# Django friendly finite state machine support
[](https://github.com/pfouque/django-fsm-2/actions/workflows/test.yml)
[](https://codecov.io/github/pfouque/django-fsm-2)
[](https://github.com/pfouque/django-fsm-2#settings)
[](https://github.com/pfouque/anymail-history/LICENSE)
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
``` bash
$ pip install django-fsm-2
```
Or, for the latest git version
``` bash
$ pip install -e git://github.com/pfouque/django-fsm-2.git#egg=django-fsm
```
## Usage
Add FSMState field to your model
``` python
from django_fsm import FSMField, transition
class BlogPost(models.Model):
state = FSMField(default='new')
```
Use the `transition` decorator to annotate model methods
``` python
@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.
``` python
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
``` python
def can_publish(instance):
# No publishing after 17 hours
if datetime.datetime.now().hour > 17:
return False
return True
```
Or model methods
``` python
def can_destroy(self):
return self.is_under_investigation()
```
Use the conditions like this:
``` python
@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.
``` python
class BlogPost(models.Model):
state = FSMField(default='new', protected=True)
model = BlogPost()
model.state = 'invalid' # Raises AttributeError
```
Note that calling
[refresh_from_db](https://docs.djangoproject.com/en/1.8/ref/models/instances/#django.db.models.Model.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
``` python
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.
``` python
@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
``` python
@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](https://github.com/kmmbvnr/django-fsm/blob/master/tests/testapp/tests/test_state_transitions.py)
for example usage. Or read about [implementation
internals](http://schinckel.net/2013/06/13/django-proxy-model-state-machine/)
### 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.
``` python
@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
``` python
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 :
``` python
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 :
``` 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.
``` python
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()
``` python
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`:
``` python
INSTALLED_APPS = (
...
'django_fsm',
...
)
```
``` bash
# 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>
Raw data
{
"_id": null,
"home_page": "http://github.com/pfouque/django-fsm-2",
"name": "django-fsm-2",
"maintainer": null,
"docs_url": null,
"requires_python": "<4.0,>=3.8",
"maintainer_email": null,
"keywords": null,
"author": "Mikhail Podgurskiy",
"author_email": "kmmbvnr@gmail.com",
"download_url": "https://files.pythonhosted.org/packages/02/78/32a8e14d6c0947c6a41c1c5ecf0e5cf32849a7e6306cadccc52641454c1d/django_fsm_2-3.0.0.tar.gz",
"platform": null,
"description": "# Django friendly finite state machine support\n\n[](https://github.com/pfouque/django-fsm-2/actions/workflows/test.yml)\n[](https://codecov.io/github/pfouque/django-fsm-2)\n[](https://github.com/pfouque/django-fsm-2#settings)\n[](https://github.com/pfouque/anymail-history/LICENSE)\n\n\ndjango-fsm adds simple declarative state management for django models.\n\nNice introduction is available here: <https://gist.github.com/Nagyman/9502133>\n\n> 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>\n\n## Alternatives\n\nIf you need parallel task execution, views and background task code reuse\nover different flows - check my new project django-viewflow: <https://github.com/viewflow/viewflow>\n\n## Objective\n\nInstead of adding a state field to a django model and managing its\nvalues by hand, you use `FSMField` and mark model methods with the\n`transition` decorator. These methods could contain side-effects of the\nstate change.\n\n\nFSM really helps to structure the code, especially when a new developer\ncomes to the project. FSM is most effective when you use it for some\nsequential steps.