Gateways

BPMN Model

In this section, we’ll expand our model by creating alternate paths through the workflow depending on the current workflow state, in this case, answers provided by the user through forms.

We’ve also added a second DMN table to find the cost of the selected shipping method, and we updated our order total calculations to incorporate that cost.

We’ll be using the following files from spiff-example-cli.

Exclusive Gateway

Exclusive Gateways are used when exactly one alternative can be selected.

Suppose our products are T-shirts and we offer product C in several colors. After the user selects a product, we check to see it if is customizable. Our default branch will be ‘Not Customizable’, but we’ll direct the user to a second form if they select ‘C’; our condition for choosing this branch is a simple python expression.

../_images/exclusive_gateway.png

Flow configuration

Parallel Gateway

IDs vs Names

We’ve assigned descriptive names to all our tasks so far. Text added to the Name field will appear in the diagram, so sometimes it’s better to leave it blank to avoid visual clutter. I’ve put a description of the gateway into the ID field instead.

Parallel Gateways are used when the subsequent tasks do not need to be completed in any particular order. The user can complete them in any sequence and the workflow will wait for all tasks to be finished before advancing.

We do not care whether the user chooses a shipping method or enters their address first, but they’ll need to complete both tasks before continuing.

We don’t need to do any particular configuration for this gateway type.

../_images/parallel_gateway.png

Parallel Gateway example

Inclusive Gateway

SpiffWorkflow also supports Inclusive Gateways, though we do not have an example of this gateway type in this tutorial. Inclusive Gateways have conditions on outgoing flows like Exclusive Gateways, but unlike Exclusive Gateways, multiple paths may be taken if more than one conition is met.

Event-Based Gateway

SpiffWorkflow supports Event-Based Gateways, though we do not use them in this tutorial. Event-Based gateways select an outgoing flow based on an event. We’ll discuss events in the next section.

Running The Model

If you have set up our example repository, this model can be run with the following command:

./spiff-bpmn-runner.py -p order_product \
     -d bpmn/tutorial/product_prices.dmn bpmn/tutorial/shipping_costs.dmn \
     -b bpmn/tutorial/gateway_types.bpmn