Viewflow

https://docs.viewflow.io/
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Viewflow is a low-code Django-based platform for building business applications with reusable BPMN...
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### Install Django Viewflow PRO

Source: https://docs.viewflow.io/overview/quick_start.html

Installs the PRO version of Django Viewflow, requiring a license ID for the private index.

```bash
pip install django-viewflow-pro --extra-index-url https://pypi.viewflow.io/<licence_id>/simple/

```

--------------------------------

### Define a Sample Flow with Nodes

Source: https://docs.viewflow.io/workflow/core_concepts.html

This snippet demonstrates how to define a basic Viewflow Flow class with different types of nodes: Start, Handler, If (gateway), and End. It shows how nodes connect using `this` for forward references and includes example methods for performing tasks and checking conditions.

```python
from viewflow import this
from viewflow.workflow import flow, lock, act
from viewflow.workflow.flow import views


class SampleFlow(flow.Flow):
    start = flow.Start(my_view).Next(this.task)

    task = flow.Handler(perform_task).Next(this.check_status)

    check_status = flow.If(this.is_completed).Then(this.end).Else(this.task)

    end = flow.End()

    def perform_task(self, activation):
        activation.process.completed = random.randint(0, 1)

    def is_completed(self, activation):
        return activation.process.completed

```

--------------------------------

### Run Django Migrations and Server

Source: https://docs.viewflow.io/workflow/quick_start.html

Apply database migrations for the 'helloworld' app and start the Django development server to run the workflow.

```bash
./manage.py makemigrations helloworld
./manage.py migrate

./manage.py runserver
```

--------------------------------

### Start Flow Interactively with CreateArtifactView

Source: https://docs.viewflow.io/workflow/writing.html

Use flow.Start with CreateArtifactView to allow users to fill a form to start a flow and create a business object.

```python
from viewflow import this
from viewflow.workflow import flow
from viewflow.workflow.flow import views

class MyFlow(flow.Flow):
    start_with_artifact = (
        flow.Start(views.CreateArtifactView.as_view(model=MyModel, fields=['message']))
        .Annotation(title=_("Fill a form to start flow"))
        .Permission("myapp.can_start_request")
        .Next(this.next_task)
    )


```

--------------------------------

### Base Page Template Example

Source: https://docs.viewflow.io/crud/templates.html

Example of extending the base template for application-specific pages, used for global drawer appearance.

```html
{% extends 'viewflow/base_page.html' %}

TODO: Sample...
```

--------------------------------

### Create Virtual Environment and Activate

Source: https://docs.viewflow.io/overview/quick_start.html

Sets up an isolated Python environment for the project and activates it. Ensure Python 3.8+ and Django 4.0+ are installed.

```bash
python3 -m venv .venv
source .venv/bin/activate

```

--------------------------------

### Install Django Viewflow

Source: https://docs.viewflow.io/overview/quick_start.html

Installs the open-source version of the Django Viewflow package using pip.

```bash
pip install django-viewflow

```

--------------------------------

### Start Flow Programmatically with StartHandle

Source: https://docs.viewflow.io/workflow/writing.html

Use flow.StartHandle to initiate flows from your code, optionally passing initial data.

```python
from viewflow import this
from viewflow.workflow import flow

class MyFlow(flow.Flow):
    start_noninteractive = flow.StartHandle(this.start_process).Next(this.approve)

    def start_process(self, activation, message=''):
        object = MyModel.objects.create(message=message)
        activation.process.artifact = object
        return activation.process

# Start from anywhere in your code
process = MyFlow.start_noninteractive.run(message="Hello World")

```

--------------------------------

### Example FSM in DOT Format

Source: https://docs.viewflow.io/fsm/visualization.html

An example of a document review FSM represented in DOT format, showing states and transitions. This is the raw output format before rendering.

```dot
digraph {
    graph [rankdir=TB, size="8,8"];
    node [shape=box, style="filled", fillcolor="#f5f5f5", fontsize=10];
    edge [fontsize=9];

    NEW [label="NEW", fillcolor="#e1f5fe"];
    UNDER_REVIEW [label="UNDER REVIEW"];
    APPROVED [label="APPROVED"];
    REJECTED [label="REJECTED"];
    PUBLISHED [label="PUBLISHED", fillcolor="#e8f5e9"];

    NEW -> UNDER_REVIEW [label="submit"];
    UNDER_REVIEW -> APPROVED [label="approve"];
    UNDER_REVIEW -> REJECTED [label="reject"];
    APPROVED -> PUBLISHED [label="publish"];
    REJECTED -> NEW [label="revise"];
}

```

--------------------------------

### Main Flow with NSubprocess

Source: https://docs.viewflow.io/workflow/nodes.html

Demonstrates the use of NSubprocess to start multiple instances of a subprocess. Each instance is initiated with a different item from a provided list.

```python
class MainFlowWithNSubprocess(flow.Flow):
    start = flow.StartFunction().Next(this.nsubprocess)
    nsubprocess =
    flow.NSubprocess(ExampleSubFlow.start, lambda p: [1, 2, 3, 4]).Next(this.end)
    end = flow.End()
```

--------------------------------

### Install Dash Dependency

Source: https://docs.viewflow.io/dashboard/index.html

Ensure Dash is installed as a required dependency for creating dashboards. Run this command in your terminal.

```bash
pip install dash

```

--------------------------------

### Example Subprocess Flow

Source: https://docs.viewflow.io/workflow/nodes.html

Defines a simple subprocess flow with start, task, and end points. Used to illustrate subprocess integration.

```python
class ExampleSubFlow(flow.Flow):
    start = flow.StartHandle(this.start_func).Next(this.task)
    task = 
    flow.Handle(this.task_func).Next(this.end)
    end = flow.End()

    def start_func(self, activation, item=0):
        # instantialed with one of 1, 2, 3, 4 as item
        activation.process.data = item

    def task_func(self, activation):
        activation.process.data += 100
```

--------------------------------

### Starting a Flow with a Form

Source: https://docs.viewflow.io/workflow/data_flow.html

Initiate a Viewflow process by specifying a form class for creating the initial process instance.

```python
class SampleFlow(flow.Flow):
    start = flow.Start(
        CreateProcessView.as_view(
            form_class=SelectSourceForm,
        ),
    ).Next(...)
```

