How would you implement 'default address' behavior in forms and APIs?

How would you implement 'default address' behavior in forms and APIs?

• A. Always assign a global default address for all users.
• B. Allow per-user/contact default, apply a system rule when not provided, and expose endpoints to set/update the default.
• C. Do not allow default addresses; require input every time.
• D. Use an external service to decide default automatically with no user control.

Answer: (B)

Default address handling should empower the user to designate which address is used by default, while the system provides a safe fallback when none is supplied. The best pattern is to allow per-user default, apply a system rule if no address is provided, and expose endpoints to set or update the default. This gives the user control across forms and APIs: a form can pre-fill the default address, API calls that omit an address can automatically use the default, and users can change their default at any time through the dedicated endpoints. From a data standpoint, store a single default per user and ensure updates are atomic so the previous default is unset when a new one is chosen; handle deletions gracefully by promoting another address or requiring a new default if none remain. This approach avoids the rigidity of a global default, keeps user preferences intact, and avoids outsourcing control to an external service.