Value Objects vs Entities in DDD

In Domain-Driven Design (DDD), Value Objects and Entities are two fundamental building blocks used to model the domain.

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Value Object

A Value Object represents a descriptive aspect of the domain that does not have a unique identity. Its meaning comes from its attributes, not from any kind of identifier. Think of it as a value that is defined by its content.

• Immutable: Once created, you don’t change a Value Object. Instead, you replace it.
• No identity: Two Value Objects with the same data are considered the same.
• Examples:
  • A money amount (like $20.00)
  • A date range
  • An address (e.g., “123 Main St, New York”)

They are useful when you want to describe something and focus on what it is, not who it is.

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Entity

An Entity is an object that has a distinct identity that runs through time and different states. Even if its data changes, the identity remains the same.

• Has an identity: Usually represented by a unique ID (like a user ID or order number).
• Mutable: Its properties can change, but its identity stays constant.
• Examples:
  • A person
  • An order
  • A product in inventory

Entities are used when you care about tracking who or what something is, rather than just the values it holds.

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Quick Comparison:

Feature	Value Object	Entity
Identity	No	Yes
Equality	Based on values	Based on identity
Mutability	Usually immutable	Usually mutable
Purpose	Describes things	Tracks and distinguishes things