Spot Flow

Spot Flow is a workflow engine for Rails applications based on the bpmn standard. It executes business processes defined in a modeler. It uses Spot Feel to evaluate expressions and business rules in the BPMN model. It can be used with Spot Form to render dynamic forms for user tasks.

Usage

The engine executes business processes like this one.

Example

Processes are made of a series of tasks. Tasks can be manual (require signal to be called) or automated (can be run by the engine). The engine supports the following task types:

  • Task and UserTask (manual): requires a signal to continue.
  • ServiceTask (automated): instantiates a type defined in the task definition and invokes call on it.
  • BusinessRuleTask (automated): evaluates the decision_id (expects dmn source to be included in the context).
  • ScriptTask (automated): evaluates the FEEL expression in the script property.

To start the process, initialize SpotFlow with the BPMN and DMN source files, then call start.

sources = [
  File.read("hello_world.bpmn"),
  File.read("choose_greeting.dmn")
]
execution = SpotFlow.new(sources).start

It's often useful to print the process state to the console.

execution.print

HelloWorld started * Flow_080794y

0 StartEvent Start: completed * out: Flow_080794y
1 UserTask IntroduceYourself: waiting * in: Flow_080794y
2 BoundaryEvent EggTimer: waiting

The HelloWorld process began at the Start event and is waiting at the IntroduceYourself user task. This is an important concept in the SpotFlow engine. It's designed to be used in a Rails application where a process might be waiting for a user to complete a form, or a background job to complete. It's common to save the state the process until a task is complete. Calling serialize on a process will return the execution state so it can be continued later.

# Returns a hash of the process state.
execution_state = execution.serialize

# Now we can save the execution state in a database until a user submits a form (UserTask)
# or a background job completes (ServiceTask)

# Restores the process from the execution state.
execution = SpotFlow.restore(sources, execution_state:)

# Now we can continue the process by `signaling` the waiting task.
step = execution.step_by_element_id("IntroduceYourself")
step.signal(name: "Eric", language: "it", formal: false, cookie: true)

After the IntroduceYourself task is signaled, the execution continues.

HelloWorld started * Flow_0gi9kt6, Flow_0pb7kh6

{
  "name": "Eric",
  "language": "it",
  "formal": false,
  "cookie": true
}

0 StartEvent Start: completed * out: Flow_080794y
1 UserTask IntroduceYourself: completed { "name": "Eric", "language": "it", "formal": false, "cookie": true } * in: Flow_080794y * out: Flow_0t9jhga
2 BoundaryEvent EggTimer: terminated
3 ParallelGateway Split: completed * in: Flow_0t9jhga * out: Flow_0gi9kt6, Flow_0q1vtg3
4 BusinessRuleTask ChooseGreeting: waiting * in: Flow_0gi9kt6
5 ExclusiveGateway WantsCookie: completed * in: Flow_0q1vtg3 * out: Flow_0pb7kh6
6 ServiceTask ChooseFortune: waiting * in: Flow_0pb7kh6

When execution reaches the Split inclusive gateway, it forks into two paths. The first path is waiting at the ChooseGreeting business rule task. The second reaches the WantsCookie exclusive gateway and evaluates the sequence flow conditions before continuing to the ChooseFortune service task. Automated tasks can be run individually by the engine or run_automated_tasks to run all waiting tasks.

execution.run_automated_tasks

Now, both paths are joined into one and execution is waiting at the script task. Notice, the results of previous tasks are merged into the process variables.

HelloWorld started * Flow_0ws7a4m

{
  "name": "Eric",
  "language": "it",
  "formal": false,
  "cookie": true,
  "choose_greeting": {
    "greeting": "Ciao"
  },
  "choose_fortune": "A foolish man listens to his heart. A wise man listens to cookies."
}

0 StartEvent Start: completed * out: Flow_080794y
1 UserTask IntroduceYourself: completed { "name": "Eric", "language": "it", "formal": false, "cookie": true } * in: Flow_080794y * out: Flow_0t9jhga
2 BoundaryEvent EggTimer: terminated
3 ParallelGateway Split: completed * in: Flow_0t9jhga * out: Flow_0gi9kt6, Flow_0q1vtg3
4 BusinessRuleTask ChooseGreeting: completed { "choose_greeting": { "greeting": "Ciao" } } * in: Flow_0gi9kt6 * out: Flow_1652shv
5 ExclusiveGateway WantsCookie: completed * in: Flow_0q1vtg3 * out: Flow_0pb7kh6
6 ServiceTask ChooseFortune: completed { "choose_fortune": "A foolish man listens to his heart. A wise man listens to cookies." } * in: Flow_0pb7kh6 * out: Flow_1iuc1xe
7 ParallelGateway Join: completed * in: Flow_1652shv, Flow_1iuc1xe * out: Flow_0ws7a4m
8 ScriptTask GenerateMessage: waiting * in: Flow_0ws7a4m

This time we'll run the script task manually.

step = execution.step_by_element_id("GenerateMessage")
step.run

Now the process is complete.

HelloWorld completed *

{
  "name": "Eric",
  "language": "it",
  "formal": false,
  "cookie": true,
  "choose_greeting": {
    "greeting": "Ciao"
  },
  "choose_fortune": "A foolish man listens to his heart. A wise man listens to cookies.",
  "message": "👋 Ciao Eric 🥠 A foolish man listens to his heart. A wise man listens to cookies."
}

0 StartEvent Start: completed * out: Flow_080794y
1 UserTask IntroduceYourself: completed { "name": "Eric", "language": "it", "formal": false, "cookie": true } * in: Flow_080794y * out: Flow_0t9jhga
2 BoundaryEvent EggTimer: terminated
3 ParallelGateway Split: completed * in: Flow_0t9jhga * out: Flow_0gi9kt6, Flow_0q1vtg3
4 BusinessRuleTask ChooseGreeting: completed { "choose_greeting": { "greeting": "Ciao" } } * in: Flow_0gi9kt6 * out: Flow_1652shv
5 ExclusiveGateway WantsCookie: completed * in: Flow_0q1vtg3 * out: Flow_0pb7kh6
6 ServiceTask ChooseFortune: completed { "choose_fortune": "A foolish man listens to his heart. A wise man listens to cookies." } * in: Flow_0pb7kh6 * out: Flow_1iuc1xe
7 ParallelGateway Join: completed * in: Flow_1652shv, Flow_1iuc1xe * out: Flow_0ws7a4m
8 ScriptTask GenerateMessage: completed { "message": "👋 A foolish man listens to his heart. A wise man listens to cookies." } * in: Flow_0ws7a4m * out: Flow_0gkfhvr
9 EndEvent End: completed * in: Flow_0gkfhvr

Documentation

Installation

Execute:

$ bundle add spot_flow

Or install it directly:

$ gem install spot_flow

Development

$ git clone ...
$ bin/setup
$ bin/rake
$ bin/guard

License

The gem is available as open source under the terms of the MIT License.

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