113 lines
4.7 KiB
ReStructuredText
113 lines
4.7 KiB
ReStructuredText
Spiff Extensions
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================
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BPMN Model
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----------
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We'll be using the following files from `spiff-example-cli <https://github.com/sartography/spiff-example-cli>`_.
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- `bpmn-spiff/events <https://github.com/sartography/spiff-example-cli/blob/master/bpmn-spiff/events.bpmn>`_ workflow
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- `bpmn-spiff/call activity <https://github.com/sartography/spiff-example-cli/blob/master/bpmn-spiff/call_activity.bpmn>`_ workflow
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- `product_prices <https://github.com/sartography/spiff-example-cli/blob/master/bpmn/product_prices.dmn>`_ DMN table
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- `shipping_costs <https://github.com/sartography/spiff-example-cli/blob/master/bpmn/shipping_costs.dmn>`_ DMN table
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We'll also be using the `run-spiff.py <https://github.com/sartography/spiff-example-clie/blob/master/run-spiff.py>`_ script
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instead of the `run.py <https://github.com/sartography/spiff-example-clie/blob/master/run.py>`_ script
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Camunda's BPMN editor does not handle data objects in the expected way. You can create data object
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references, but there is no way to re-use data objects.
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It also does not support Message Correlations, and the interface for generating a message payload doesn't work
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well in a Python environment.
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We have extended BPMN.js to correct some of these issues. The examples in this section were created using our
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custom BPMN editor, `bpmn-js-spiffworkflow <https://github.com/sartography/bpmn-js-spiffworkflow>`_.
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Data Objects
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^^^^^^^^^^^^
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Data objects exist at a process level and are not visible in the diagram, but when you create a data object
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reference, you can choose what data object it points to.
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.. figure:: figures/data_object_configuration.png
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:scale: 50%
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:align: center
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Configuring a data object reference
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When a data output association (a line) is drawn from a task to a data object reference, the value is copied
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from the task data to the workflow data and removed from the task. If a data input association is created from
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a data object reference, the value is temporarily copied into the task data while the task is being executed,
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and immediate removed afterwards.
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This allows sensitive data to be removed from individual tasks (in our example, the customer's credit card
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number). It can also be used to prevent large objects from being repeatedly copied from task to task.
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Multiple data object references can point to the same underlying data. In our example, we use to references
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to the same data object to pass the credit card info to both tasks that require it. On the right panel, we can
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see that only one data object exists in the process.
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.. figure:: figures/data_objects.png
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:scale: 30%
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:align: center
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Data objects in a process
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If you step through this workflow, you'll see that the card number is not contained in the task data after
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the 'Enter Payment Info' has been completed.
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Configuring Messages
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^^^^^^^^^^^^^^^^^^^^
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Messages are handled slightly differently in Spiff Message Events. On a Message Throw Event or Send Task,
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we define a payload, which is simply a bit of python code that will be evaluated against the task data and
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sent along with the message. In the corresponding Message Catch Event or Receive Task, we define a
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variable name where we'll store the result.
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Spiff Messages can also optionally use correlation keys. The correlation key is an expression or set of
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expressions that are evaluated against a message payload to create an additional identifier for associating
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messages with processes.
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In our example, it is possible that multiple QA processes could be started (the timer event will fire every
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minute until the order fulfillment process is complete). In this case, the message name is insufficient, as
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there will be multiple processes that can accept messages based on the name.
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.. figure:: figures/correlation.png
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:scale: 50%
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:align: center
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Defining a correlation key
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We use the timestamp of the message creation as a unique key that can be used to distinguish between multiple
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QA processes.
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.. figure:: figures/spiff_message_throw.png
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:scale: 50%
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:align: center
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Configuring a message throw event
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When we receive the event, we assign the payload to :code:`order_info`.
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.. figure:: figures/spiff_message_catch.png
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:scale: 50%
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:align: center
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Configuring a message catch event
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The correlation is visible on both the Throw and Catch Events, but it is associated with the message rather
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than the tasks themselves; if you update the expression on either event, the changes will appear in both places.
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Running The Model
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^^^^^^^^^^^^^^^^^
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If you have set up our example repository, this model can be run with the
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following command:
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.. code-block:: console
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./run-spiff.py -p order_product \
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-d bpmn/product_prices.dmn bpmn/shipping_costs.dmn \
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-b bpmn-spiffevents.bpmn bpmn-spiff/call_activity.bpmn
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