--------------------------------

### Basic Site and Application Structure

Source: https://docs.viewflow.io/crud/site.html

Defines a site with applications and viewsets, and sets up URL patterns for authentication and the site itself. This is a foundational setup for organizing your application's structure.

```python
from viewflow.contrib.auth import AuthViewset
from viewflow.urls import Site, Application

site = Site(title="Workforce management", viewsets=[
    Application(
        title='Employees',
        icon=Icon('people'),
        app_name='emp',
        viewsets=[
            EmployeeViewset(),
            DepartmentViewset(),
    ),
])

urlpatterns = [
    path('accounts/', AuthViewset().urls),
    path('', site.urls),
]

```

--------------------------------

### Run Django Development Server

Source: https://docs.viewflow.io/overview/quick_start.html

Starts the Django development server, making the application accessible at http://127.0.0.1:8000.

```bash
./manage.py runserver

```

--------------------------------

### Start Node Configuration

Source: https://docs.viewflow.io/workflow/nodes.html

Defines the initial step of a flow, typically for user interaction. It can be configured with a view, annotations, permissions, and the next node in the sequence.

```python
class MyFlow(flow.Flow):
    start = (
        flow.Start(views.CreateProcessView.as_view(fields=["text"]))
        .Annotation(title=_("New message"))
        .Permission(auto_create=True)
        .Next(this.approve)
    )

    ...
```

--------------------------------

### Custom Process Data Template Example

Source: https://docs.viewflow.io/workflow/templates.html

Example of customizing the process data view by creating a custom template at the flow-specific level.

```django
{# myapp/myapp/process_data.html #}
<div class="process-data-container">
    <h3>Process Information</h3>

    <div class="process-field">
        <label>Process ID:</label>
        <span>{{ process.pk }}</span>
    </div>

    <div class="process-field">
        <label>Started:</label>
        <span>{{ process.created|date:"F j, Y, H:i" }}</span>
    </div>

    <div class="process-field">
        <label>Status:</label>
        <span class="status-badge status-{{ process.status }}">
            {{ process.get_status_display }}
        </span>
    </div>

    {% if process.artifact %}
    <div class="process-field">
        <label>Artifact:</label>
        <a href="{{ process.artifact.get_absolute_url }}">View Details</a>
    </div>
    {% endif %}
</div>


```

--------------------------------

### Start Node Availability

Source: https://docs.viewflow.io/workflow/nodes.html

Specifies which users can initiate a flow. This can be based on username or a callable predicate that returns a boolean.

```python
.Available(username='employee')
.Available(lambda user: user.is_super_user)
```

--------------------------------

### Apply Migrations and Create Superuser

Source: https://docs.viewflow.io/overview/quick_start.html

Applies pending database migrations for installed Django apps and creates an administrator user account.

```bash
./manage.py migrate
./manage.py createsuperuser

```

--------------------------------

### Start a New Django App

Source: https://docs.viewflow.io/crud/quickstart.html

Use the Django startapp command to create a new application. This command initializes the necessary files and structure for a new app within your Django project.

```bash
python manage.py startapp atlas

```

--------------------------------

### Complete Form Definition with Layout and FormSet

Source: https://docs.viewflow.io/forms/layout.html

A comprehensive example demonstrating a Django Form with nested FormSets and a custom layout.

```python
class AddressForm(Form):
    line_1 = forms.CharField(max_length=250)
    line_2 = forms.CharField(max_length=250)
    state = forms.CharField(max_length=100)
    city = forms.CharField(max_length=100)
    zipcode = forms.CharField(max_length=10)

    layout = Layout(
        Caption("Address"),
        "line_1",
        "line_2",
        "state",
        Row("city", "zipcode"),
    )


AddressFormSet = forms.formset_factory(AddressForm, extra=3, can_delete=True)

class SignupForm(Form):
    username = forms.CharField(
        max_length=50,
        widget=forms.TextInput(attrs={"leading-icon": "account_box"}),
    )
    first_name = forms.CharField(max_length=250)
    last_name = forms.CharField(max_length=250)
    date_of_birth = forms.DateField()
    emails = FormSetField(formset_class=EmailFormSet)
    addresses = FormSetField(formset_class=AddressFormSet)

    layout = Layout(
        "username",
        Row("first_name", "last_name", "date_of_birth"),
        "emails",
        FormSet("addresses", card_desktop=4),
    )

```

--------------------------------

### Custom Task Detail Template Example

Source: https://docs.viewflow.io/workflow/templates.html

Example of customizing the task detail view by extending the base template and overriding the 'task_details' block.

```django
{# myapp/myapp/approve_task_detail.html #}
{% extends 'viewflow/workflow/task_detail.html' %}

{% block task_details %}
<div class="custom-task-details">
    <div class="task-header">
        <h3>{{ task.flow_task.task_title }}</h3>
        <span class="task-status status-{{ task.status }}">
            {{ task.get_status_display }}
        </span>
    </div>

    <div class="task-meta">
        <p><strong>Created:</strong> {{ task.created|date:"F j, Y, H:i" }}</p>
        {% if task.owner %}
        <p><strong>Assigned to:</strong>
            {{ task.owner.get_full_name|default:task.owner.username }}
        </p>
        {% endif %}
    </div>

    <div class="task-actions">
        {% if task|can_execute:request.user %}
        <a href="{% url 'myapp:execute_task' process_pk=task.process_id task_pk=task.pk %}"
           class="btn btn-primary">
            Process Task
        </a>
        {% endif %}
    </div>
</div>
{% endblock %}


```

--------------------------------

### Start Node Permissions

Source: https://docs.viewflow.io/workflow/nodes.html

Configures task availability based on user permissions. Permissions can be specified by name or dynamically generated using a callable.

```python
.Permission('my_app.can_approve')
.Permission(lambda process: 'my_app.department_manager_{}'.format(process.department.pk))
```

--------------------------------

### Install Vite as a Dev Dependency

Source: https://docs.viewflow.io/crud/css_and_js.html

Install Vite using npm to manage your JavaScript build process. This is a prerequisite for configuring Vite.

```bash
npm init -y
npm install vite --save-dev
```

