144 lines
5.4 KiB
ReStructuredText
144 lines
5.4 KiB
ReStructuredText
MultiInstance Tasks
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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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- `multiinstance <https://github.com/sartography/spiff-example-cli/blob/main/bpmn/tutorial/top_level_multi.bpmn>`_ workflow
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- `call activity multi <https://github.com/sartography/spiff-example-cli/blob/main/bpmn/tutorial/call_activity_multi.bpmn>`_ workflow
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- `product_prices <https://github.com/sartography/spiff-example-cli/blob/main/bpmn/tutorial/product_prices.dmn>`_ DMN table
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- `shipping_costs <https://github.com/sartography/spiff-example-cli/blob/main/bpmntutorial//shipping_costs.dmn>`_ DMN table
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Loop Task
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^^^^^^^^^
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Suppose we want our customer to be able to select more than one product.
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We'll run our 'Select and Customize Product' Call Activity as a Loop Task.
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First we'll update the Call Activity's model to ask the customer if they would like to continue shopping.
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.. figure:: figures/multiinstance/call_activity_multi.png
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:scale: 30%
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:align: center
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Selecting more than one product
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We've also added a *postScript* to the user task. Spiffworkflow provides extensions that allow scripts to be
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run before and after tasks. It is often the case that data needs to be manipulated before and after a task.
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We could add regular Script Tasks before and after, but diagrams quickly become cluttered with scripts, and
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these extensions are intended to alleviate that.
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We use a *postScript* to add the current product to a list of products.
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.. code:: python
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products.append({
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'product_name': product_name,
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'product_quantity': product_quantity,
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'product_color': product_color,
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'product_size': product_size,
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'product_style': product_style,
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'product_price': product_price,
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})
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We'll use a *preScript* on the first User Task (Select Product and Quantity) to initialize these variables to
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:code:`None` each time we execute the task.
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Loop Tasks run either a specified number of times or until a completion condition is met. Since we can't
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know in advance how many products the customer will select, we'll add :code:`continue_shopping == 'Y'` as a
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completion condition. We'll re-run this Call Activity as long as the customer indicates they want to choose
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another product. We'll also set up the list of products that we plan on appending to.
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We also added a postscript to this activity to delete the customization values so that we won't have to
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look at them for the remainder of the workflow.
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.. figure:: figures/multiinstance/loop_task.png
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:scale: 30%
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:align: center
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Call Activity with Loop
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We also needed to update our Script Task and the Instructions of the Review Order Task to handle an array
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of products rather than a single product.
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Here is our new script
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.. code:: python
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order_total = sum([ p['product_quantity'] * p['product_price'] for p in products ]) + shipping_cost
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And our order summary
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.. code:: python
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Order Summary
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{% for product in products %}
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{{ product['product_name'] }}
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Quantity: {{ product['product_quantity'] }}
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Price: {{ product['product_price'] }}
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{% endfor %}
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Shipping Cost: {{ shipping_cost }}
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Order Total: {{ order_total }}
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Parallel MultiInstance
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^^^^^^^^^^^^^^^^^^^^^^
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We'll also update our 'Retrieve Product' Task and 'Product Not Available' flows to
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accommodate multiple products. We can use a Parallel MultiInstance for this, since
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it does not matter what order our Employee retrieves the products in.
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.. figure:: figures/multiinstance/multiinstance_task_configuration.png
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:scale: 30%
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:align: center
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MultiInstance Task configuration
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We've specified :code:`products` as our Input Collection and :code:`product` as our Input Item. The
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Input Collection should be an existing collection. We'll create a task instance for each element of
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the collection, and copy the value into the Input Item; this is how we'll access the data of the
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element.
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.. :code::
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Item: {{product['product_quantity']}} of {{product['product_name']}}
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We also specified :code:`availability` as our Output Collection. Since this variable does not exist,
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SpiffWorkflow will automatically create it. You can use an existing variable as an Output Collection;
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in this case, its contents will be updated with new values. The Output Item will be copied out of the
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child task into the Output Collection.
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The 'Retrieve Product' task creates :code:`product_available` from the form input.
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Since our input is a list, our output will also be a list. It is possible to generate different output
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types if you create the output collections before referring to them.
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We have to update our gateway condition to handle the list:
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.. figure:: figures/multiinstance/availability_flow.png
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:scale: 60%
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:align: center
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Gateway Condition
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Sequential MultiInstance
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^^^^^^^^^^^^^^^^^^^^^^^^
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SpiffWorkflow also supports Sequential MultiInstance Tasks for collections, or if the loopCardinality
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is known in advance, although we have not added an example of this to our workflow. Their configuraiton
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is almost idenitcal to the configuration for Parallel MultiInstance Tasks.
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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 following command:
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.. code-block:: console
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./spiff-bpmn-runner.py -p order_product \
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-d bpmn/tutorial/product_prices.dmn bpmn/tutorial/shipping_costs.dmn \
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-b bpmn/tutorial/top_level_multi.bpmn bpmn/tutorial/call_activity_multi.bpmn
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