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Django friendly finite state machine support.

Project description

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 have full Python 3 support, for 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.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 are using 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 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(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


### get_available_FIELD_transitions

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.

### 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 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

Project details


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