--------------------------------

### Custom Transition Action with Permissions and Validation

Source: https://docs.viewflow.io/fsm/rest.html

Implement custom actions for transitions, including permission checks and validation before proceeding. This example shows an 'approve' action.

```python
@action(methods=['POST'], detail=True, url_path='transition/approve')
def approve(self, request, *args, **kwargs):
    instance = self.get_object()
    flow = self.get_object_flow(request, instance)

    if not flow.approve.has_perm(request.user):
        raise PermissionDenied

    if not flow.approve.can_proceed():
        raise ValidationError(_('Transition is not allowed'))

    serializer = self.get_serializer(instance, data=request.data, partial=True)
    serializer.is_valid(raise_exception=True)
    self.perform_update(serializer)

    flow.approve()

    return Response(serializer.data)

```

--------------------------------

### Basic Authentication URL Configuration

Source: https://docs.viewflow.io/contrib/auth.html

Configure URL patterns for user authentication using AuthViewset. This example disables password change functionality.

```python
urlpatterns = [
    path('accounts/', AuthViewset(
        allow_password_change=False,
        login_view=views.LoginView.as_view(
            authentication_form=MyAuthForm
        ),
    ).urls),
]
```

--------------------------------

### Configure URL Routing

Source: https://docs.viewflow.io/workflow/quick_start.html

Add the HelloWorldFlow to your URL configuration using FlowAppViewset to create URLs for starting processes, executing tasks, and viewing details.

```python
from django.urls import path
from viewflow.contrib.auth import AuthViewset
from viewflow.urls import Application, Site, ModelViewset
from viewflow.workflow.flow import FlowAppViewset
from helloworld.flows import HelloWorldFlow


site = Site(title="ACME Corp", viewsets=[
    Application(
        title='Sample App', icon='people', app_name='sample', viewsets=[
            FlowAppViewset(HelloWorldFlow, icon="assignment"),
        ]
    ),
])

urlpatterns = [
    path('accounts/', AuthViewset(with_profile_view=False).urls),
    path('', site.urls),
]
```

--------------------------------

### Django Admin Integration Setup

Source: https://docs.viewflow.io/contrib/admin.html

Set up the Django administration Viewset adapter for quick access to Django admin from your main website. This requires importing necessary modules and configuring the site URLs.

```python
from django.contrib import admin
from viewflow.contrib.admin import Admin

site = Site(viewsets=[
    Admin()
])

urls = [
    path("admin/", admin.site.urls),
    path('', site.urls)
]

```

--------------------------------

### Start multiple instances of a subprocess flow

Source: https://docs.viewflow.io/workflow/nodes.html

Use NSubprocess node to start multiple instances of a subprocess flow, each processing a different item. All subprocesses must complete before the parent flow proceeds. This feature is available in PRO versions.

```python
class ExampleSubFlow(flow.Flow):
    start = flow.StartHandle(this.start_func).Next(this.task) task = 
    flow.Handle(this.task_func).Next(this.end)
    end = flow.End()

    def start_func(self, activation, item=0):
        # instantialed with one of 1, 2, 3, 4 as item
        activation.process.data = item

    def task_func(self, activation):
        activation.process.data += 100

class MainFlowWithNSubprocess(flow.Flow):
    start = flow.StartFunction().Next(this.nsubprocess) nsubprocess =
    flow.NSubprocess(ExampleSubFlow.start, lambda p: [1, 2, 3, 4]).Next(this.end)
    end = flow.End()

```

--------------------------------

### Timer Node Usage

Source: https://docs.viewflow.io/workflow/nodes.html

Example of using the Timer node to introduce a delay before proceeding to the next step in a workflow. Requires importing the celery module.

```python
from viewflow.contrib import celery

class MyFlow(Flow):
    ...
    wait = celery.Timer(timedelta(minutes=10)).Next(this.check)
    ...._
```

--------------------------------

### Execute OnCreate Task Event

Source: https://docs.viewflow.io/workflow/nodes.html

Defines a callback function to be executed when a task is created. This example shows how to send an email notification when a task is assigned.

```python
class MyFlow(Flow):
    approve = flow.View(...).OnCreate(this.on_approve_created)

    def on_approve_created(self, activation):
        if activation.task.owner:
            send_mail(
                'View task assigned to you','Here is the message.',
                'from@example.com', [activation.task.owner.email]
            )
```

--------------------------------

### Define HelloWorldFlow

Source: https://docs.viewflow.io/workflow/quick_start.html

Map the BPMN diagram to Python code by defining nodes like start, approve, check_approve, send, and end using viewflow.workflow.flow classes.

```python
from viewflow import this
from viewflow.workflow import flow, lock, act
from viewflow.workflow.flow import views

from .models import HelloWorldProcess


class HelloWorldFlow(flow.Flow):
    process_class = HelloWorldProcess

    start = (
        flow.Start(views.CreateProcessView.as_view(fields=["text"]))
        .Annotation(title="New message")
        .Permission(auto_create=True)
        .Next(this.approve)
    )

    approve = (
        flow.View(views.UpdateProcessView.as_view(fields=["approved"]))
        .Permission(auto_create=True)
        .Next(this.check_approve)
    )

    check_approve = (
        flow.If(act.process.approved)
        .Then(this.send)
        .Else(this.end)
    )

    send = (
        flow.Function(this.send_hello_world_request)
        .Next(this.end)
    )

    end = flow.End()

    def send_hello_world_request(self, activation):
        print(activation.process.text)
```

--------------------------------

### Custom Transition Action

Source: https://docs.viewflow.io/fsm/rest.html

Provides an example of a custom transition action method (`approve`) within a ViewSet. This method handles permission checks, transition validation, object updates, and the actual flow transition execution.

```APIDOC
## Custom Transition Action: approve

### Description
Handles the 'approve' transition action, including permission checks, validation, and execution.

### Method
POST

### Endpoint
`/your-endpoint/transition/approve`

### Parameters
#### Path Parameters
- **id** (int) - Required - The ID of the object to approve.

#### Query Parameters
None explicitly defined.

#### Request Body
- **(fields depend on serializer_class)** - Optional - Data for partial update.

### Request Example
```json
{
  "example": "request body"
}
```

### Response
#### Success Response (200)
- **(fields depend on serializer_class)** - Description of the updated object after approval.

#### Response Example
```json
{
  "example": "response body"
}
```
```

