Workflows Topic Guide

One of the most challenging aspects of building a compelling user experience is crafting complex multi-part workflows. Horizon’s workflows module aims to bring that capability within everyday reach.

See also

For detailed API information refer to the Horizon Workflows.

Workflows

Workflows are complex forms with tabs, each workflow must consist of classes extending the Workflow, Step and Action

Complex example of a workflow

The following is a complex example of how data is exchanged between urls, views, workflows and templates:

1. In urls.py, we have the named parameter. E.g. resource_class_id.

   RESOURCE_CLASS = r'^(?P<resource_class_id>[^/]+)/%s$'
   
   urlpatterns = [
       url(RESOURCE_CLASS % 'update', UpdateView.as_view(), name='update')
   ]
   

2. In views.py, we pass data to the template and to the action(form) (action can also pass data to the get_context_data method and to the template).

   class UpdateView(workflows.WorkflowView):
       workflow_class = UpdateResourceClass
   
       def get_context_data(self, **kwargs):
           context = super(UpdateView, self).get_context_data(**kwargs)
           # Data from URL are always in self.kwargs, here we pass the data
           # to the template.
           context["resource_class_id"] = self.kwargs['resource_class_id']
           # Data contributed by Workflow's Steps are in the
           # context['workflow'].context list. We can use that in the
           # template too.
           return context
   
       def _get_object(self, *args, **kwargs):
           # Data from URL are always in self.kwargs, we can use them here
           # to load our object of interest.
           resource_class_id = self.kwargs['resource_class_id']
           # Code omitted, this method should return some object obtained
           # from API.
   
       def get_initial(self):
           resource_class = self._get_object()
           # This data will be available in the Action's methods and
           # Workflow's handle method.
           # But only if the steps will depend on them.
           return {'resource_class_id': resource_class.id,
                   'name': resource_class.name,
                   'service_type': resource_class.service_type}
   

3. In workflows.py we process the data, it is just more complex django form.

   class ResourcesAction(workflows.Action):
       # The name field will be automatically available in all action's
       # methods.
       # If we want this field to be used in the another Step or Workflow,
       # it has to be contributed by this step, then depend on in another
       # step.
       name = forms.CharField(max_length=255,
                              label=_("Testing Name"),
                              help_text="")
   
       def handle(self, request, data):
           pass
           # If we want to use some data from the URL, the Action's step
           # has to depend on them. It's then available in
           # self.initial['resource_class_id'] or data['resource_class_id'].
           # In other words, resource_class_id has to be passed by view's
           # get_initial and listed in step's depends_on list.
   
           # We can also use here the data from the other steps. If we want
           # the data from the other step, the step needs to contribute the
           # data and the steps needs to be ordered properly.
   
   class UpdateResources(workflows.Step):
       action_class = ResourcesAction
       # This passes data from Workflow context to action methods
       # (handle, clean). Workflow context consists of URL data and data
       # contributed by other steps.
       depends_on = ("resource_class_id",)
   
       # By contributing, the data on these indexes will become available to
       # Workflow and to other Steps (if they will depend on them). Notice,
       # that the resources_object_ids key has to be manually added in
       # contribute method first.
       contributes = ("resources_object_ids", "name")
   
       def contribute(self, data, context):
           # We can obtain the http request from workflow.
           request = self.workflow.request
           if data:
               # Only fields defined in Action are automatically
               # available for contribution. If we want to contribute
               # something else, We need to override the contribute method
               # and manually add it to the dictionary.
               context["resources_object_ids"] =\
                   request.POST.getlist("resources_object_ids")
   
           # We have to merge new context with the passed data or let
           # the superclass do this.
           context.update(data)
           return context
   
   class UpdateResourceClass(workflows.Workflow):
       default_steps = (UpdateResources,)
   
       def handle(self, request, data):
           pass
           # This method is called as last (after all Action's handle
           # methods). All data that are listed in step's 'contributes='
           # and 'depends_on=' are available here.
           # It can be easier to have the saving logic only here if steps
           # are heavily connected or complex.
   
           # data["resources_object_ids"], data["name"] and
           # data["resources_class_id"] are available here.