Someone has to say it: Damn, this looks fucking ridiculous!
First we have the false modularity. You see a bunch of separate stuff (classes, methods, whatever) and think "Wow, nice, now we can reuse this all over the place!" The truth is that these policies/services/renderers are going to be complected; you're going to create them in triplets as you implement your application. Moving things around doesn't make them modular. They can only be modular if the author actually implements them in a modular way (and you can do that in Rails today).
The DI-framework can't handle change at all:
class CurrentUserResolver
def initialize(user_finder = User)
@user_finder = user_finder
end
# note that resolvers themselves get injected
def call(session)
@user_finder.find_by_id(session[:current_user_id])
end
end
What if I later need the cookies/params to detect user session? If I changes the #call method, every single test breaks.
And then there's the added complexity. Now I need to keep track of the route-mapping, default policy, route policies, the route service and the route renderer. Which are now in several different files. And there's not even a clean class-to-file mapping to help me locate it.
Oh, and the premise of testability. Well, this makes it very easy to test units itself, but the more you split your projects into smaller units, the more bugs occur when you mix the units. Sure, you can get your precious fast test runs (and a nice green test), but in reality you're only testing a single unit of a complected app.
EDIT: This reminds my of Rick Hickey's quote from keynote at RailsConf2012:
""We can make the same exact software we are making today with dramatically simpler stuff—dramatically simpler languages, tools, techniques, approaches. Like really radically simpler—radically simpler than Ruby which seems simple.""
You'll have to decide if he made his case or not, but if that's what he thinks then better he just come right out with it instead of dancing around.
Note that he did not call James ridiculous, he criticized the idea. Which is how it should go (if there's going to be criticism).
You can debate whether his assertion is justified, but some (many, perhaps) ideas really are fucking ridiculous and it's better to just cut to the chase.
This is not object-oriented at all, unless you learned about object-orientation from Java and its monster frameworks, this is basically a form of data-flow programming. OO is about message passing, here the "objects" do not pass any messages at all, the supposed "objects" _are_ the messages, and the routing of those messages takes place in the configuration in routes.rb, so the objects do almost no message-passing between themselves at all! It is ironic to see this advertised as "better OOP practices for rails apps".
Having said this, I respect the attempt, the problem it tries to solve certainly does exist to some extent, and the solution cannot be completely dismissed very easily.
But please, please, do learn both A) basic history and B) basic theory of the field you are working in. If you try to reinvent everything you decrease your chances of contributing something new manyfold.
I've read at least a dozen papers on the history of OO, not to mention books and papers on current practices. This is what I came up with. I made what I think is a pretty coherent argument for why in the article. I'd love to hear your refutation of the points I made in there.
You have to think a bit more about what OO really is about. How would properties of your solution differ if you instead of classes split all the code into many very small global methods? The essence of OO is objects freely passing messages between themselves, if you fix all the message routing and put it in a central place you are not doing OO anymore, you loose the most fundamental properties, for example:
You also don't have encapsulation anymore, since to be able to perform the majority of the work in the services, the services have to operate directly on data owned by other objects.
How can you combine the policies in ways other than a simple logical AND? How do you combine services?
Others have also already pointed out other issues.
Please don't be offended by the above. Software engineering is unfortunately a field where some valuable content is buried underneath loads of BS, since it is so easy to "philosophize" about it even with just basic programming experience and this leads other people learning the field to easy misconceptions. I do not want to discredit the work you put into this and it might be that in some form something valuable will come from some of the ideas. It is an interesting problem to work on and for me it was an interesting solution to think about, I just don't think you are there yet.
> You have to think a bit more about what OO really is about.
If you want to have a respectful debate, I'm completely game. If you'd prefer to continue with your incredibly condescending tone, then I'll bow out here.
Well, maybe I got carried away a bit with the tone in general in the last paragraphs of both comments, but I think I substantiated the particular sentence you cited quite a bit. On the other hand, I also took half an hour to clearly explain to you why this is somewhat misguided and tried hard to be polite, while someone below just said "this is fucking ridiculous". It's hard, at least for me, to give constructive criticism, without the other person being offeneded.