--------------------------------

### Customize Create and Update Forms

Source: https://docs.viewflow.io/crud/crud.html

Customize form layouts, classes, and widgets for create and update operations. This example shows setting a specific update form class and defining form widgets with dependent selections.

```python
class ContinentViewset(ModelViewset):
    # ... other options ...

    create_form_layout = Layout(
        # Layout configuration for create form
    )

    form_layout = Layout(
        # Layout configuration
    )

    update_form_class = forms.ContinentForm

    form_widgets = {
        'planet': DependentModelSelect(
            depends_on='galaxy',
            queryset=lambda galaxy: Planet.objects.filter(galaxy=galaxy)
        )
    }
```

--------------------------------

### Subprocess Node for Nested Workflows (PRO-only)

Source: https://docs.viewflow.io/workflow/nodes.html

The Subprocess node starts a nested workflow. The parent flow pauses until the subprocess is completed. This example shows how to define a main flow that includes a subprocess.

```python
class ExampleSubFlow(flow.Flow):
    start = flow.StartHandle(this.start_func).Next(this.task)
    task = flow.Handle(this.task_func).Next(this.end)
    end = flow.End()

    def start_func(self, activation):
        # get access to parent process and data
        activation.process.parent_task.process.data

    def task_func(self, activation):
        pass

class MainFlowWithSubprocess(flow.Flow):
    start = flow.StartHandle().Next(this.subprocess)
```

--------------------------------

### Create Django Project and App

Source: https://docs.viewflow.io/overview/quick_start.html

Generates the basic structure for a Django project named 'demo' and an app named 'helloworld'.

```bash
django-admin startproject demo .
./manage.py startapp helloworld

```

--------------------------------

### Create Vite Project Structure

Source: https://docs.viewflow.io/crud/css_and_js.html

Prepare your project directory by creating the 'components' folder and an empty 'index.js' file within it. This structure is required by the Vite configuration.

```bash
mkdir components/
touch components/index.js
```

--------------------------------

### Defining a Basic Viewset

Source: https://docs.viewflow.io/crud/viewset.html

Demonstrates how to create a custom Viewset by inheriting from `viewflow.urls.Viewset` and defining URL paths as class attributes.

```python
from django.urls import path
from viewflow.urls import Viewset

class WebsiteViewset(Viewset):
    index_path = path('', index_view, name='index')

```

--------------------------------

### Inherit from ModelViewset

Source: https://docs.viewflow.io/crud/crud.html

Inherit from a viewset class to override methods and attributes for custom behavior. This example defines a DepartmentViewset.

```python
class DepartmentViewset(ModelViewset):
    icon = Icon('people')
    model = models.Department
    list_columns = ('name', 'manager', 'parent')
    list_filter_fields = ('parent', )
```

--------------------------------

### Configure Django Settings for Viewflow

Source: https://docs.viewflow.io/overview/quick_start.html

Adds 'viewflow' and the custom app 'helloworld' to the INSTALLED_APPS list in the Django project's settings.

```python
INSTALLED_APPS = [
    ...
    'viewflow',
    'helloworld',
]

```

--------------------------------

### Defining a URL Path as a Property

Source: https://docs.viewflow.io/crud/viewset.html

Illustrates how to define a URL path dynamically using a property, allowing for more complex logic or dynamic path generation.

```python
@property
def page_path(self):
    return path('page/', self.page_view, name='page'))

def page_view(self, request):
    return render(request, 'page.html')

```

--------------------------------

### reverse

Source: https://docs.viewflow.io/workflow/viewsets.html

Get the URL for a given viewname, including the namespace. This function is useful for dynamically generating URLs within your application.

```APIDOC
## reverse

### Description
Get the URL for a given viewname, including the namespace.

### Method
N/A (Python function)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Keyword Arguments
- **viewname** (str) - Required - The name of the view.
- **args** (Optional[List[Any]]) - Optional - Positional arguments for the view.
- **kwargs** (Optional[Dict[str, Any]]) - Optional - Keyword arguments for the view.
- **current_app** (Optional[str]) - Optional - The current application namespace.

### Returns
- **str** - The URL for the view with the appropriate namespace
```

--------------------------------

### Task Permissions with Auto Creation

Source: https://docs.viewflow.io/workflow/nodes.html

Demonstrates how to define task-specific permissions that can be automatically created during migrations. This includes specifying codenames and help text.

```python
# Creates `process_class.can_do_task_process_class` permission
do_task = View().Permission(auto_create=True)

# You can specify permission codename and description right here
# The following creates `process_class.can_execute_task` permission
do_task = View().Permission('can_execute_task', help_text='Custom text', auto_create=True)
```

--------------------------------

### Restricting Site/Application Access

Source: https://docs.viewflow.io/crud/site.html

Implements a `has_perm` method to control access to a site or application. This example restricts access to users who are staff members.

```python
def has_perm(request, user):
    return user.is_staff


```

--------------------------------

### Layout with Column and Responsive Sizing

Source: https://docs.viewflow.io/forms/layout.html

Illustrates using Column to stack elements vertically and Span within a Row to control responsive sizing for different devices.

```python
layout = Layout(
     Row(
         Column('first_name', 'last_name', desktop=8, tablet=6),
         'sex_options'
     )
 )

```

--------------------------------

### Handle State Transitions in Django Views

Source: https://docs.viewflow.io/fsm/models.html

Implement Django views to handle FSM transitions, including permission checks and form processing.

```python
from django.shortcuts import get_object_or_404, redirect, render
from django.core.exceptions import PermissionDenied
from .models import Report
from .forms import ApproveForm
from .flow import ReportFlow

def approve(request, report_pk):
    report = get_object_or_404(Report, pk=report_pk)
    flow = ReportFlow(report)

    if not flow.approve.has_perm(request.user):
        raise PermissionDenied

    form = ApproveForm(request.POST or None, instance=report)
    if form.is_valid():
        form.save(commit=False)
        flow.approve()
        return redirect('../')

    return render(request, 'approve.html', {
        'report': report,
        'flow': flow,
        'form': form
    })

