Value Object

Kind: pattern

Layer: Domain Modeling

Record: architecture:value-object

Severity: recommended

Scope: domain, modeling, immutability

Canonical: Ontology

A design pattern that models a domain value as an immutable, self-validating object compared by its attributes.

Listed in Architecture principles, after Aggregate and before Entity.

Requires

• Value Equality

Reinforces

• Immutability
• Encapsulation

Enables

• Self-Validating Values
• Side-Effect-Free Equality

Conflicts with

• Primitive Obsession
• Data Clumps
• Long Parameter List

In tension with

• Object Count
• Entity
• Entity / Value Object

Tensions

• Value Object / Object Count

Violated by

• Primitive Obsession

Severity

• recommended

Category

• Domain Architecture

Refactors

• Anemic Domain Model
• Utility Dump
• Domain Model
• Intent-Revealing Interface

Linked from

• Anti-patterns
• Domain Architecture
• Correctness / Determinism / Verification
• Core Modular Design
• Schema / Canonical Data / Semantics
• Domain Architecture
• Severity levels
• The resolutions