\n\n## Installation\n\n``` bash\n$ pip install django-fsm-2\n```\n\nOr, for the latest git version\n\n``` bash\n$ pip install -e git://github.com/pfouque/django-fsm-2.git#egg=django-fsm\n```\n\n## Usage\n\nAdd FSMState field to your model\n\n``` python\nfrom django_fsm import FSMField, transition\n\nclass BlogPost(models.Model):\n state = FSMField(default='new')\n```\n\nUse the `transition` decorator to annotate model methods\n\n``` python\n@transition(field=state, source='new', target='published')\ndef publish(self):\n \"\"\"\n This function may contain side-effects,\n like updating caches, notifying users, etc.\n The return value will be discarded.\n \"\"\"\n```\n\nThe `field` parameter accepts both a string attribute name or an actual\nfield instance.\n\nIf calling publish() succeeds without raising an exception, the state\nfield will be changed, but not written to the database.\n\n``` python\nfrom django_fsm import can_proceed\n\ndef publish_view(request, post_id):\n post = get_object_or_404(BlogPost, pk=post_id)\n if not can_proceed(post.publish):\n raise PermissionDenied\n\n post.publish()\n post.save()\n return redirect('/')\n```\n\nIf some conditions are required to be met before changing the state, use\nthe `conditions` argument to `transition`. `conditions` must be a list\nof functions taking one argument, the model instance. The function must\nreturn either `True` or `False` or a value that evaluates to `True` or\n`False`. If all functions return `True`, all conditions are considered\nto be met and the transition is allowed to happen. If one of the\nfunctions returns `False`, the transition will not happen. These\nfunctions should not have any side effects.\n\nYou can use ordinary functions\n\n``` python\ndef can_publish(instance):\n # No publishing after 17 hours\n if datetime.datetime.now().hour > 17:\n return False\n return True\n```\n\nOr model methods\n\n``` python\ndef can_destroy(self):\n return self.is_under_investigation()\n```\n\nUse the conditions like this:\n\n``` python\n@transition(field=state, source='new', target='published', conditions=[can_publish])\ndef publish(self):\n \"\"\"\n Side effects galore\n \"\"\"\n\n@transition(field=state, source='*', target='destroyed', conditions=[can_destroy])\ndef destroy(self):\n \"\"\"\n Side effects galore\n \"\"\"\n```\n\nYou can instantiate a field with `protected=True` option to prevent\ndirect state field modification.\n\n``` python\nclass BlogPost(models.Model):\n state = FSMField(default='new', protected=True)\n\nmodel = BlogPost()\nmodel.state = 'invalid' # Raises AttributeError\n```\n\nNote that calling\n[refresh_from_db](https://docs.djangoproject.com/en/1.8/ref/models/instances/#django.db.models.Model.refresh_from_db)\non a model instance with a protected FSMField will cause an exception.\n\n### `source` state\n\n`source` parameter accepts a list of states, or an individual state or\n`django_fsm.State` implementation.\n\nYou can use `*` for `source` to allow switching to `target` from any\nstate.\n\nYou can use `+` for `source` to allow switching to `target` from any\nstate excluding `target` state.\n\n### `target` state\n\n`target` state parameter could point to a specific state or\n`django_fsm.State` implementation\n\n``` python\nfrom django_fsm import FSMField, transition, RETURN_VALUE, GET_STATE\n@transition(field=state,\n source='*',\n target=RETURN_VALUE('for_moderators', 'published'))\ndef publish(self, is_public=False):\n return 'for_moderators' if is_public else 'published'\n\n@transition(\n field=state,\n source='for_moderators',\n target=GET_STATE(\n lambda self, allowed: 'published' if allowed else 'rejected',\n states=['published', 'rejected']))\ndef moderate(self, allowed):\n pass\n\n@transition(\n field=state,\n source='for_moderators',\n target=GET_STATE(\n lambda self, **kwargs: 'published' if kwargs.get(\"allowed\", True) else 'rejected',\n states=['published', 'rejected']))\ndef moderate(self, allowed=True):\n pass\n```\n\n### `custom` properties\n\nCustom properties can be added by providing a dictionary to the `custom`\nkeyword on the `transition` decorator.