```

--------------------------------

### Define a Django Model

Source: https://docs.viewflow.io/crud/quickstart.html

Define a new model in your app's models.py file. This example creates a 'City' model with 'name' and 'population' fields.

```python
from django.db import models

class City(models.Model):
    name = models.CharField(max_length=250)
    population = models.PositiveIntegerField()

```

--------------------------------

### StartHandle Node Initialization

Source: https://docs.viewflow.io/workflow/nodes.html

Initializes a flow from code using a StartHandle node, which is linked to a callable function for process initiation. It also defines the next node and allows passing arguments.

```python
class MyFlow(flow.Flow):
    start = flow.StartHandle(this.on_start_process).Next(this.approve)

    def start_process(self, activation, sample=False):
        activation.process.sample = sample
        return activation.process

    ...

process = MyFlow.start.run(sample=True)
```

--------------------------------

### Include Single Flow into URL Patterns

Source: https://docs.viewflow.io/workflow/viewsets.html

Use FlowViewset to include a single flow into your Django URL patterns. This is a basic setup for a standalone flow.

```python
urlpatterns = [
    path("my_flow/", FlowViewset(MyFlow).urls)
]
```

--------------------------------

### Render Chart as PNG in Django View

Source: https://docs.viewflow.io/fsm/visualization.html

Converts the DOT graph to PNG format using pydot and returns it as an HTTP response. Ensure pydot is installed and configured.

```python
import pydot
from django.http import HttpResponse
from viewflow.fsm import chart
from .flow import ReportFlow

def flow_chart_image(request):
    dot_graph = chart(ReportFlow.state_field)

    graphs = pydot.graph_from_dot_data(dot_graph)
    graph = graphs[0]
    png_data = graph.create_png()

    return HttpResponse(png_data, content_type='image/png')

```

--------------------------------

### Set Up Django URLs with Viewflow Site and Auth

Source: https://docs.viewflow.io/overview/quick_start.html

Configures the main URL patterns for the Django project, integrating Viewflow's Site for application management and AuthViewset for authentication.

```python
from django.urls import path
from django.contrib.auth.models import User
from viewflow.contrib.auth import AuthViewset
from viewflow.urls import Application, Site, ModelViewset


site = Site(title="ACME Corp", viewsets=[
    Application(
        title='Sample App',
        icon='people',
        app_name='sample',
        viewsets=[
            ModelViewset(model=User),
        ]
    ),
])

urlpatterns = [
    path('accounts/', AuthViewset(with_profile_view=False).urls),
    path('', site.urls),
]

```

--------------------------------

### Customize Queryset with select_related

Source: https://docs.viewflow.io/crud/crud.html

Customize the queryset for a viewset to optimize querying or restrict listed models. This example uses select_related for performance and overrides get_queryset for user-specific filtering.

```python
class EmployeeViewset(DetailViewMixin, ModelViewset):
    model = models.Employee
    queryset = model._default_manager.select_related('department')

    def get_queryset(self, request):
         if not request.user.is_staff:
              return self.queryset.exclude(department__parent_isnull=True)
         return self.queryset
```

--------------------------------

### Defining Editable Fields for Transitions

Source: https://docs.viewflow.io/fsm/admin.html

Specify which fields should be editable alongside transitions by overriding the get_transition_fields method. This example allows editing 'text' and 'comment' for the 'approve' transition.

```python
def get_transition_fields(self, request, obj, slug):
    if slug == 'approve':
        return ['text', 'comment']


```

--------------------------------

### Embedding a Formset for Many-to-Many with InlineFormSetField and AjaxModelSelect

Source: https://docs.viewflow.io/forms/formsets.html

Configure InlineFormSetField for many-to-many relationships using a 'through' model. The example demonstrates using AjaxModelSelect for efficient, on-demand loading of related choices.

```python
from django.contrib.auth.models import User, Group
from django.forms.models import inlineformset_factory
from viewflow.forms import ModelForm, InlineFormSetField, AjaxModelSelect


GroupFormSet = inlineformset_factory(
    User,
    Group.user_set.through,
    fields=("group",),
    can_delete=False,
    extra=1,
    widgets={"group": AjaxModelSelect(lookups=["name__istartswith"])}
)


class UserForm(ModelForm):
    groups = InlineFormSetField(formset_class=GroupFormSet)

    class Meta:
        model = User
        fields = ["username", "first_name", "last_name"]

```

--------------------------------

### This Shortcut

Source: https://docs.viewflow.io/workflow/api.html

Helper for building forward references to class attributes and methods, allowing references before declaration.

```APIDOC
## Class This

### Description
Helper for building forward references to class attributes and methods.

### Methods
- **resolve(instance: object, this_ref: ThisObject | ThisMethod | Any)**: Resolve a forward reference on the given instance.
    Args:
        instance (object): The instance on which to resolve the reference.
        this_ref (Union[ThisObject, ThisMethod, Any]): The reference to resolve.
    Returns:
        Any: The resolved reference.
    Raises:
        AttributeError: If the reference cannot be resolved.
```

--------------------------------

### Create Custom Permission with Codename and Description

Source: https://docs.viewflow.io/workflow/nodes.html

Allows specifying a custom codename and help text for a permission, providing more descriptive access control. The permission created is `process_class.can_execute_task`.

```python
do_task = View().Permission('can_execute_task', help_text='Custom text', auto_create=True)
```

--------------------------------

### Start a subprocess flow within a parent flow

Source: https://docs.viewflow.io/workflow/nodes.html

Use Subprocess node to initiate a subprocess flow. The parent flow pauses until the subprocess is completed. This feature is available in PRO versions.

```python
class ExampleSubFlow(flow.Flow):
    start = flow.StartHandle(this.start_func).Next(this.task)
    task = flow.Handle(this.task_func).Next(this.end)
    end = flow.End()

    def start_func(self, activation):
        # get access to parent process and data
        activation.process.parent_task.process.data

    def task_func(self, activation):
        pass

class MainFlowWithSubprocess(flow.Flow):
    start = flow.StartHandle().Next(this.subprocess)
    subprocess = flow.Subprocess(ExampleSubFlow.start).Next(this.end)
    end = flow.End()

