Common one-to-many table for multiple entities

Question

Suppose I have two tables, Customer and Vendor. I want to have a common address table for customer and vendor addresses. Customers and Vendors can both have one to many ad

Answer 1

I think out of the three options you gave, I'd be most inclined to go with option 1. Normally a customer or vendor won't have more than a few different addresses, but if they do, maybe the solution below would work better for you. I wouldn't go for option 2, because it probably doesn't make sense to associate an Address with both a Customer and a Vendor at the same time. I know you'd probably only set one of those IDs at a time, but the model might be confusing, and you may need to add special logic to make sure only the CustomerID or the VendorID is set on any given record. I would definitely not do option 3, because you can't make FKID a true FK. If you want a column to reference more than one table, you will not be able to use a FK constraint in the database to enforce it. Plus, if you plan on using an ORM to interact with the database in code, they tend to have trouble dealing with "fake" foreign keys that reference multiple tables depending on a separate "discriminator" column.

If you want a truly open-ended solution, you could create many-to-many relationships between Customer and Address and Vendor and Address.

Customer
--------
CustomerID (PK)

Vendor
------
VendorID (PK)

Address
-------
AddressID (PK)

CustomerAddress
---------------
CustomerID (FK/PK)
AddressID (FK/PK)

VendorAddress
-------------
VendorID (FK/PK)
AddressID (FK/PK)