Mastering Object-Oriented Python - Second Edition

Referring to objects via foreign keys

The key that we use to uniquely identify an object is its primary key. When child objects refer to a parent object, we have additional design decisions to make. How do we structure the children's primary keys? There are two common design strategies for child keys, based on the kind of dependence that exists between the classes of objects:

• "Child:cid": We can use this when we have children that can exist independently of an owning parent. For example, an item on an invoice refers to a product; the product can exist even if there's no invoice item for the product.
• "Parent:pid:Child:cid": We can use this when the child cannot exist without a parent. A customer address doesn't exist without a customer to ...