```

--------------------------------

### Nesting Viewsets

Source: https://docs.viewflow.io/crud/viewset.html

Explains how to nest one Viewset within another using the `route` function to create hierarchical URL structures.

```python
from viewflow.urls import route, Viewset

class UserViewset(Viewset):
    page_path = path('account/', self.account_view name="account")

class WebsiteViewset(Viewset):
    users_path = route('auth/', UserViewset())

```

--------------------------------

### Define CompositeKey in Django Model

Source: https://docs.viewflow.io/orm/composite_fk.html

Example of defining a CompositeKey field in a Django model to access a database table with a composite foreign key. This field is virtual and intended for models where Meta.managed = False.

```python
from viewflow.fields import CompositeKey

class Seat(models.Model):
    id = CompositeKey(columns=['aircraft_code', 'seat_no'])
    aircraft_code = models.ForeignKey(Aircraft, models.DO_NOTHING)
    seat_no = models.CharField(max_length=4)

class Meta:
    managed = False
    db_table = 'aircrafts_data'
```

--------------------------------

### Context Variables for Process Detail Template

Source: https://docs.viewflow.io/workflow/templates.html

Provides context variables available within the process detail template.

```python
{
    'process': Process model instance,
    'flow_class': The Flow class,
    'tasks': QuerySet of Task instances
}

```

--------------------------------

### Custom Navigation Menu HTML

Source: https://docs.viewflow.io/crud/site.html

An example of a custom HTML template for an application's navigation menu. It uses Viewflow's template tags to render menu items for employees and departments.

```html
{% load viewflow_site %}
<vf-page-menu-navigation class="mdc-list">
<div class="mdc-list-group">
    <h3 class="vf-page__menu-subheader mdc-list-group__subheader">Employees</h3>
    <a class="mdc-list-item vf-page__menu-list-item"
       href="{% url 'emp:employee:index' %}">
    <i class="material-icons">account_box</i>Employees
    </a>
    <a class="mdc-list-item vf-page__menu-list-item"
       href="{% url 'emp:department:index' %}">
        <i class="material-icons">people</i>Departments
    </a>
</div>
<div class="mdc-list-divider"></div>
</vf-page-menu-navigation>


```

--------------------------------

### Reversing URLs with Namespaces

Source: https://docs.viewflow.io/crud/viewset.html

Demonstrates how to use Django's `reverse` function to generate URLs for views defined within Viewsets, considering default and nested namespaces.

```python
from django.urls import reverse

>>> reverse('website:index')
'/'

>>> reverse('website:page')
'/page/'

>>> reverse('website:user:account')
'/auth/account/'

```

--------------------------------

### Initializing Task Data Conditionally

Source: https://docs.viewflow.io/workflow/data_flow.html

Create a task with pre-initialized data based on a condition, using lambda functions to define the data.

```python
# Create task with preinitialized data
next_task = (
    flow.If(
        cond=lambda activation: activation.task.seed.fresh
    )
    .Then(
        this.plant,
        task_data=lambda activation: {'seed': activation.task.seed}
    )
    .Else(
        this.eat,
        task_data=lambda activation: {'grain': activation.task.seed}
    )
)
```

--------------------------------

### Define FSM States and Transitions

Source: https://docs.viewflow.io/fsm/index.html

Demonstrates how to define states using an Enum and transitions using the @transition decorator. States cannot be assigned directly and must be changed via defined transitions.

```python
from enum import Enum
from viewflow.fsm import State

class States(Enum):
   NEW = 1
   DONE = 2
   HIDDEN = 3


class MyFlow(object):
   state_field = State(States, default=States.NEW)

   @state_field.transition(source=States.NEW, target=States.DONE)
   def complete():
       pass

   @state_field.transition(source=State.ANY, target=States.HIDDEN)
   def hide():
       pass

flow = MyFlow()
flow.state_field == States.NEW  # True
flow.state_field = States.DONE  # Raises AttributeError

flow.complete()
flow.state_field == States.DONE  # True

flow.complete()  # Raises TransitionNotAllowed

```

--------------------------------

### Enable Pessimistic Locking in Flow

Source: https://docs.viewflow.io/workflow/core_concepts.html

To enable pessimistic locking in Viewflow, specify the `lock_impl` attribute in your Flow class. This example uses `lock.select_for_update_lock` to acquire a database lock during view execution, preventing race conditions.

```python
from viewflow.workflow import lock

class SampleFlow(flow.Flow):
    lock_impl = lock.select_for_update_lock

```

--------------------------------

### Site Branding with Colors

Source: https://docs.viewflow.io/crud/site.html

Sets primary and secondary colors for site branding. This allows for quick customization of the site's visual theme.

```python
site = Site(
    title="Workforce management",
    primary_color='#3949ab',
    secondary_color='#5c6bc0',
    viewsets=[
        EmployeeViewset(),
        DepartmentViewset(),
    ]
)


```

--------------------------------

### Overriding a Custom Transition View

Source: https://docs.viewflow.io/fsm/admin.html

Completely replace a transition's view by defining custom URLs and view logic. This example shows how to override the 'reject' transition view, including permission checks and state updates.

```python
def get_urls(self):
    return [path(
        '<path:object_id>/transition/reject/',
        self.admin_site.admin_view(self.reject_view),
    )] + super().get_urls()

def reject_view(self, request, object_id):
    obj = get_object_or_404(self.model, pk=object_id)
    flow = self.get_object_flow(request, obj)

    if not flow.reject.has_perm(request.user) or not flow.reject.can_proceed():
        raise PermissionDenied

    if request.method == "POST":
        flow.reject()
        obj.save()
        return redirect('../../')

    return render(request, ...)


