How are Value Objects stored in the database?
Solution 1:
It's ok to store Value Objects in a separate table, for the very reasons you've described. However, I think you're misunderstanding Entities vs VOs - it's not a persistence related concern.
Here's an example:
Assume that a Company and Person both have the same mail Address. Which of these statements do consider valid?
- "If I modify Company.Address, I want Person.Address to automatically get those changes"
- "If I modify Company.Address, it must not affect Person.Address"
If 1 is true, Address should be an Entity, and therefore has it's own table
If 2 is true, Address should be a Value Object. It could be stored as a component within the parent Entity's table, or it could have it's own table (better database normalisation).
As you can see, how Address is persisted has nothing to do with Entity/VO semantics.
Solution 2:
Most developers tend to think in the database first before anything else. DDD does not know about how persistence is handled. That's up to the repository to deal with that. You can persist it as an xml, sql, text file, etc etc. Entities/aggregates/value objects are concepts related to the domain.
Explanation by Vijay Patel is perfect.