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Question

I'm building a Rails app where a User can have many Addresses . A User also needs a primary billing Address , primary shipping Address , and primary profile Address . These primary fields can point to the same Address . A User cannot have more than one of any primary Address .

I've created a join table called AddressInfo , and I'm bouncing between a few options:

1. Make 3 columns on the User model corresponding to each of the primary Address ids (this would remove the need for the join model I think).
2. Add a primary boolean column to AddressInfo , and make sure only one is true when scoped by user_id , address_id and purpose (purpose being billing , shipping or profile ).
3. Add a primary date time column to AddressInfo , and use the most recently updated as the primary address (scoped like option 2).

Maybe these options aren't the best, but it's what I've come up with so far.

Any help on how to resolve this issue would be appreciated.

UPDATE:

To be clear, once an Address is created it should always belong to that User and be undeletable. Ex. a User changes their primary billing address to a new Address : they should still be able to retrieve that old Address (maybe even make it a primary address again). If I go with option 1 and remove the join table, that means I'll need a user_id on Address .

Answer 1

Go with option 1, 3 columns. This will make less of a headache (as a programmer), will run faster, and is more flexible for doing things like combining similar addresses into one. Maybe you have 2 people with the same address, they could share the same record (not recomeneded though).

Answer 2

If you're using rails I would look to a rails solution to 'stay on the rails'.

I would consider STI ( Single Table Inheritance )
More info at Rails: Need help defining association for address table

or a Polymorphic relationship - http://guides.rubyonrails.org/association_basics.html#polymorphic-associations

As you want 1 user to have multiple address (rather than ther being multiple user types) than STI may be best for you.

Note: they can also be combined, eg http://www.archonsystems.com/devblog/2011/12/20/rails-single-table-inheritance-with-polymorphic-association/

There's a great example of STI addressing this issue at: http://blog.arkency.com/2013/07/sti/

Answer 3

Another possibility is to create another model to hold user.id, addressinfo.id, and an primary_for_address_type (containing "Shipping", "Profile", "Billing").

Constrain this to be unique on user and primary_for_address_type, and you can tag addresses in AddressInfo as being the primary for particular address types in a completely extensible way that still guarantees uniqueness of the primary address.

You might join directly from this model to address, but there's scope for getting it out of sync with your addressinfo model.