django-fsm adds simple declarative state management for django models.
Important
Django FSM-2 started as a fork of Django FSM.
Big thanks to Mikhail Podgurskiy for starting this awesome project and maintaining it for so many years.
Unfortunately, development has stalled for almost 2 years and it was officially announced there will be no new releases. Viewflow is presented as an alternative but the transition is not that easy.
If what you need is just a simple state machine, tailor-made for Django, Django FSM-2 is the successor of Django FSM, with dependencies updates, typing (planned)
FSM really helps to structure the code, and centralize the lifecycle of your Models.
Instead of adding a CharField field to a django model and manage its
values by hand everywhere, FSMFields offer the ability to declare your
transitions once with the decorator. These methods could contain side-effects, permissions, or logic to make the lifecycle management easier.
Nice introduction is available here: https://gist.github.com/Nagyman/9502133
$ pip install django-fsm-2Or, for the latest git version
$ pip install -e git://github.com/django-commons/django-fsm-2.git#egg=django-fsmAdd FSMState field to your model
from django_fsm import FSMField, transition
class BlogPost(models.Model):
state = FSMField(default='new')Use the transition decorator to annotate model methods
@transition(field=state, source='new', target='published')
def publish(self):
"""
This function may contain side-effects,
like updating caches, notifying users, etc.
The return value will be discarded.
"""The field parameter accepts both a string attribute name or an actual
field instance.
If calling publish() succeeds without raising an exception, the state field will be changed, but not written to the database.
from django_fsm import can_proceed
def publish_view(request, post_id):
post = get_object_or_404(BlogPost, pk=post_id)
if not can_proceed(post.publish):
raise PermissionDenied
post.publish()
post.save()
return redirect('/')If some conditions are required to be met before changing the state, use
the conditions argument to transition. conditions must be a list
of functions taking one argument, the model instance. The function must
return either True or False or a value that evaluates to True or
False. If all functions return True, all conditions are considered
to be met and the transition is allowed to happen. If one of the
functions returns False, the transition will not happen. These
functions should not have any side effects.
You can use ordinary functions
def can_publish(instance):
# No publishing after 17 hours
if datetime.datetime.now().hour > 17:
return False
return TrueOr model methods
def can_destroy(self):
return self.is_under_investigation()Use the conditions like this:
@transition(field=state, source='new', target='published', conditions=[can_publish])
def publish(self):
"""
Side effects galore
"""
@transition(field=state, source='*', target='destroyed', conditions=[can_destroy])
def destroy(self):
"""
Side effects galore
"""You can instantiate a field with protected=True option to prevent
direct state field modification.
class BlogPost(models.Model):
state = FSMField(default='new', protected=True)
model = BlogPost()
model.state = 'invalid' # Raises AttributeErrorNote that calling refresh_from_db on a model instance with a protected FSMField will cause an exception.
source parameter accepts a list of states, or an individual state or
django_fsm.State implementation.
You can use * for source to allow switching to target from any
state.
You can use + for source to allow switching to target from any
state excluding target state.
target state parameter could point to a specific state or
django_fsm.State implementation
from django_fsm import FSMField, transition, RETURN_VALUE, GET_STATE
@transition(field=state,
source='*',
target=RETURN_VALUE('for_moderators', 'published'))
def publish(self, is_public=False):
return 'for_moderators' if is_public else 'published'
@transition(
field=state,
source='for_moderators',
target=GET_STATE(
lambda self, allowed: 'published' if allowed else 'rejected',
states=['published', 'rejected']))
def moderate(self, allowed):
pass
@transition(
field=state,
source='for_moderators',
target=GET_STATE(
lambda self, **kwargs: 'published' if kwargs.get("allowed", True) else 'rejected',
states=['published', 'rejected']))
def moderate(self, allowed=True):
passCustom properties can be added by providing a dictionary to the custom
keyword on the transition decorator.
@transition(field=state,
source='*',
target='onhold',
custom=dict(verbose='Hold for legal reasons'))
def legal_hold(self):
"""
Side effects galore
"""If the transition method raises an exception, you can provide a specific target state
@transition(field=state, source='new', target='published', on_error='failed')
def publish(self):
"""
Some exception could happen here
"""Instead of passing a two-item iterable choices you can instead use the
three-element state_choices, the last element being a string reference
to a model proxy class.
