Looking for help to work out a subscription service schema

I'm finding it difficult to decide on a schema for a monthly subscription service. In particular, if my the credit cards table should be related to the customer or to the subscription.

The tables I currently have are the following:

   users
      id
      other fields.

   addresses
      id
      userid
      other fields

   subscriptions
      开发者_开发百科id
      userid
      other fields

   cards
      id
      userid
      last4digits

A user can only have one subscription. For now, only credit cards are accepted as a form of payment. However, that could change in the future. My schema is simplistic, but I'm afraid my setup will be a pain to alter in the future if more payment types are added.

Can you provide me with some advice please?

Your database design should consider what types of queries you will want to execute against the data, however, without knowing more, how about introducing a Payments table:

Clients 1..* Cards

Cards 1..* Payments

Payments 1..* Subscriptions

This way in the future you can easily add other payment types, e.g. add:

Clients 1..* PaypalAccounts

PaypalAccounts 1..* Payments

Also, I'm assuming a payment can be taken for more than one subscription.