Workflow Without Windows Workflow

Hello, it has been a while since I wrote my last blog. Anyway, I am back again. I have a nice blog today, I have been working for a while with a team which his main target is to use everything Microsoft has released. It is a good thing sometimes and a very bad thing the other times. They read a "workflow" word in the requirements document, the first came to their mind was WF (Windows Workflow Foundation). The problem was so simple using WF would be over engineering. So, I decided to think of a more simple solution. As I am a Spring.NET Freak and I think we can't build an application without using it, I thought of using it :).

First, Let us create a State class first:

    public class State

    {

        private string _id;

        private string _name;

        private List<link> _links;

        public List NextStates

        {

            get

            {

                return Links.Select(l => l.State).ToList();

            }

        }

        public string Id

        {

            get { return _id; }

            set { _id = value; }

        }

        public List<link> Links

        {

            get { return _links; }

            set { _links = value; }

        }

        public string Name

        {

            get { return _name; }

            set { _name = value; }

        }

        public bool IsEndState

        {

            get

            {

                return Links.Count == 0;

            }

        }

    }

And a Link class:

    public class Link

    {

        //this condition will written used SPEL (Spring Expression Langauge)

        public string Condition { get; internal set; }

        public State State { get; internal set; }

    }

Then create the interface for the state machine:

    public interface IStateMachine

    {

        State InitialState { get; }

        State CurrentState { get; }

        void SetCurrentState(string id);

        bool Advance();

        List NextStates { get; }

    }

Then comes spring to the rescue, Spring here will used for 2 main tasks:

1. Configuration File for our Workflow (State Machine): Keeps the state information and the transitions between states.
2. Spring Expression will be used to define the transition rules between different states.

I decided to implement a simple interview process as an illustration for my small framework:

The spring configuration file for the mentioned process will be as follows:

<xml version="1.0" encoding="utf-8" ?>

<objects xmlns="http://www.springframework.net">

 

  <object id="ExamToFirstInterview" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="ExamScore >= 25"/>

    <property name="State" ref="FirstInterview" />

  <object>

  <object id="ExamToRejected" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="ExamScore < 25"/>

    <property name="State" ref="Rejected" />

  <object>

  <object id="FirstInterviewToSecondInterview" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="FirstInterviewAccepted"/>

    <property name="State" ref="SecondInterview" />

  <object>

  <object id="FirstInterviewToRejected" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="!FirstInterviewAccepted"/>

    <property name="State" ref="Rejected" />

  <object>

  <object id="SecondInterviewToAccepted" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="SecondInterviewAccepted"/>

    <property name="State" ref="Accepted" />

  <object>

  <object id="SecondInterviewToRejected" type="SimpleStateMachine.Link, SimpleStateMachine">

    <property name="Condition" value="!SecondInterviewAccepted"/>

    <property name="State" ref="Rejected" />

  <object>

  <object id="Exam" type="SimpleStateMachine.State, SimpleStateMachine">

    <property name="Id" value="exam"/>

    <property name="Name" value="Exam"/>

    <property name="Links">

      <list element-type="SimpleStateMachine.Link, SimpleStateMachine">

        <ref object="ExamToFirstInterview"/>

        <ref object="ExamToRejected"/>

      <list>

    <property>

  <object>

  <object id="FirstInterview" type="SimpleStateMachine.State, SimpleStateMachine">

    <property name="Id" value="first_interview"/>

    <property name="Name" value="First Interview"/>

    <property name="Links">

      <list element-type="SimpleStateMachine.Link, SimpleStateMachine">

        <ref object="FirstInterviewToSecondInterview"/>

        <ref object="FirstInterviewToRejected"/>

      <list>

    <property>

  <object>

  <object id="SecondInterview" type="SimpleStateMachine.State, SimpleStateMachine">

    <property name="Id" value="second_interview"/>

    <property name="Name" value="Second Interview"/>

    <property name="Links">

      <list element-type="SimpleStateMachine.Link, SimpleStateMachine">

        <ref object="SecondInterviewToAccepted"/>

        <ref object="SecondInterviewToRejected"/>

      <list>

    <property>

  <object>

  <object id="Accepted" type="SimpleStateMachine.State, SimpleStateMachine">

    <property name="Id" value="accepted"/>

    <property name="Name" value="Accepted"/>

    <property name="Links">

      <list element-type="SimpleStateMachine.Link, SimpleStateMachine">

      <list>

    <property>

  <object>

  <object id="Rejected" type="SimpleStateMachine.State, SimpleStateMachine">

    <property name="Id" value="rejected"/>

    <property name="Name" value="Rejected"/>

    <property name="Links">

      <list element-type="SimpleStateMachine.Link, SimpleStateMachine">

      <list>

    <property>

  <object>

  <object id="InterviewProcess.InterviewStateMachine" type="InterviewProcess.InterviewStateMachine, InterviewProcess">

    <property name="AllStates">

      <list element-type="SimpleStateMachine.State, SimpleStateMachine">

        <ref object="Exam"/>

        <ref object="FirstInterview"/>

        <ref object="SecondInterview"/>

        <ref object="Accepted"/>

        <ref object="Rejected"/>

      <list>

    <property>

    <property name="InitialState" ref="Exam"/>

  <object>

  <object id="SimpleStateMachine.IStateMachineManager" type="SimpleStateMachine.StateMachineManager, SimpleStateMachine">

  <object>

<objects>

Quite Simple? I think so :) Let us try it.

At the end I am not saying that this a replacement for windows workflow foundation is a very powerful framework but I am only pushing people to think outside of the box.

You can refer to the full source code here and don't forgot that I used Visual Studio 2010 Beta 2. Good Luck!

The initials of my blog are WWWW, isn't this cool? :D ... maybe this will be the next WWW ;).