Domain Modeling Made Functional

The Workflow Input

Let’s start by looking at the input of the workflow.

The input to a workflow should always be a domain object (we’ll assume the input has been deserialized from a Data Transfer Object already). In our case, the object is the UnvalidatedOrder type, which we modeled earlier:

type UnvalidatedOrder = {
  OrderId : string
  CustomerInfo : UnvalidatedCustomerInfo
  ShippingAddress : UnvalidatedAddress
  ...
  }

Commands as Input

We saw at the beginning of the book that a workflow is associated with the command that initiates it. In some sense then, the real input for the workflow is not actually the order form but the command.

For the order-placing workflow, let’s call this command PlaceOrder. The command should contain everything ...