Secure by Design

6 Ensuring integrity of state

This chapter covers

• Managing mutable states using entities
• Ensuring an entity is consistent on creation
• Ensuring an entity keeps its integrity

Mutable state is an important aspect of systems. To some degree, changing state is the point of many systems, like the online bookstore of chapter 2. The system keeps track of a variety of state changes: books are put in a shopping cart, the order is paid for, and the books are shipped to the customer. If there aren’t state changes, not much interesting happens.¹  Mutable state can be represented technically in many different ways. We’ll take a look at some alternatives and explore our preferred way—explicitly modeling mutable state in the style of Domain-Driven Design ...