113 lines
4.1 KiB
ReStructuredText
113 lines
4.1 KiB
ReStructuredText
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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/master/bpmn/multiinstance.bpmn>`_ workflow
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- `call activity multi <https://github.com/sartography/spiff-example-cli/blob/master/bpmn/call_activity_multi.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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Suppose we want our customer to be able to select more than one product.
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If we knew how many products they would select at the beginning of the workflow, we could
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configure 'Select and Customize Product' as a Sequential MultiInstance Task. We would
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specify the name of the collection and each iteration of the task would add a new item
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to it.
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Since we can't know in advance how many products the order, we'll need to modify that
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workflow to ask them whether they want to continue shopping and maintain their product
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selections in a collection.
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.. figure:: figures/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'll also need to update our element docmentation to display all products.
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.. figure:: figures/documentation_multi.png
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:scale: 30%
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:align: center
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Updated Documentation for 'Review Order'
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.. note::
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Note that we are using a dot instead of the typical python dictionary access to obtain
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the values. Spiff automatically generates such a representation, which simplifies creating the
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documentation strings; however regular Python syntax will work as well.
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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_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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Spiff will generate a task for each of the items in the collection. Because of the way
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SpiffWorkflow manages the data for these tasks, the collection MUST be a dictionary.
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Each value in the dictionary will be copied into a variable with the name specified in
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the 'Element Variable' field, so you'll need to specify this as well.
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.. figure:: figures/multiinstance_form_configuration.png
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:scale: 30%
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:align: center
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MultiInstance form configuration
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We'll also need to update the form field id so that the results will be added to the
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item of the collection rather than the top level of the task data. This is where the
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'Element Variable' field comes in: we'll need to change `product_available` to
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`product.product_available`, because we set up `product` as our reference to the
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current item.
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.. figure:: figures/multiinstance_flow_configuration.png
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:scale: 30%
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:align: center
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Product available flow configuration
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Finally, we'll need to update our 'No' flow to check all items in the collection for
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availability.
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.. note::
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In our form configuration, we used `product.product_available` but when we reference
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it in the flow, we use the standard python dictionary syntax. We can't use that
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notation in form fields, so in this case we need to use SpiffWorkflow's dot notation
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conversion.
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Sequential MultiInstance
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^^^^^^^^^^^^^^^^^^^^^^^^
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SpiffWorkflow also supports Sequential MultiInstance Tasks for previously defined
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collections, or if the loopCardinality is known in advance, although we have not added an
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example of this to our workflow.
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For more information about MultiInstance Tasks and SpiffWorkflow, see :doc:`/bpmn/advanced`.
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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.py -p order_product \
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-d bpmn/product_prices.dmn bpmn/shipping_costs.dmn \
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-b bpmn/multiinstance.bpmn bpmn/call_activity_multi.bpmn
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