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Description:

djangofsm2 3.0.0

Django friendly finite state machine support

django-fsm adds simple declarative state management for django models.
Nice introduction is available here: https://gist.github.com/Nagyman/9502133

Django FSM-2 is a fork of Django FSM. Big thanks to Mikhail Podgurskiy for starting and this project and maintaining it for so many years. Unfortunately, development has stalled for almost 2 years and it was officially announced there will be no new releases. Django FSM-2 is the new updated version of Django FSM, with dependencies updates, typing (planed). Original repository: https://github.com/viewflow/django-fsm

Alternatives
If you need parallel task execution, views and background task code reuse
over different flows - check my new project django-viewflow: https://github.com/viewflow/viewflow
Objective
Instead of adding a state field to a django model and managing its
values by hand, you use FSMField and mark model methods with the
transition decorator. These methods could contain side-effects of the
state change.
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.
Installation
$ pip install django-fsm-2

Or, for the latest git version
$ pip install -e git://github.com/pfouque/django-fsm-2.git#egg=django-fsm

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.
"""

The field parameter accepts both a string attribute name or an actual
field instance.
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 can instantiate a field with protected=True option to prevent
direct state field modification.
class BlogPost(models.Model):
state = FSMField(default='new', protected=True)

model = BlogPost()
model.state = 'invalid' # Raises AttributeError

Note that calling
refresh_from_db
on a model instance with a protected FSMField will cause an exception.
source state
source parameter accepts a list of states, or an individual state or
django_fsm.State implementation.
You can use * for source to allow switching to target from any
state.
You can use + for source to allow switching to target from any
state excluding target state.
target state
target state parameter could point to a specific state or
django_fsm.State implementation
from django_fsm import FSMField, transition, RETURN_VALUE, GET_STATE
@transition(field=state,
source='*',
target=RETURN_VALUE('for_moderators', 'published'))
def publish(self, is_public=False):
return 'for_moderators' if is_public else 'published'

@transition(
field=state,
source='for_moderators',
target=GET_STATE(
lambda self, allowed: 'published' if allowed else 'rejected',
states=['published', 'rejected']))
def moderate(self, allowed):
pass

@transition(
field=state,
source='for_moderators',
target=GET_STATE(
lambda self, **kwargs: 'published' if kwargs.get("allowed", True) else 'rejected',
states=['published', 'rejected']))
def moderate(self, allowed=True):
pass

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
If the transition method raises an exception, you can provide a specific
target state
@transition(field=state, source='new', target='published', on_error='failed')
def publish(self):
"""
Some exception could happen here
"""

state_choices
Instead of passing a two-item iterable choices you can instead use the
three-element state_choices, the last element being a string reference
to a model proxy class.
The base class instance would be dynamically changed to the
corresponding Proxy class instance, depending on the state. Even for
queryset results, you will get Proxy class instances, even if the
QuerySet is executed on the 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 instance and user arguments and returns True if the user can
perform the transition.
@transition(field=state, source='*', target='published',
permission=lambda instance, 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):
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 processed
name Transition name
source Source model state
target Target model state
Optimistic locking
django-fsm provides optimistic locking mixin, to avoid concurrent
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 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

Extensions
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 achieved with help of django-fsm-log
package
https://github.com/gizmag/django-fsm-log