\n\n``` python\n@transition(field=state,\n source='*',\n target='onhold',\n custom=dict(verbose='Hold for legal reasons'))\ndef legal_hold(self):\n \"\"\"\n Side effects galore\n \"\"\"\n```\n\n### `on_error` state\n\nIf the transition method raises an exception, you can provide a specific\ntarget state\n\n``` python\n@transition(field=state, source='new', target='published', on_error='failed')\ndef publish(self):\n \"\"\"\n Some exception could happen here\n \"\"\"\n```\n\n### `state_choices`\n\nInstead of passing a two-item iterable `choices` you can instead use the\nthree-element `state_choices`, the last element being a string reference\nto a model proxy class.\n\nThe base class instance would be dynamically changed to the\ncorresponding Proxy class instance, depending on the state. Even for\nqueryset results, you will get Proxy class instances, even if the\nQuerySet is executed on the base class.\n\nCheck the [test\ncase](https://github.com/kmmbvnr/django-fsm/blob/master/tests/testapp/tests/test_state_transitions.py)\nfor example usage. Or read about [implementation\ninternals](http://schinckel.net/2013/06/13/django-proxy-model-state-machine/)\n\n### Permissions\n\nIt is common to have permissions attached to each model transition.\n`django-fsm` handles this with `permission` keyword on the `transition`\ndecorator. `permission` accepts a permission string, or callable that\nexpects `instance` and `user` arguments and returns True if the user can\nperform the transition.\n\n``` python\n@transition(field=state, source='*', target='published',\n permission=lambda instance, user: not user.has_perm('myapp.can_make_mistakes'))\ndef publish(self):\n pass\n\n@transition(field=state, source='*', target='removed',\n permission='myapp.can_remove_post')\ndef remove(self):\n pass\n```\n\nYou can check permission with `has_transition_permission` method\n\n``` python\nfrom django_fsm import has_transition_perm\ndef publish_view(request, post_id):\n post = get_object_or_404(BlogPost, pk=post_id)\n if not has_transition_perm(post.publish, request.user):\n raise PermissionDenied\n\n post.publish()\n post.save()\n return redirect('/')\n```\n\n### Model methods\n\n`get_all_FIELD_transitions` Enumerates all declared transitions\n\n`get_available_FIELD_transitions` Returns all transitions data available\nin current state\n\n`get_available_user_FIELD_transitions` Enumerates all transitions data\navailable in current state for provided user\n\n### Foreign Key constraints support\n\nIf you store the states in the db table you could use FSMKeyField to\nensure Foreign Key database integrity.\n\nIn your model :\n\n``` python\nclass DbState(models.Model):\n id = models.CharField(primary_key=True, max_length=50)\n label = models.CharField(max_length=255)\n\n def __unicode__(self):\n return self.label\n\n\nclass BlogPost(models.Model):\n state = FSMKeyField(DbState, default='new')\n\n @transition(field=state, source='new', target='published')\n def publish(self):\n pass\n```\n\nIn your fixtures/initial_data.json :\n\n``` json\n[\n {\n \"pk\": \"new\",\n \"model\": \"myapp.dbstate\",\n \"fields\": {\n \"label\": \"_NEW_\"\n }\n },\n {\n \"pk\": \"published\",\n \"model\": \"myapp.dbstate\",\n \"fields\": {\n \"label\": \"_PUBLISHED_\"\n }\n }\n]\n```\n\nNote : source and target parameters in \\@transition decorator use pk\nvalues of DBState model as names, even if field \\\"real\\\" name is used,\nwithout \\_id postfix, as field parameter.\n\n### Integer Field support\n\nYou can also use `FSMIntegerField`. This is handy when you want to use\nenum style constants.\n\n``` python\nclass BlogPostStateEnum(object):\n NEW = 10\n PUBLISHED = 20\n HIDDEN = 30\n\nclass BlogPostWithIntegerField(models.Model):\n state = FSMIntegerField(default=BlogPostStateEnum.NEW)\n\n @transition(field=state, source=BlogPostStateEnum.NEW, target=BlogPostStateEnum.PUBLISHED)\n def publish(self):\n pass\n```\n\n### Signals\n\n`django_fsm.signals.pre_transition` and\n`django_fsm.signals.post_transition` are called before and after allowed\ntransition. No signals on invalid transition are called.