```

--------------------------------

### Send Hello World Request Task

Source: https://docs.viewflow.io/workflow/writing.html

A Celery task to demonstrate background processing within a Viewflow activation. It updates a process field without using locks.

```python
from celery import shared_task
from viewflow.flow import flow_job


@shared_task
def send_hello_world_request(activation_ref):
    with Job.activate(activation_ref) as activation:
        result = 'Background Processing Done'

        # No locks during long jobs - save carefully
        activation.process.sample_text = result
        activation.process.save(updated_fields=['sample_text'])
```

--------------------------------

### AJAX Autocomplete Request Handling

Source: https://docs.viewflow.io/forms/widgets.html

Illustrates how to handle an AJAX OPTIONS request for autocomplete suggestions, extracting query parameters.

```python
if request.method == "OPTIONS" and "HTTP_X_REQUEST_AUTOCOMPLETE" in request.META:
    query = request.META.get("HTTP_X_REQUEST_AUTOCOMPLETE")
    options = QueryDict(query, encoding=self.request.encoding)
    field_name = options.get("field", "")
    query = options.get("query")
    ...

```

--------------------------------

### Link Business Data using Generic Foreign Key

Source: https://docs.viewflow.io/workflow/writing.html

Store business data in separate models and link to them using the Process model's 'artifact' generic foreign key.

```python
class MyModel(models.Model):
    message = models.CharField(max_length=150)


 def task_view(request, **kwargs):
     form = MyModelForm(request.POST or None)

     if form.is_valid():
         object = form.save(commit=True)
         request.activation.process.artifact = object

     # additional code here..

```

--------------------------------

### Basic FSM Viewset Integration

Source: https://docs.viewflow.io/fsm/viewset.html

Integrates a Django model with a Flow class using FlowViewsMixin and ModelViewSet. Exposes transitions as detail actions.

```Python
# viewset.py

from viewflow.fsm import FlowViewsMixin
from viewflow.views import ModelViewSet
from .flow import ReportFlow
from .models import Report

class ReportViewSet(FlowViewsMixin, ModelViewSet):
    model = Report
    flow_class = ReportFlow

    queryset = Report.objects.all()
    list_display = ['id', 'text', 'state_field']
    detail_actions = ['approve', 'reject', 'publish']

```

--------------------------------

### Initializing Branches with Specific Data

Source: https://docs.viewflow.io/workflow/data_flow.html

When splitting work, initialize each branch task with its own data, often derived from process data.

```python
split = (
    flow.Split()
    .Next(
        this.process_post,
        task_data_source=lambda activation: {'post': post} for post in activation.process.data['posts'],
    )
    .Next(this.join)
)
```

--------------------------------

### Define Polymorphic User and Client Models

Source: https://docs.viewflow.io/orm/json_storage.html

Demonstrates polymorphic model inheritance using JSON Store. A base User model with a JSONField is extended by Client proxy models, allowing different real-life objects without multi-table inheritance.

```python
from django.contrib.auth.models import AbstractUser
from viewflow import jsonstore

class User(PolymorphicModel, AbstractUser):
    data = jsonstore.JSONField(null=True, default=dict)

class Client(User):
    address = jsonstore.CharField(max_length=250)
    zip_code = jsonstore.CharField(max_length=250)
    city = jsonstore.CharField(max_length=250)
    vip = jsonstore.BooleanField()

    class Meta:
        proxy = True
```

--------------------------------

### Custom Transition Form for FSM Viewset

Source: https://docs.viewflow.io/fsm/viewset.html

Defines a custom form for a specific transition and overrides the viewset to use it. Handles form data during transition.

```Python
# forms.py

from django import forms
from .models import Report

class ApproveForm(forms.ModelForm):
    comment = forms.CharField(widget=forms.Textarea)

    class Meta:
        model = Report
        fields = []

```

```Python
# viewset.py

class ReportViewSet(FlowViewsMixin, ModelViewSet):
    # ...previous configuration...

    def get_transition_form_class(self, transition_name):
        if transition_name == 'approve':
            return ApproveForm
        return super().get_transition_form_class(transition_name)

    def perform_transition(self, instance, transition_name, form=None):
        flow = self.get_flow_instance(instance)
        if transition_name == 'approve' and form is not None:
            instance.approval_comment = form.cleaned_data['comment']

        transition = getattr(flow, transition_name)
        transition()

```

--------------------------------

### Viewflow Template Tags and Filters Usage

Source: https://docs.viewflow.io/workflow/templates.html

Demonstrates how to use Viewflow's template tags for generating task and process action URLs, displaying flow diagrams, and checking user permissions.

```django
{% load viewflow workflow %}

{# Task action URLs #}
<a href="{% task_action_url task 'assign' %}">Assign</a>
<a href="{% task_action_url task 'execute' %}">Execute</a>
<a href="{% task_action_url task 'unassign' %}">Unassign</a>

{# Process action URLs #} 
<a href="{% process_action_url process 'cancel' %}">Cancel Process</a>
<a href="{% process_action_url process 'detail' %}">View Details</a>

{# Flow diagram #}
{% flow_diagram flow_class task=task %}

{# Permission checks #}
{% if task|can_execute:request.user %}
    <button type="button">Execute Task</button>
{% endif %}

{% if task|can_assign:request.user %}
    <button type="button">Assign Task</button>
{% endif %}
```

--------------------------------

### Act Shortcut

Source: https://docs.viewflow.io/workflow/api.html

Shortcut to access activation data, providing access to the current process and task within an activation context.

```APIDOC
## Class Act

### Description
Shortcut to access activation data.

### Properties
- **process** (property): Shortcut for lambda activation: activation.process…
- **task** (property): Shortcut for lambda activation: activation.task…
```

--------------------------------

### FSM State Visualization URL Configuration

Source: https://docs.viewflow.io/fsm/viewset.html

Configures Django URLs to include the state machine chart generated by the FSM Viewset.

```Python
# urls.py

from django.urls import path, include
from .viewset import ReportViewSet

urlpatterns = [
    path('reports/', include(ReportViewSet().urls)),
    # Creates /reports/chart/ for the FSM diagram
]

```

--------------------------------

### Context Variables for Process List Template

Source: https://docs.viewflow.io/workflow/templates.html

Provides context variables available within the process list template.

```python
{
    'flow_class': The Flow class,
    'process_list': QuerySet of Process instances,
    'filter_form': Process filter form (if enabled)
}

