Value Objects And Dtos (Symfony)

Use when

• A domain concept with rules of its own (money, email, address) travels as raw scalars.
• Data crosses a boundary: request input, API output, message payload.
• Storing a value object inside a Doctrine entity.

Default workflow

1. Decide: a value object for a domain concept with invariants, a DTO for data crossing a boundary.
2. Make it readonly, validate in the constructor, and fail fast.
3. Give value objects equality by value and operations that return new instances.
4. Persist value objects as Doctrine embeddables.
5. Keep input DTOs (validation constraints) apart from output DTOs (serializer attributes).

Guardrails

• No setters and no mutation: a change returns a new instance.
• DTOs carry data only, with no behavior.
• Never expose entities directly as API input or output.
• Store money as an integer in minor units, never as a float.