Control Flow logic understanding

[kadeer]

Hi. Thanks for the work on this awesome project.

We are considering Elsa to power some customization system in our application. Everything has quite awesome so far. However, we've hit this point of confusion, I'll describe here.

We have a workflow that has multiple boolean flags we'll like to check one after another and perform an activity or 2, for true outcomes ONLY, in the branch. So we have a what looks like the following...

	// ... previous activities

	.Then<IfElse>(
	    activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"),
		ifElse => 
			ifElse.When(OutcomeNames.True)
			    ... activities on true
		;
	).WithName("IfElse1")

	.Then<IfElse>(
	    activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"),
		ifElse => 
			ifElse.When(OutcomeNames.True)
			    ... activities on true
		;
	).WithName("IfElse2")

	.Then<WriteLine>(x => x.TextExpression = new LiteralExpression("End!")).WithName("End")

What we've noticed is that if condition1 evaluates to false, the workflow evaluation stops at IfElse1 activity. Our assumption was that the evaluator would continue to evaluating to IfElse2, and finally to End.

What's seemed to work so far, which seems quite :( is the following

	// ... previous activities

	.Then<IfElse>(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"),
		ifElse => 
			ifElse.When(OutcomeNames.True)
			... activities on true
			.Then("Label:0")
		;

		ifElse => 
			ifElse.When(OutcomeNames.True)
			// we dont have anything to put in here because this branch does not interest us
			.Then("Label:0")
		;


	).WithName("IfElse1")

	.Then<IfElse>(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"),
		ifElse => 
			ifElse.When(OutcomeNames.True)
			... activities on true.Then("Label:0")
		;

		ifElse => 
			ifElse.When(OutcomeNames.True)
			// we dont have anything to put in here because this branch does not interest us
			.Then("Label:0")
		;

	).WithName("IfElse2")

	.Add<Start>().WithName("Label:0")

	.Then<WriteLine>(x => x.TextExpression = new LiteralExpression("End!")).WithName("End")

Are we missing something that'd allow us maintain the simplicity of the first code block?
Thank you.

[sfmskywalker]

What you should do is continue with the if/else branching. You got it right with the second attempt (connecting to the next if/else using labels), but you can do it without by simply continuing within the if/else branches, like so:

// ... previous activities

.Then<IfElse>(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"), ifElse => 
{
    ifElse
        .When(OutcomeNames.True)
        .Then<IfElse>(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition2"), ifElse =>
        {       
            ifElse
                .When(OutcomeNames.True)
                .Then<IfElse>(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition3"), ifElse =>
                {
                    ifElse
                        .When(OutcomeNames.True)
                        .Then("End");
                });
        }
})

.Then<WriteLine>(x => x.TextExpression = new LiteralExpression("End!")).WithName("End")

We could make this a bit nicer though.

The Then<TActivity> automatically connects the activity to the previous activity using the "Done" outcome.

But we could implement an extension method e.g. WhenTrue that would call .Then<IfElse>.
That would allow you to rewrite the entire workflow like so:

.WhenTrue(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition1"))
.WhenTrue(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition2"))
.WhenTrue(activity => activity.ValueExpression = new JavaScriptExpression<object>("condition3"), falseBranch => { /* Maybe do something when things are false*/ })
.Then<WriteLine>(x => x.TextExpression = new LiteralExpression("End!"))

And in Elsa 2, you could replace the JS expressions with plain C# (statement) lambdas.