State Machines

Modeling Workflows with Explicit State Transitions

Many business objects have a lifecycle. An order may be created, approved, fulfilled, or cancelled. A support ticket may be open, assigned, resolved, or reopened. Problems begin when those lifecycle rules are represented only by a status field and scattered if statements. As the system grows, different code paths can start disagreeing about which changes are legal. One handler allows a cancelled order to be approved, another silently ignores the request, and a third checks a different set of statuses. The status values are visible, but the rules connecting them are not.