No. It may be unintentional, but the tone of stiff's comments is highly condescending.
Exhibit A: Whatever you think about James's choices in this library, he has clearly thought a lot about OOP. It's just silly to start a comment with "You have to think a bit more about what OO really is about."
I think what the GP might be trying to get at is this: you've reinvented partial function application and first-class functions. An instance of a class can be regarded as a bundle of functions which all have the constructor's parameters partially applied. If your instance only has one method, it's equivalent to a single, partially applied function. In that sense, what you've done is found a way to reorganise a Rails app in a very functional way - and, if you want to do that, given that Ruby doesn't have first-class functions or partial application (well, without proc hack, anyway), this may be the best way to do it.
It may work very well, but it's at least as functional as it is OO.
From the examples it doesn't even look like a _partial_ function application since it is not clear whether you can control how those services/policies/responders are initialized. Also I think it would be quite awkward for one service to initialize another and call it, so it is not really functional programming either, since there are no direct function calls. Since all the flow of the data is described in the routes file, it isn't OO at all and mostly reassembles dataflow programming as I said:
Parts of this approach might be valuable, as I tried to emphasize, but as a whole this doesn't look good for plenty of reasons mentioned in the thread.
The CurrentUserResolver example in the README shows that some initialisation control is possible here.
> it is not really functional programming either, since there are no direct function calls.
There don't have to be. The classes and instances are being referred to by the developer in the same way as any first-class functions defined elsewhere would be - they're actually resolved and called by the framework.
> Since all the flow of the data is described in the routes file, it isn't OO at all and mostly reassembles dataflow programming as I said
It certainly is OO. There are instances, and they receive and act on messages. Yes, there's a dataflow-like DSL for routing, but that's not to the exclusion of other paradigms.
The CurrentUserResolver example in the README shows that some initialisation control is possible here.
This is the dependency injection part, not the policy/service/responder core of the framework I am talking about.
There don't have to be. The classes and instances are being referred to by the developer in the same way as any first-class functions defined elsewhere would be - they're actually resolved and called by the framework.
I am not talking about what happens on the level of Ruby, I am talking about what happens logically at the level of the framework. The classes represent functions, sure, but they do not call other functions (services/policies/responders), the only "function-calling" is done by the router. Yes, this too is a form of functional programming, the form known as dataflow programming where the flow of the data is described explicitly.
It certainly is OO. There are instances, and they receive and act on messages. Yes, there's a dataflow-like DSL for routing, but that's not to the exclusion of other paradigms.
It isn't OO at the level of the framework. Yes, Ruby is underneath, there are classes, there are instances, and the thin ORM layer is object oriented, but the objects within the framework do not exchange messages, the only object doing all the message dispatch is the router. This is not OO, just look at the traits listed here: http://en.wikipedia.org/wiki/Object-oriented_programming
The framework basically forces you to abandon messaging (since there is no exchange of messages, just single directional messages flow from the router), abandon encapsulation (since the services have to access the data of the domain objects and hence the domain objects must make their data available to everyone) and abandon polymorphism (since the services are statically dispatched by the router). How can this be object oriented?
I don't think there is a single right answer that is applicable in all cases. But over time, I've come to believe that as a default, code works well when it resembles how you'd ideally explain the service to an extremely intelligent, non-technical person with domain experience. This makes for code that is easy to understand, collaborate around, and modify given changing objectives.
That means creating "Policy" and especially "Service" models--extra nouns--very sparingly. For example, an Elevator was once a nounification of a verb, but people understood it, so it makes sense as a class. ElevatorDoor's good too, but ElevatorDoorOpeningService is probably not good. This is absolutely at odds with strict application of the Single Responsibility Principle.
This idea of having an ubiquitous domain language and keeping applications and APIs RESTful have been two of the most beneficial ideas I've incorporated into my development in recent years.
Likewise I disagree with the idea that these two projects share the same space. A Java ORM and a Rails metaframework for avoiding ORM are not things which have a lot in common. I think the last time I observed a Rails hacker saying anything about AppEngine was 2007 or something.
It will certainly cause confusion. This is just decidedly uncool.
