django-fsm adds declarative states managment 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
with the 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.
$ python setup.py install
Or, for the latest git version
$ pip install -e git://github.com/kmmbvnr/django-fsm.git#egg=django-fsm
Add FSMState field to you model from django_fsm.db.fields import FSMField, transition
class BlogPost(models.Model):
state = FSMField(default='new')
Use the 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 use the transition decorator with the save
argument set to True
,
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 transition
. conditions
must be a list of functions
that take 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 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
"""
If you store the states in the db table you could use FSMKeyField to ensure Foreign Key database integrity.