Comment by motorest
9 months ago
> "It's not object oriented programming" is only a good case to make if you think object oriented programming is synonomous with good. I don't think that's true. It's sometimes good, often not good.
See, this is the sort of lazy ignorance that adds nothing of value to the discussion, and just reads as spiteful adhominems.
Domain models are fundamentally an object-oriented programming concept. You model the business domain with classes, meaning you specify in them the behavior that reflects your business domain. Your Order class has a collection of Product items, but you can update an order, cancel a order, repeat an order, etc. This behavior should be member functions. In Domain-Driven design, with its basis on OO, you implement these operations at the class level, because your classes model the business domain and implement business rules.
The argument being made against anemic domain models is that a domain model without behavior fails to meet the most basic requirements of a domain model. Your domain model is just DTOs that you pass around as if the were value types, and have no behavior at all. Does it make sense to have objects without behavior? No, not in OO and elsewhere as well. Why? Because a domain model without behavior means you are wasting all development effort building up a structure that does nothing and adds none of the benefits, and thus represents wasted effort. You are better off just doing something entirely different which is certainly not Domain-Driven design.
In fact, the whole problem with the blend of argument you are making is that you are trying to push a buzzword onto something that resembles none of it. It's like you want the benefit of playing buzzword bingo without even bothering to learn the absolute basics of it, or anything at all. You don't know what you're doing, and somehow you're calling it Domain-Driven design.
> Why would focusing on OO be a goal?
You are adopting a OO concept, which the most basic traits is that it models business domains with objects. Do you understand the absurdity of this sort of argument?
> Domain models are fundamentally an object-oriented programming concept.
They are not.
> You model the business domain with classes, meaning you specify in them the behavior that reflects your business domain.
I have better tools for doing that.
> In Domain-Driven design, with its basis on OO, you implement these operations at the class level, because your classes model the business domain and implement business rules.
You're still not explaining the "why". You're just repeating a bunch of dogma.
> a domain model without behavior means you are wasting all development effort building up a structure that does nothing and adds none of the benefits, and thus represents wasted effort.
I know from experience that this is completely false.
> You don't know what you're doing, and somehow you're calling it Domain-Driven design.
I don't call it domain-driven. You can call it domain-driven if you want, or not if you don't want. I don't care what it's called, I care whether it results in effective, maintainable software with low defect rates.
> I care whether it results in effective, maintainable software with low defect rates.
This is what it is about. All the other things that have been invented need to be in service of this goal.
> I have better tools for doing that.
For example?
I would assume he meant to use the typesystem of his PL.
> Your Order class has a collection of Product items, but you can update an order, cancel a order, repeat an order, etc. This behavior should be member functions.
This is how to fuck up OO and give it a bad name:
What else could Order know about? Maybe give it a JSON renderer .toJson(), a pricing mechanism .getCost(), discounting rules .applyDiscount(), and access to customer bank accounts for .directDebit(); Logging and backup too. And if a class has 10+ behaviours you've probably forgotten 5 more.
An Order is a piece of paper that arrived in your mailbox. You can't take a sharpie to it, you can't tell it to march itself into the filing cabinet. It's a piece of paper which you.read() so that you.pack() something into a box and take it to the post office. You have behaviours and the post office has behaviours. The Order and the Box do not. At best they have a few getters() or some mostly-static methods for returning aggregate data - but even then I'd probably steer clear. For instance: if the Order gave me a nice totalPrice() method, it simplifies things for later right? Well no, because in TaxCalculator (not order.calculateTax()) I will want to drill down into the details, not the aggregate. Likewise for DiscountApplier.
> Does it make sense to have objects without behavior? No, not in OO and elsewhere as well.
It does, just like in the Domain (real-world Orders). Incidentally, I believe objects-without-behaviours is one of the core Clojure tenets.
Since this is HN's monthly UB-bashing thread, I should point out that I learnt most of this stuff from him. (It's more from SOLID though, I don't think I have much to say on about cleanliness.)
The above examples violate SRP and DI.
