stateful command pattern

Question

I was wondering what is the best way to represent an edit form in the context of domain model and I ended up with the command design pattern.

According to this: Using Command Design pattern commands should be immutable which is not what I need - I need stateful command with editable parameters (the whole command will be edited in ui/form)

Why is it considered to be bad to have stateful command?

EDIT: After some time it is now clear I was looking for the ViewModel pattern. That is the appropriate way to model any webapp screen. Basically it is stateful (per view instance) controller.

Have you tried implementing mutable commands? Did you hit unsolvable problems in the process? — fredoverflow, Feb 06 '11 at 15:05
No - I'm going to implement it I'm just wondering if there are no gotchas... — Kamil Tomšík, Feb 06 '11 at 15:08
@hvgotcodes: command pattern does not really require undo() - although it is the common use of command pattern (as well as rpc call is - and that is what kicked me into this solution) — Kamil Tomšík, Feb 06 '11 at 15:12
@kamil, my point was do you want to use the pattern so you can do undo? If so, you are using the wrong pattern. Use Mememto Pattern — hvgotcodes, Feb 06 '11 at 15:19
@hvgotcodes I don't I just want to represent future action with all of its parameters, I want to edit them using form and then execute action by clicking the ok button... — Kamil Tomšík, Feb 06 '11 at 15:21
That is a new command, generated by starting with a copy of an existing one. — Stephan Eggermont, Feb 10 '11 at 23:31
The question lacks important information about invoker and receiver and a specific use case to have answers other than "it depends on the problem". — Sascha Gottfried, Sep 27 '13 at 15:57

score 2 · Answer 1 · answered Feb 07 '11 at 19:27

2

You still want them to be immutable, because they can then be used to recreate the current state from a snapshot. But they can have all the parameters you want, as long as you make sure they cannot change after applying the command.

answered Feb 07 '11 at 19:27

Stephan Eggermont

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score 0 · Answer 2 · answered Dec 29 '12 at 17:57

if you want it mutable i would suggest using a FlyWeight Pattern instead. You can make it similar to a command pattern since its a hash of objects and it reuses the same objects if they exist already thus persisting the objects state.

You can think of FlyWeight as a group of singleton objects you can call on the fly (by a hash function).

So a flyweightfactory would house all your objects in a hash map and you could use the factory to retrieve the object maintaining its state.

http://www.avajava.com/tutorials/lessons/flyweight-pattern.html --> for anyone's reference.

stateful command pattern

2 Answers2