Django friendly finite state machine support
django-fsm adds declarative states management for django models.
Instead of adding some state field to a django model, and manage it
values by hand, you could use FSMState field and mark model methods
transition decorator. Your method will contain the side-effects
of the state change.
The decorator also takes a list of conditions, all of which must be met before a transition is allowed.
$ pip install django-fsm
Or, for the latest git version
$ pip install -e git://github.com/kmmbvnr/django-fsm.git#egg=django-fsm
Library have Python 3 support, except graph transition drawing, b/c pygraphviz is not ported yet.
Add FSMState field to your model from django_fsm.db.fields import FSMField, transition
class BlogPost(models.Model): state = FSMField(default='new')
transition decorator to annotate model methods
@transition(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. """
source parameter accepts a list of states, or an individual state.
You can use
* for source, to allow switching to
target from any state.
If calling publish() succeeds without raising an exception, the state field will be changed, but not written to the database.
from django_fsm.db.fields 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 Http404; post.publish() post.save() return redirect('/')
If you are using the transition decorator with the
save argument set to
the new state will be written to the database
@transition(source='new', target='published', save=True) def publish(self): """ Side effects other than changing state goes here """
If you require some conditions to be met before changing state, use the
conditions argument to
conditions must be a list of functions
that takes one argument, the model instance. The function must return either
False or a value that evaluates to
False. If all
True, all conditions are considered to be met and transition
is allowed to happen. If one of the functions return
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 True
Or model methods
def can_destroy(self): return self.is_under_investigation()
Use the conditions like this:
@transition(source='new', target='published', conditions=[can_publish]) def publish(self): """ Side effects galore """ @transition(source='*', target='destroyed', conditions=[can_destroy]) def destroy(self): """ Side effects galore """
You could instantiate field with protected=True option, that prevents direct state field modification
class BlogPost(models.Model): state = FSMField(default='new', protected=True) model = BlogPost() model.state = 'invalid' # Raises AttributeError
You could specify FSMField explicitly in transition decorator.
class BlogPost(models.Model): state = FSMField(default='new') @transition(field=state, source='new', target='published') def publish(self): pass
This allows django_fsm to contribute to model class get_available_FIELD_transitions method, that returns list of (target_state, method) available from current model state
Foreign Key constraints support
If you store the states in the db table you could use FSMKeyField to ensure Foreign Key database integrity.
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 procceed
name Transition name
source Source model state
target Target model state
Renders a graphical overview of your models states transitions # 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.Blog
django 1.4.0 2011-12-21 * Add graph_transition command for drawing state transition picture
django-fsm 1.3.0 2011-07-28 * Add direct field modification protection
django-fsm 1.2.0 2011-03-23 * Add pre_transition and post_transition signals
django-fsm 1.1.0 2011-02-22 * Add support for transition conditions * Allow multiple FSMField in one model * Contribute get_available_FIELD_transitions for model class
django-fsm 1.0.0 2010-10-12 * Initial public release