How to use the river.config.app_config.CONTENT_TYPE_CLASS function in river

(APPROVED, _('Approved')),
    (CANCELLED, _('Cancelled')),
]

LOGGER = logging.getLogger(__name__)


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)

(CANCELLED, _('Cancelled')),
    (JUMPED, _('Jumped')),
]

LOGGER = logging.getLogger(__name__)


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'))

from river.config import app_config
from river.models import BaseModel, State
from river.models.managers.workflowmetada import WorkflowManager


class Workflow(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Workflow")
        verbose_name_plural = _("Workflows")
        unique_together = [("content_type", "field_name")]

    objects = WorkflowManager()

    content_type = models.ForeignKey(app_config.CONTENT_TYPE_CLASS, verbose_name=_('Content Type'), on_delete=PROTECT)
    field_name = models.CharField(_("Field Name"), max_length=200)
    initial_state = models.ForeignKey(State, verbose_name=_("Initial State"), related_name='workflow_this_set_as_initial_state', on_delete=PROTECT)

    def natural_key(self):
        return self.content_type, self.field_name

    def __str__(self):
        return "%s.%s" % (self.content_type.model, self.field_name)

from river.models.transition import Transition

__author__ = 'ahmetdal'


@python_2_unicode_compatible
class ProceedingMeta(BaseModel):
    class Meta:
        app_label = 'river'
        verbose_name = _("Proceeding Meta")
        verbose_name_plural = _("Proceeding Metas")
        unique_together = [('content_type', 'transition', 'order')]

    objects = ProceedingMetaManager()

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

    transition = models.ForeignKey(Transition, verbose_name=_('Transition'), on_delete=CASCADE)
    permissions = models.ManyToManyField(app_config.PERMISSION_CLASS, verbose_name=_('Permissions'), blank=True)
    groups = models.ManyToManyField(app_config.GROUP_CLASS, verbose_name=_('Groups'), blank=True)
    order = models.IntegerField(default=0, verbose_name=_('Order'), null=True)
    action_text = models.TextField(_("Action Text"), max_length=200, null=True, blank=True)

    parents = models.ManyToManyField('self', verbose_name='parents', related_name='children', symmetrical=False, db_index=True, blank=True)

    def natural_key(self):
        return self.content_type, self.transition, self.order

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

(CANCELLED, _('Cancelled')),
    (DONE, _('Done')),
    (JUMPED, _('Jumped')),
]

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,