class

Apply refactorings

Symptom

A class whose surface is only getters and setters; all real behavior lives in consumers, scattered across files the agent must locate to reason about anything domain-meaningful.

Goal

Behavior that belongs with the data lives on the class; the agent loading the class finds the operations and invariants it expects, in one place.

Smellier version

class Address { street; city; zip; }
function format(a) {
  return `${a.street}, ${a.city} ${a.zip}`;
}

Fresher version

class Address {
  format() {
    return `${this.street}, ${this.city} ${this.zip}`;
  }
}

Example source: Illustrative example written for this site, not a quotation from any source.

Pressure

Domain logic scatters across consumers; the agent must search the codebase to find any operation; class invariants aren't enforced so the agent must defensively check them at every consumer.

Tradeoff

Migrating behavior onto the class can pull new collaborators into its definition; consumers shrink but the class's surface grows and its dependencies multiply.

Relief

Invariants are enforceable in one place; the agent reasons about the class as a real domain object instead of chasing operations across consumers.

Trap

Attaching every operation that touches the data — including ones that belong to use cases or services — turns the data class into a god object the agent must load to reason about anything in the surrounding domain.