\n\nArguments sent with these signals:\n\n**sender** The model class.\n\n**instance** The actual instance being processed\n\n**name** Transition name\n\n**source** Source model state\n\n**target** Target model state\n\n## Optimistic locking\n\n`django-fsm` provides optimistic locking mixin, to avoid concurrent\nmodel state changes. If model state was changed in database\n`django_fsm.ConcurrentTransition` exception would be raised on\nmodel.save()\n\n``` python\nfrom django_fsm import FSMField, ConcurrentTransitionMixin\n\nclass BlogPost(ConcurrentTransitionMixin, models.Model):\n state = FSMField(default='new')\n```\n\nFor guaranteed protection against race conditions caused by concurrently\nexecuted transitions, make sure:\n\n- Your transitions do not have any side effects except for changes in\n the database,\n- You always run the save() method on the object within\n `django.db.transaction.atomic()` block.\n\nFollowing these recommendations, you can rely on\nConcurrentTransitionMixin to cause a rollback of all the changes that\nhave been executed in an inconsistent (out of sync) state, thus\npractically negating their effect.\n\n## Drawing transitions\n\nRenders a graphical overview of your models states transitions\n\nYou need `pip install \"graphviz>=0.4\"` library and add `django_fsm` to\nyour `INSTALLED_APPS`:\n\n``` python\nINSTALLED_APPS = (\n ...\n 'django_fsm',\n ...\n)\n```\n\n``` bash\n# Create a dot file\n$ ./manage.py graph_transitions > transitions.dot\n\n# Create a PNG image file only for specific model\n$ ./manage.py graph_transitions -o blog_transitions.png myapp.Blog\n```\n\n## Extensions\n\nYou may also take a look at django-fsm-admin project containing a mixin\nand template tags to integrate django-fsm state transitions into the\ndjango admin.\n\n<https://github.com/gadventures/django-fsm-admin>\n\nTransition logging support could be achieved with help of django-fsm-log\npackage\n\n<https://github.com/gizmag/django-fsm-log>\n",
"bugtrack_url": null,
"license": "MIT",
"summary": "Django friendly finite state machine support.",
"version": "3.0.0",
"project_urls": {
"Documentation": "http://github.com/pfouque/django-fsm-2",
"Homepage": "http://github.com/pfouque/django-fsm-2",
"Repository": "http://github.com/pfouque/django-fsm-2"
},
"split_keywords": [],
"urls": [
{
"comment_text": "",
"digests": {
"blake2b_256": "d0879a29e765cc7c792053798e791706f2b29869733c80eadb22701ea323770e",
"md5": "3b46186cdc814076573734ab2fdb2b19",
"sha256": "5ca98a4c1f5537a54433f3963cd8473dcdc039d9bc8c8045250d290f84a25b35"
},
"downloads": -1,
"filename": "django_fsm_2-3.0.0-py3-none-any.whl",
"has_sig": false,
"md5_digest": "3b46186cdc814076573734ab2fdb2b19",
"packagetype": "bdist_wheel",
"python_version": "py3",
"requires_python": "<4.0,>=3.8",
"size": 21779,
"upload_time": "2024-03-26T10:51:10",
"upload_time_iso_8601": "2024-03-26T10:51:10.241690Z",
"url": "https://files.pythonhosted.org/packages/d0/87/9a29e765cc7c792053798e791706f2b29869733c80eadb22701ea323770e/django_fsm_2-3.0.0-py3-none-any.whl",
"yanked": false,
"yanked_reason": null
},
{
"comment_text": "",
"digests": {
"blake2b_256": "027832a8e14d6c0947c6a41c1c5ecf0e5cf32849a7e6306cadccc52641454c1d",
"md5": "3e795b7f7200671bb40d8a5570047835",
"sha256": "19887dcd6009d9b785f6114527e6542f380c5af7061c47bebefcbad9ace730aa"
},
"downloads": -1,
"filename": "django_fsm_2-3.0.0.tar.gz",
"has_sig": false,
"md5_digest": "3e795b7f7200671bb40d8a5570047835",
"packagetype": "sdist",
"python_version": "source",
"requires_python": "<4.0,>=3.8",
"size": 20299,
"upload_time": "2024-03-26T10:51:12",
"upload_time_iso_8601": "2024-03-26T10:51:12.228040Z",
"url": "https://files.pythonhosted.org/packages/02/78/32a8e14d6c0947c6a41c1c5ecf0e5cf32849a7e6306cadccc52641454c1d/django_fsm_2-3.0.0.tar.gz",
"yanked": false,
"yanked_reason": null
}
],
"upload_time": "2024-03-26 10:51:12",
"github": true,
"gitlab": false,
"bitbucket": false,
"codeberg": false,
"github_user": "pfouque",
"github_project": "django-fsm-2",
"travis_ci": false,
"coveralls": false,
"github_actions": true,
"requirements": [],
"tox": true,
"lcname": "django-fsm-2"
}
JSON
