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Django friendly finite state machine support

branch: master
README.md

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 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.

Installation

$ pip install django-fsm

Or, for the latest git version

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

Library has full Python 3 support, for the graph transition drawing you should install python3 compatible graphviz version from git+https://github.com/philipaxer/pygraphviz

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 Http404;

    post.publish()
    post.save()
    return redirect('/')

If some conditions are required to be met before the changing state, use the conditions argument to transition. conditions must be a list of functions that takes 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(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 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

get_available_FIELD_transitions

Returns all transitions data available in current state

get_all_FIELD_transitions

Enumerates all declared transitions

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. This field is also db_index=True by default for speedy db loookups.

class BlogPostStateEnum(object):
    NEW = 10
    PUBLISHED = 20
    HIDDEN = 30

class BlogPostWithIntegerField(models.Model):
    state = FSMIntegerField(default=BlogPostStateEnum.NEW)

    @transition(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

Drawing transitions

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

Changelog

django-fsm

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
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