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I have an object which represents some document stored in a relational database (O/R mapping). This document has a status field which identifies its state. Every status (ie. entry, wait for approval, sent, paid etc...) carries it's own validation rules and requirements.

I'm wondering what is a correct OO implementation of such workflow. The easiest way of doing it is placing a bunch of if statements like

if (status == something || status == something else) check if the date can be changed();

but in a complex scenario this becomes extremely hard to read.

Suggestions for good design?

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  • well the wf or life-cycle of your doc should not only exist in the UI level to enable/disable some buttons, it should be known also at Businee Logic level so that the logic can react properly and trigger certain actions. I would have a look at WF (Microsoft Workflow Foundation), it's configurable and should server the need (and even more) ;-) Commented Jan 16, 2012 at 10:35

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Have a look at the Strategy Pattern. For each possible state you would create a class implementing the steps to perform.

Maybe you want to combine it with a Factory that builds the correct strategy object depending on the state of the doucment when it is read from the DB.

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Thanks. I'll look into it. Just a question if you're already familiar with it - Classes that represent each state are internal (nested in) to the document class?
I don't have enough knowledge of your concrete design, I wouldn't implement it that way (especially if the documents are persistent as in your case). The strategies should operate on the documents and modify them
Disadvantage of this approach as I see it is that all internals of Document class are hidden from a 'State' classes.
Disadvantage mentioned above is successfully solved by declaring strategy classes nested which will give them fully access rights to a parent class.
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I think you need to review Windows Workflow Foundation. It's part of .NET and it's gives you ability to create workflows relatively easy.

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Workflow will not change once it's implemented. I need an easy and clear way of implementation and introducing a new technology will not help in this regard IMO.
Just preview it and I'm sure boss/customer may like it...WWF just amazing thing :)

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