How to use the river.models.Workflow function in river

LOGGER = logging.getLogger(__name__)


class Transition(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Transition")
        verbose_name_plural = _("Transitions")

    objects = TransitionApprovalManager()
    content_type = models.ForeignKey(app_config.CONTENT_TYPE_CLASS, verbose_name=_('Content Type'), on_delete=CASCADE)
    object_id = models.CharField(max_length=50, verbose_name=_('Related Object'))
    workflow_object = GenericForeignKey('content_type', 'object_id')

    meta = models.ForeignKey(TransitionMeta, verbose_name=_('Meta'), related_name="transitions", on_delete=PROTECT)
    workflow = models.ForeignKey(Workflow, verbose_name=_("Workflow"), related_name='transitions', on_delete=PROTECT)
    source_state = models.ForeignKey(State, verbose_name=_("Source State"), related_name='transition_as_source', on_delete=PROTECT)
    destination_state = models.ForeignKey(State, verbose_name=_("Destination State"), related_name='transition_as_destination', on_delete=PROTECT)

    status = models.CharField(_('Status'), choices=STATUSES, max_length=100, default=PENDING)

    iteration = models.IntegerField(default=0, verbose_name=_('Priority'))

    @property
    def next_transitions(self):
        return Transition.objects.filter(
            workflow=self.workflow,
            workflow_object=self.workflow_object,
            source_state=self.destination_state,
            iteration=self.iteration + 1
        )

def __init__(self, workflow_object, field_name):
        self.class_workflow = getattr(workflow_object.__class__.river, field_name)
        self.workflow_object = workflow_object
        self.content_type = app_config.CONTENT_TYPE_CLASS.objects.get_for_model(self.workflow_object)
        self.field_name = field_name
        self.workflow = Workflow.objects.filter(content_type=self.content_type, field_name=self.field_name).first()
        self.initialized = False

def workflow(self):
        if not self._cached_workflow:
            self._cached_workflow = Workflow.objects.filter(field_name=self.field_name, content_type=self._content_type).first()
        return self._cached_workflow

def initial_state(self):
        workflow = Workflow.objects.filter(content_type=self._content_type, field_name=self.field_name).first()
        return workflow.initial_state if workflow else None

AFTER = "AFTER"

HOOK_TYPES = [
    (BEFORE, _('Before')),
    (AFTER, _('After')),
]

LOGGER = logging.getLogger(__name__)


class Hook(BaseModel):
    class Meta:
        abstract = True

    callback_function = models.ForeignKey(Function, verbose_name=_("Function"), related_name='%(app_label)s_%(class)s_hooks', on_delete=PROTECT)
    workflow = models.ForeignKey(Workflow, verbose_name=_("Workflow"), related_name='%(app_label)s_%(class)s_hooks', on_delete=PROTECT)

    content_type = models.ForeignKey(ContentType, blank=True, null=True, on_delete=models.SET_NULL)
    object_id = models.PositiveIntegerField(blank=True, null=True)
    workflow_object = GenericForeignKey('content_type', 'object_id')

    hook_type = models.CharField(_('When?'), choices=HOOK_TYPES, max_length=50)

    def execute(self, context):
        try:
            self.callback_function.get()(context)
        except Exception as e:
            LOGGER.exception(e)

def __init__(self, workflow_object, field_name):
        self.workflow_object = workflow_object
        self.field_name = field_name
        self.workflow = getattr(self.workflow_object.river, self.field_name)
        self.status = self.workflow.on_final_state
        self.content_type = ContentType.objects.get_for_model(self.workflow_object.__class__)
        self.workflow = Workflow.objects.get(content_type=self.content_type, field_name=self.field_name)

from river.models.managers.transitionmetada import TransitionApprovalMetadataManager
from river.models.transitionmeta import TransitionMeta