```

--------------------------------

### Parallel Execution with flow.Split and flow.Join

Source: https://docs.viewflow.io/workflow/writing.html

Implements parallel task execution using flow.Split to create branches and flow.Join to synchronize their completion before proceeding.

```python
from viewflow import this
from viewflow.workflow import flow

class MyFlow(flow.Flow):
    process_class = MyProcess

    start = (
        flow.Start(...)
        .Next(this.parallel_tasks)
    )

    parallel_tasks = (
        flow.Split()
        .Next(this.task1).Next(this.task2)
    )

    task1 = flow.View(...)
        .Next(this.join)

    task2 = flow.View(...)
        .Next(this.join)

    join = flow.Join()
        .Next(this.next_step)

    next_step = flow.End()
```

--------------------------------

### Render a Viewflow Form in a Template

Source: https://docs.viewflow.io/forms/quick_start.html

Use the `{% load viewflow %}` template tag and the `{% render form form.layout %}` tag to display the form. Wrap the form in `<vf-form/>` to enable AJAX submission.

```html
{% load viewflow %}
<vf-form>
    <form class="vf-form" method="POST" enctype="multipart/form-data">
        {% csrf_token %}
        <section class="vf-card__form">
            {% render form form.layout %}
        </section>
        <section class="mdc-card__actions vf-card__actions">
            <button class="mdc-button mdc-card__action mdc-card__action--button mdc-button--raised" type="submit">
                {% trans "Save" %}
            </button>
        </section>
    </form>
</vf-form>

```

--------------------------------

### Passing Data to Subprocesses

Source: https://docs.viewflow.io/workflow/data_flow.html

Initialize subprocesses with specific seed and data, such as passing the parent process artifact as the subprocess seed.

```python
publish_post = flow.Subprocess(
    PublishFlow.as_subprocess,
    process_seed=lambda activation: activation.process.artifact,
).Next(this.end)
```

--------------------------------

### Custom Serializer Per Transition

Source: https://docs.viewflow.io/fsm/rest.html

Illustrates how to define custom serializer classes for specific transitions within a ViewSet. This allows for different data serialization logic based on the transition action.

```APIDOC
## Custom Serializer Per Transition

### Description
Allows specifying a custom serializer class for specific transition actions.

### Method
POST

### Endpoint
`/your-endpoint/` (inferred from ModelViewSet)

### Parameters
#### Path Parameters
- **id** (int) - Required - The ID of the object.

#### Query Parameters
None explicitly defined.

#### Request Body
- **(fields depend on serializer_class)** - Optional - Data for partial update.

### Request Example
```json
{
  "example": "request body"
}
```

### Response
#### Success Response (200)
- **(fields depend on serializer_class)** - Description of the updated object.

#### Response Example
```json
{
  "example": "response body"
}
```
```

--------------------------------

### Define HelloWorldProcess Model

Source: https://docs.viewflow.io/workflow/quick_start.html

Define the process model inheriting from viewflow.workflow.models.Process, adding custom fields like 'text' and 'approved'.

```python
from django.db import models
from viewflow import jsonstore
from viewflow.workflow.models import Process


class HelloWorldProcess(Process):
    text = jsonstore.CharField(max_length=150)
    approved = jsonstore.BooleanField(default=False)

    class Meta:
        proxy = True
```

--------------------------------

### Custom Process Model with Direct Inheritance

Source: https://docs.viewflow.io/workflow/data_flow.html

Inherit directly from the Process model to add custom fields and database columns.

```python
class ShipmentProcess(Process):
    carrier = models.ForeignKey(Carrier, on_delete=models.CASCADE)
```

--------------------------------

### Configure Vite for Library Build

Source: https://docs.viewflow.io/crud/css_and_js.html

Set up vite.config.js to build your JavaScript components as an IIFE library. This configuration specifies source maps, output directory, and library details.

```javascript
import { defineConfig } from 'vite'

export default defineConfig({
    build: {
        sourcemap: true,
        emptyOutDir: false,
        outDir: 'static/js/',
        lib: {
        entry: 'components/index.js',
        formats: ['iife'],
        name: 'my_components',
        fileName: () => "my_components.min.js",
        },
    }
})
```

--------------------------------

### Process Model

Source: https://docs.viewflow.io/workflow/api.html

Default viewflow Process model, inheriting from AbstractProcess. Includes exceptions for DoesNotExist and MultipleObjectsReturned.

```APIDOC
## Class Process

### Description
Default viewflow Process model.

### Exceptions
- **DoesNotExist**
- **MultipleObjectsReturned**
```

--------------------------------

### Including Viewset URLs in Root URL Configuration

Source: https://docs.viewflow.io/crud/viewset.html

Shows how to integrate a Viewset's URLs into your main Django `urls.py` by including its `.urls` property.

```python
viewset = WebsiteViewset()

urlpatterns = [
    path('', viewset.urls)
]

```

--------------------------------

### Add Vite Build Script to package.json

Source: https://docs.viewflow.io/crud/css_and_js.html

Configure your package.json file to include a script for running the Vite build process. This allows you to easily build your project's assets.

```json
"scripts": {
  "vite": "vite build"
}
```

--------------------------------

### Specify Source States

Source: https://docs.viewflow.io/fsm/options.html

Define one or multiple source states for a transition. Use a set for multiple states.

```python
from viewflow.fsm import State

@state_field.transition(source={States.NEW, States.DONE}, target=States.CANCELED)
def cancel(self):
    pass
```

--------------------------------

### User Task Configuration

Source: https://docs.viewflow.io/workflow/nodes.html

Represents a user interaction step in a flow. It can be configured with a view, annotations for display, permissions, and the subsequent node.

```python
class MyFlow(flow.Flow):
    ...

    approve = (
        flow.View(views.UpdateProcessView.as_view(fields=["approved"]))
        .Annotation(
            title=_("Approve"),
            description=_("Supervisor approvement"),
            summary_template=_("Message review required"),
            result_template=(
                "Message was {{ process.approved|yesno:'Approved,Rejected' }}"
            ),
        )
        .Permission(auto_create=True)
        .Next(this.check_approve)
    )

    ...
```
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