The base class instance would be dynamically changed to the corresponding Proxy class instance, depending on the state. Even for queryset results, you will get Proxy class instances, even if the QuerySet is executed on the base class.
Check the test case for example usage. Or read about implementation internals
It is common to have permissions attached to each model transition.
django-fsm handles this with permission keyword on the transition
decorator. permission accepts a permission string, or callable that
expects instance and user arguments and returns True if the user can
perform the transition.
@transition(field=state, source='*', target='published',
permission=lambda instance, user: not user.has_perm('myapp.can_make_mistakes'))
def publish(self):
pass
@transition(field=state, source='*', target='removed',
permission='myapp.can_remove_post')
def remove(self):
passYou can check permission with has_transition_permission method
from django_fsm import has_transition_perm
def publish_view(request, post_id):
post = get_object_or_404(BlogPost, pk=post_id)
if not has_transition_perm(post.publish, request.user):
raise PermissionDenied
post.publish()
post.save()
return redirect('/')get_all_FIELD_transitions Enumerates all declared transitions
get_available_FIELD_transitions Returns all transitions data available
in current state
get_available_user_FIELD_transitions Enumerates all transitions data
available in current state for provided user
If you store the states in the db table you could use FSMKeyField to ensure Foreign Key database integrity.
In your model :
class DbState(models.Model):
id = models.CharField(primary_key=True, max_length=50)
label = models.CharField(max_length=255)
def __unicode__(self):
return self.label
class BlogPost(models.Model):
state = FSMKeyField(DbState, default='new')
@transition(field=state, source='new', target='published')
def publish(self):
passIn your fixtures/initial_data.json :
[
{
"pk": "new",
"model": "myapp.dbstate",
"fields": {
"label": "_NEW_"
}
},
{
"pk": "published",
"model": "myapp.dbstate",
"fields": {
"label": "_PUBLISHED_"
}
}
]Note : source and target parameters in @transition decorator use pk values of DBState model as names, even if field "real" name is used, without _id postfix, as field parameter.
You can also use FSMIntegerField. This is handy when you want to use
enum style constants.
class BlogPostStateEnum(object):
NEW = 10
PUBLISHED = 20
HIDDEN = 30
class BlogPostWithIntegerField(models.Model):
state = FSMIntegerField(default=BlogPostStateEnum.NEW)
@transition(field=state, source=BlogPostStateEnum.NEW, target=BlogPostStateEnum.PUBLISHED)
def publish(self):
passdjango_fsm.signals.pre_transition and
django_fsm.signals.post_transition are called before and after allowed
transition. No signals on invalid transition are called.
Arguments sent with these signals:
sender The model class.
instance The actual instance being processed
name Transition name
source Source model state
target Target model state
django-fsm provides optimistic locking mixin, to avoid concurrent
model state changes. If model state was changed in database
django_fsm.ConcurrentTransition exception would be raised on
model.save()
from django_fsm import FSMField, ConcurrentTransitionMixin
class BlogPost(ConcurrentTransitionMixin, models.Model):
state = FSMField(default='new')For guaranteed protection against race conditions caused by concurrently executed transitions, make sure:
- Your transitions do not have any side effects except for changes in the database,
- You always run the save() method on the object within
django.db.transaction.atomic()block.
Following these recommendations, you can rely on ConcurrentTransitionMixin to cause a rollback of all the changes that have been executed in an inconsistent (out of sync) state, thus practically negating their effect.
Renders a graphical overview of your models states transitions
You need pip install "graphviz>=0.4" library and add django_fsm to
your INSTALLED_APPS:
INSTALLED_APPS = (
...
'django_fsm',
...
)# Create a dot file
$ ./manage.py graph_transitions > transitions.dot
# Create a PNG image file only for specific model
$ ./manage.py graph_transitions -o blog_transitions.png myapp.BlogYou may also take a look at django-fsm-2-admin project containing a mixin and template tags to integrate django-fsm-2 state transitions into the django admin.
https://github.com/coral-li/django-fsm-2-admin
Transition logging support could be achieved with help of django-fsm-log package