Introduction

A workflow is the combination of an initial input form, used to acquire input from the user, and a list of workflow steps. For more details, see workflow architecture.

The workflow decorator takes a description, initial input form, and a target as input and turns a function into a workflow that returns a step list to be executed by the workflow engine in a workflow process. A minimal workflow looks like this:

@workflow(
    "Create product subscription",
    initial_input_form=initial_input_form_generator,
    target=Target.CREATE,
)
def create_product_subscription():
    return init >> create_subscription >> done

Information between workflow steps is passed using State, which is nothing more than a collection of key/value pairs, in Python represented by a Dict, with string keys and arbitrary values. Between steps the State is serialized to JSON and stored in the database. The step decorator is used to turn a function into a workflow step, all arguments to the step function will automatically be initialised with the value from the matching key in the State. In turn the step function will return a Dict of new and/or modified key/value pairs that will be merged into the State to be consumed by the next step. The serialization and deserialization between JSON and the indicated Python types is done automatically. A minimal workflow step looks as follows:

@step("Create subscription")
def create_subscription(
    product: UUIDstr,
    user_input: str,
) -> State:
    subscription = build_subscription(product, user_input)
    return {"subscription": subscription}

The product and user_input arguments are filled from the corresponding key/value pairs in the State, and the new subscription key/value is added to the state to be used by one of the following steps.

Every workflow starts with the builtin step init and ends with the builtin step done, with an arbitrary list of other builtin steps or custom steps in between.