Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Django friendly finite state machine support
Python
branch: master

README.md

Django friendly finite state machine support

Build Status Downloads Gitter

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

Installation

$ pip install django-fsm

Or, for the latest git version

$ pip install -e git://github.com/kmmbvnr/django-fsm.git#egg=django-fsm

The library has full Python 3 support

Usage

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 True

Or 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 AttributeError

custom properties

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
    """

on_error state

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
   """

state_choices

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

Permissions

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='publish',
            permission=lambda user: not user.has_perm('myapp.can_make_mistakes'))
def publish(self):
    pass

@transition(field=state, source='*', target='publish',
            permission='myapp.can_remove_post')
def remove(self):
    pass

You 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('/')

Model methods

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

Foreign Key constraints support

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):
        pass

In 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.

Integer Field support

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):
        pass

Signals

django_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

Optimistic locking

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.

Drawing transitions

Renders a graphical overview of your models states transitions

You need pip install graphviz>=0.4 library

# 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

Changelog

django-fsm

django-fsm 2.2.1 2015-04-27

  • 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

django-fsm 2.2.0 2014-09-03

  • 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

django-fsm 2.1.0 2014-05-15

  • Support for attaching permission checks on model transitions

django-fsm 2.0.0 2014-03-15

  • 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

django-fsm 1.6.0 2014-03-15

  • FSMIntegerField and FSMKeyField support

django-fsm 1.5.1 2014-01-04

  • Ad-hoc support for state fields from proxy and inherited models

django-fsm 1.5.0 2013-09-17

  • Python 3 compatibility

django-fsm 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
Something went wrong with that request. Please try again.