Functions

Functions are the description in Python of what you want to do on certain events happen. So you define them once and you can use them with multiple hooking up. Just go to /admin/river/function/ admin page and create your functions there.``django-river`` function admin support python code highlighting as well if you enable the codemirror2 app. Don’t forget to collect statics for production deployments.

INSTALLED_APPS=[
    ...
    codemirror2
    river
    ...
]

Here is an example function;

from datetime import datetime

def handle(context):
    print(datetime.now())

Important: YOUR FUNCTION SHOULD BE NAMED AS handle. Otherwise django-river won’t execute your function.

Context Parameter

django-river will pass a context down to your function in order for you to know why the function is triggered or for which object or so. And the context will look different for different type of events. But it also has some common parts for all the events. Let’s look at how it looks;

context.hook ->>

Key	Type	Format	Description
type	String	* on-approved * on-transit * on-complete	The event type that is hooked up. The payload will likely differ according to this value
when	String	* BEFORE * AFTER	Whether it is hooked right before the event happens or right after
payload	dict		This is the context content that will differ for each event type. The information that can be gotten from payload is describe in the table below

Context Payload

On-Approved Event Payload

Key	Type	Description
workflow	Workflow Model	The workflow that the transition currently happening
workflow_object	Your Workflow Object	The workflow object of the model that has the state field in it
transition_approval	Transition Approval	The approval object that is currently approved which contains the information of the transition(meta) as well as who approved it etc.

On-Transit Event Payload

Key	Type	Description
workflow	Workflow Model	The workflow that the transition currently happening
workflow_object	Your Workflow Object	The workflow object of the model that has the state field in it
transition_approval	Transition Approval	The last transition approval object which contains the information of the transition(meta) as well as who last approved it etc.

On-Complete Event Payload

Key	Type	Description
workflow	Workflow Model	The workflow that the transition currently happening
workflow_object	Your Workflow Object	The workflow object of the model that has the state field in it

Example Function

from river.models.hook import BEFORE, AFTER

def _handle_my_transitions(hook):
    workflow = hook['payload']['workflow']
    workflow_object = hook['payload']['workflow_object']
    source_state = hook['payload']['transition_approval'].meta.transition_meta.source_state
    destination_state = hook['payload']['transition_approval'].meta.transition_meta.destination_state
    last_approved_by = hook['payload']['transition_approval'].transactioner
    if hook['when'] == BEFORE:
        print('A transition from %s to %s will soon happen on the object with id:%s and field_name:%s!' % (source_state.label, destination_state.label, workflow_object.pk, workflow.field_name))
    elif hook['when'] == AFTER:
        print('A transition from %s to %s has just happened on the object with id:%s and field_name:%s!' % (source_state.label, destination_state.label, workflow_object.pk, workflow.field_name))
    print('Who approved it lately is %s' % last_approved_by.username)

def _handle_my_approvals(hook):
    workflow = hook['payload']['workflow']
    workflow_object = hook['payload']['workflow_object']
    approved_by = hook['payload']['transition_approval'].transactioner
    if hook['when'] == BEFORE:
        print('An approval will soon happen by %s on the object with id:%s and field_name:%s!' % ( approved_by.username, workflow_object.pk, workflow.field_name ))
    elif hook['when'] == AFTER:
        print('An approval has just happened by %s  on the object with id:%s and field_name:%s!' % ( approved_by.username, workflow_object.pk, workflow.field_name ))

def _handle_completions(hook):
    workflow = hook['payload']['workflow']
    workflow_object = hook['payload']['workflow_object']
    if hook['when'] == BEFORE:
        print('The workflow will soon be complete for the object with id:%s and field_name:%s!' % ( workflow_object.pk, workflow.field_name ))
    elif hook['when'] == AFTER:
        print('The workflow has just been complete for the object with id:%s and field_name:%s!' % ( workflow_object.pk, workflow.field_name ))

def handle(context):
    hook = context['hook']
    if hook['type'] == 'on-transit':
        _handle_my_transitions(hook)
    elif hook['type'] == 'on-approved':
        _handle_my_approvals(hook)
    elif hook['type'] == 'on-complete':
        _handle_completions(hook)
    else:
        print("Unknown event type %s" % hook['type'])