__author__ = 'ahmetdal'


class TransitionApprovalMeta(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Transition Approval Meta")
        verbose_name_plural = _("Transition Approval Meta")
        unique_together = [('workflow', 'transition_meta', 'priority')]

    objects = TransitionApprovalMetadataManager()

    workflow = models.ForeignKey(Workflow, verbose_name=_("Workflow"), related_name='transition_approval_metas', on_delete=PROTECT)

    transition_meta = models.ForeignKey(TransitionMeta, verbose_name=_("Transition Meta"), related_name='transition_approval_meta', on_delete=PROTECT)

    permissions = models.ManyToManyField(app_config.PERMISSION_CLASS, verbose_name=_('Permissions'), blank=True)
    groups = models.ManyToManyField(app_config.GROUP_CLASS, verbose_name=_('Groups'), blank=True)
    priority = models.IntegerField(default=0, verbose_name=_('Priority'), null=True)
    parents = models.ManyToManyField('self', verbose_name='parents', related_name='children', symmetrical=False, db_index=True, blank=True)

    def __str__(self):
        return 'Transition: %s,Permissions: %s, Groups: %s, Order: %s' % (
            self.transition_meta,
            ','.join(self.permissions.values_list('name', flat=True)),
            ','.join(self.groups.values_list('name', flat=True)), self.priority)


def post_save_model(sender, instance, *args, **kwargs):

class TransitionApproval(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Transition Approval")
        verbose_name_plural = _("Transition Approvals")

    objects = TransitionApprovalManager()

    content_type = models.ForeignKey(app_config.CONTENT_TYPE_CLASS, verbose_name=_('Content Type'), on_delete=CASCADE)

    object_id = models.CharField(max_length=50, verbose_name=_('Related Object'))
    workflow_object = GenericForeignKey('content_type', 'object_id')

    meta = models.ForeignKey(TransitionApprovalMeta, verbose_name=_('Meta'), related_name="transition_approvals", null=True, blank=True, on_delete=SET_NULL)
    workflow = models.ForeignKey(Workflow, verbose_name=_("Workflow"), related_name='transition_approvals', on_delete=PROTECT)

    transition = models.ForeignKey(Transition, verbose_name=_("Transition"), related_name='transition_approvals', on_delete=PROTECT)

    transactioner = models.ForeignKey(app_config.USER_CLASS, verbose_name=_('Transactioner'), null=True, blank=True, on_delete=SET_NULL)
    transaction_date = models.DateTimeField(null=True, blank=True)

    status = models.CharField(_('Status'), choices=STATUSES, max_length=100, default=PENDING)

    permissions = models.ManyToManyField(app_config.PERMISSION_CLASS, verbose_name=_('Permissions'))
    groups = models.ManyToManyField(app_config.GROUP_CLASS, verbose_name=_('Groups'))
    priority = models.IntegerField(default=0, verbose_name=_('Priority'))

    previous = TreeOneToOneField("self", verbose_name=_('Previous Transition'), related_name="next_transition", null=True, blank=True, on_delete=CASCADE)

    @property
    def peers(self):

class TransitionApproval(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Transition Approval")
        verbose_name_plural = _("Transition Approvals")

    objects = TransitionApprovalManager()

    content_type = models.ForeignKey(app_config.CONTENT_TYPE_CLASS, verbose_name=_('Content Type'), on_delete=CASCADE)

    object_id = models.CharField(max_length=50, verbose_name=_('Related Object'))
    workflow_object = GenericForeignKey('content_type', 'object_id')

    meta = models.ForeignKey(TransitionApprovalMeta, verbose_name=_('Meta'), related_name="transition_approvals", null=True, blank=True, on_delete=SET_NULL)
    workflow = models.ForeignKey(Workflow, verbose_name=_("Workflow"), related_name='transition_approvals', on_delete=PROTECT)

    source_state = models.ForeignKey(State, verbose_name=_("Source State"), related_name='transition_approvals_as_source', on_delete=PROTECT)
    destination_state = models.ForeignKey(State, verbose_name=_("Next State"), related_name='transition_approvals_as_destination', on_delete=PROTECT)

    transactioner = models.ForeignKey(app_config.USER_CLASS, verbose_name=_('Transactioner'), null=True, blank=True, on_delete=SET_NULL)
    transaction_date = models.DateTimeField(null=True, blank=True)

    status = models.CharField(_('Status'), choices=STATUSES, max_length=100, default=PENDING)

    skipped = models.BooleanField(_('Skip'), default=False)

    permissions = models.ManyToManyField(app_config.PERMISSION_CLASS, verbose_name=_('Permissions'))
    groups = models.ManyToManyField(app_config.GROUP_CLASS, verbose_name=_('Groups'))
    priority = models.IntegerField(default=0, verbose_name=_('Priority'))

    enabled = models.BooleanField(_('Enabled?'), default=True)