Lets suppose there's a database schema defined like this:
Person.mail_address_key ----- Address.address_key Person.billing_address_key ----- Address.address_key
Person has a mailing address and a billing address. As a denormalization technique, we create a separate
Address table. Most of the time the
mail_address_key and the
billing_address_key of a single
Person will be the same value (ie: their mailing and billing address key will be the same).
In my database the
Address has an identity (the address key). But, in my domain model, I don't see a compelling reason for the
Address to be an Entity, I'd like it to be a Value Object.
- In DDD, is this an option? Or are Value Objects usually a group of columns (as opposed to a table)? I'm kind of playing the devil's advocate here, because I don't think the database should dictate the domain model structure, but just making sure.
- If so, where/when/how does the address lose its database identity so it can be used as a Value Object in the Domain Layer? Or, am I supposed to keep the database identifier in the Value Object?
- When the model needs to be persisted in the database, what's the process? Am I supposed to go through a process of a) Find an address by these fields, b) if it doesn't exist, create a new one c) if it does, update the fields?