django-fsm adds declarative states management for django models.
Instead of adding some state field to a django model, and managing its
values by hand, you could use FSMState field and mark model methods
with the transition decorator. Your method could contain the side-effects
of the state change.
Nice introduction is available here: https://gist.github.com/Nagyman/9502133
You may also take a look at django-fsm-admin project containing a mixin and template tags to integrate django-fsm state transitions into the django admin.
https://github.com/gadventures/django-fsm-admin
Transition logging support could be achived with help of django-fsm-log package
https://github.com/gizmag/django-fsm-log
FSM really helps to structure the code, especially when a new developer comes to the project. FSM is most effective when you use it for some sequential steps.
If you need parallel task execution, view and background task code reuse over different flows - check my new project django-viewflow
https://github.com/kmmbvnr/django-viewflow
$ pip install django-fsmOr, for the latest git version
$ pip install -e git://github.com/kmmbvnr/django-fsm.git#egg=django-fsmThe library has full Python 3 support
Add 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.
"""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 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 could instantiate a 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 AttributeErrorNote that calling refresh_from_db on a model instance with a protected FSMField will cause an exception.
Custom 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
"""In case of transition method would raise exception, you can provide specific target state
@transition(field=state, source='new', target='published', on_error='failed')
def publish(self):
"""
Some exceptio could happends here
"""Instead of passing two elements list choices you could use three elements state_choices,
the last element states for string reference to model proxy class.
Base class instance would be dynamically changed to corresponding Proxy class instance, depending on the state. Even for queryset results, you will get Proxy class instances, even if QuerySet executed on 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 user argument and returns True if user can perform the transition
@transition(field=state, source='*', target='published',
permission=lambda 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 procceed
name Transition name
source Source model state
target Target model state
django-fsm provides optimistic locking mixin, to avoid concurent 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.Blog
- Improved exception message for unmet transition conditions.
- Don't send post transiton signal in case of no state chnages on exception
- Allow empty string as correct state value
- Imporved graphviz fsm visualisation
- Clean django 1.8 warnings
- Support for class substitution to proxy classes depending on the state
- Added ConcurrentTransitionMixin with optimistic locking support
- Default db_index=True for FSMIntegerField removed
- Graph transition code migrated to new graphviz library with python 3 support
- Ability to change state on transition exception
- Support for attaching permission checks on model transitions
- Backward incompatible release
- All public code import moved directly to django_fsm package
- Correct support for several @transitions decorator with different source states and conditions on same method
- save parameter from transition decorator removed
- get_available_FIELD_transitions return Transition data object instead of tuple
- Models got get_available_FIELD_transitions, even if field specified as string reference
- New get_all_FIELD_transitions method contributed to class
- FSMIntegerField and FSMKeyField support
- Ad-hoc support for state fields from proxy and inherited models
- Python 3 compatibility
- Add graph_transition command for drawing state transition picture
- Add direct field modification protection
- Add pre_transition and post_transition signals
- Add support for transition conditions
- Allow multiple FSMField in one model
- Contribute get_available_FIELD_transitions for model class
- Initial public release