"Single reason to change": If order.cancel(..) knows about email, then this is code I have to change if the cancellation rules change or if the email system changes. What if we don't notify over email anymore? Order has to become aware of SMS or some other tech which will cause more reasons for change.
"Dependency inversion": People know what Orders are, regardless of technical competence. They can exist without computers or any particular implementation. They are therefore (relative to other concerns here) high-level and abstract. Orders are processed using a database, Kafka and/or a bunch of other technologies (or implementation details). DI states that abstract things should not depend on concrete things.
We have a disagreement about the core of OOP. In English, a simple sentence like "The cat eats the rat" can be broken down as follows:
- Cat is the subject noun
- Eats is the verb
- Rat is the object noun
In object-oriented programming, the subject is most often the programmer, the program, the computer, the user agent, or the user. The object is... the object. The verb is the method.
So, imagine the sentence "the customer canceled the order."
- Customer is the subject noun
- Canceled is the verb
- Order is the object noun
In OOP style you do not express this as customer.cancel(order) even though that reads aloud left-to-right similarly to English. Instead, you orient the expression around the object. The order is the object noun, and is what is being canceled. Thus, order.cancel(). The subject noun is left implicit, because it is redundant. Nearly every subject noun in a given method (or even system) will be the same programmer, program, computer, user agent, or user.
For additional perspectives, I recommend reading Part I of "Object-Oriented Analysis and Design with Applications" (3rd edition) by Grady Booch et. al, and "Object Thinking" by David West.
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That said, I think you're right about the single responsibility principle in this example. A class with too many behaviors should usually be decomposed into multiple classes, with the responsibilities distributed appropriately. However, the object should not be left behavior-less. It must still be an anthropomorphized object that encapsulates whatever data it owns with behavior.
> So, imagine the sentence "the customer canceled the order."
> - Customer is the subject noun
And this is wrong. Because the customer did not cancel the order. The customer actually asked for the order to be canceled. And the order was then canceled by "the system". Whatever that system is.
And that is the reason why it is not expressed as customer.cancel(order) but rather system.cancel(order, reason = "customer asked for it").
> Thus, order.cancel(). The subject noun is left implicit, because it is redundant.
Ah, is that so? Then, I would like you to tell me: what happens if there are two systems (e.g. a legacy system and a new system, or even more systems) and the order needs to be sometimes cancelled in both, or just one of those systems? How does that work now in your world?
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The comparison to English grammar is unnecessary. I didn't use it in my argument and you said it doesn't work that way either, so when you arrive at
> The order is the object noun, and is what is being canceled. Thus, order.cancel()
You've just restated the position I argued against, without an argument.
Aw, you described it so much nicer than me. I feel bad now.
> Domain models are fundamentally an object-oriented programming concept
They are absolutely not. In fact, they are not even specific to even just programming, let alone OOP.
I really don't understand this fixation on domain modelling. It looks like a lot of UML mixed with a "*DD" (life-pro tip: pretty much any X Driven Development is something experienced programmers rarely care about. You can borrow good ideas from almost any methodology without becoming obsessed with its primary subject. Being obsessed with the One True Way is a great way to waste a lot of brain cells). Also nobody sane touches UML. Or makes big official charts of classes and their relationships. It's a massive waste of time. You might come up with some core concepts and relationships, like a B-REP, but you don't need some jargon-heavy official way to do this.
> The argument being made against anemic domain models is that a domain model without behavior fails to meet the most basic requirements of a domain model. Your domain model is just DTOs that you pass around as if the were value types, and have no behavior at all. Does it make sense to have objects without behavior? No, not in OO and elsewhere as well. Why? Because a domain model without behavior means you are wasting all development effort building up a structure that does nothing and adds none of the benefits, and thus represents wasted effort. You are better off just doing something entirely different which is certainly not Domain-Driven design.
I have barely any idea what you're saying, but I will agree that I'm probably better off without DDD.
> You are adopting a OO concept, which the most basic traits is that it models business domains with objects. Do you understand the absurdity of this sort of argument?
Except I'm not, because I don't care about DDD? My argument is simply: caring how much your code adheres to some third party methodology doesn't matter, what matters is if you're writing good code or not.