Load workflow specification from YAML file?

[abhas]

I'm trying to build a user extensible workflow. So I wanted to check if there are any plans on building functionality to load the workflow specification from a YAML file?

I would love to work on this myself if you could give some pointers on how to get started.

[geekq]

A workflow is definied by a Specification object.

Normally it is created with workflow do ... end, but it should be also possible to create it on the fly by serializing/deserializing Workflow::Specification from yml file.

We will presumably have to separate the workflow method into 2 parts. Will refactor and get back...

[geekq]

Just extracted the assign_workflow method 556f5a6

To do what you want to do please create Workflow::Specification in some way, e.g. from definition in yml file. Then call assign_workflow.

[abhas]

Thanks a lot, Vladimir. This really helps. I'll try this out and provide feedback to you.

[mvaragnat]

Hello @geekq I see this old issue, matching my exact business need
Has it been closed because already implemented, or because it was too complicated / out of scope ? If so, do you have a workaround to suggest ?

[geekq]

You need:

1. to prepare a workflow specification object
2. call assign_workflow

As explained in the 68951c9 example, you can load a specification object from yaml, then run assign_workflow https://github.com/geekq/workflow/blob/develop/lib/workflow.rb#L30

Or you maybe want to load your specially designed yaml and then call methods on the spec object like

mystates = [:foo, :bar, :baz] # here hard coded, but you can load from yaml file too
myspec = Workflow::Specification.new do
  mystates.each do |s| # iterate through the list loaded from yaml
    state s do
      event :foobalize, :transitions_to => :foo # we want each state to have a transition to :foo
    end
  end
end
myspec.states.length # you see you have 3 elements here - loaded from the array

The requirements on which workflow aspects, and how to be represented in yaml, may vary greatly. So they are better implemented in your application specific code.

[mvaragnat]

Thanks, very clear on the Specification part

My next question is where to call assign_workflow.

So let say I have a BusinessProcess model, intended to represent various workflows, each modelized in a yaml.
Can each instance of business_process can load a different yaml ?

class BusinessProcess < ApplicationRecord
  include Workflow
  
  assign_workflow load_spec_from_yaml(path: self.yaml_path)
  
  def load_spec_from_yaml(path:)
    states = Yaml.safe_load(path)
    return Workflow::Specification.new do
      # some magic inspired from your reply above
    end
  end
end

process1 = BusinessProcess.new(yaml_path: 'docs/myfile1.yaml')
process2 = BusinessProcess.new(yaml_path: 'docs/myfile2.yaml')

something like this ?

[geekq]

I recommend https://www.manning.com/books/the-well-grounded-rubyist-second-edition book to learn about advanced, class level- and meta-programming.This is very good!

One user #55 (comment) also recommended http://ruby-metaprogramming.rubylearning.com/ (I have not read this one myself though)

For multiple workflows please also see the example https://github.com/geekq/workflow-activerecord/blob/develop/test/multiple_workflows_test.rb

# define workflow per object instead of per class

[tlloydthwaites]

This is pretty straight-forward, I achieved it like this:

c = Class.new
c.class_eval do
 include Workflow
end

hash = {
 state_1: {
   events: {
     event_1: {
       transition_to: :state_2,
       if: :event_1_condition?,
       meta: { e1: 1 }
     },
   },
   meta: { a: 1 }
 },
 state_2: {
   meta: { a: 2 }
 }
}

spec = Workflow::Specification.new {}

hash.each_pair do |state, state_def|
 spec.send :state, state, state_def
 state_def[:events]&.each_pair do |event, event_def|
   spec.send :event, event, event_def
 end
end

c.send :assign_workflow, spec

o = c.new
puts o.current_state
puts o.current_state.events