As the lead developer of the Objectify project, and someone who makes a living through consulting related to Objectify, I am highly annoyed. I'm also talking to a trademark attorney to find out my options.
Jesus, dude, why not just talk to OP instead? Any lawyer will tell you that if you can resolve your differences peacefully out of court, you should. This seems to be some kind of hair-trigger litigiousness thing you've got on going here.
Relax, it's not like I'm setting a court date. I just prefer to know where I stand before I open my mouth, and I happen to work with lawyers who specialize in this kind of thing. Research before action, no?
Why are people building frameworks to sit on top of yet another framework to try to write cleaner more maintainable code???
What is wrong with writing your core application logic physically removed from any of these frameworks. Why do people insist on fitting their application into the Rails framework or any other web framework.
Write your core application code in Ruby (or your language of choice), package it in another gem, use tools and patterns we've had all along to plug that code into a dependency for persistence (if needed)...communicate with it through a standard API that you define for your delivery mechanism (i.e. Rails).
I just don't get this idea of trying to contain my application code within the confines of a specific framework.
"Single responsibility principle (SRP): ... ActiveRecord::Base already has a responsibility: persistence."
Wrong. I'm hearing this more and more, but let's be clear: Active Record as a design pattern, before Rails, has always been a joining of business logic and persistence. (http://martinfowler.com/eaaCatalog/activeRecord.html) It's always been in violation of the single responsibility principle. If you want to avoid that, don't use Active Record! Use a Data Mapper, which specifically separates Mappers and Finders from Domain model classes. (http://martinfowler.com/eaaCatalog/dataMapper.html)
I'm not saying you can't move logic out into reusable modules or whatever is being recommended here, but please don't make it out like people are in the wrong when they're using the library or framework the way it was designed to be used.
The reason I don't like adding extra methods to classes is because by doing so you often end up adding an extra layer of dynamic dispatching. If I have that functionality in a static function when I read it I know that it can only do one thing but if I see a method call I have to always wonder if its going to be polymorphic.
At first I thought this was an attempt at trolling, but then I noticed that Mr. Golick is the commenter so therefor I must assume serious intent.
Care to give an answer better than "some book some java dudes wrote 20 years ago said so"?
While I generally agree with SRP, when that single responsibility can be expressed in a single function, I don't see the win with have a class dedicated to it. Smells of pedant OO nonsense.
Is not instantiation etc a cross-cutting concern that violates SRP in this instance?
"some book some java dudes wrote 20 years ago" — If you're referring to "Design Patterns", the Gang of Four were writing about C++, it was 1994, and Java wasn't out yet.
I think you misunderstood each other, you meant a global method and Mr. Golick seems to have understood that you mean just another method in the controller or whatever.
Also, those are not really single-method classes, but single-method interfaces. Since you didn't give any arguments, I don't see how those two extra lines to define a class have any disadvantage in comparison to a global method, and having the framework define a interface to program to leaves more flexibility to the framework user than having the framework accept a method name or block instead. The instatiation of the class can be left to the framework user (in general, I don't know if this is the case here in particular) so that additional data can be attached, inheritance can be used (yes, inheritance has its problems, still it also has plenty of valid usage scenarios), methods broken down into smaller private methods etc. Also in Ruby there are no global methods like you would have in Python or C++, you always define a method of some class, even if it's in the top-level scope - files almost always correspond to individual classes so it would be pretty odd to have methods used here instead.
> Is not instantiation etc a cross-cutting concern that violates SRP in this instance?
Right.
Which is why hes also recommending the use of DI.
It's hard to strike a balance between a strong design which takes a lot of time to work within, and one that just allows you to get things done, but once your project begins to grow in size and complexity, and testing becomes even more important, these things really do start to matter.
It's difficult to internalize until it's bitten you on the ass, hard.
That said, if you have a large amount of single method classes, you might need to take a look at why you need them and find a better approach (which will vary from project to project).
> It's hard to strike a balance between a strong design which takes a lot of time to work within, and one that just allows you to get things done, but once your project begins to grow in size and complexity, and testing becomes even more important, these things really do start to matter.
The whole point of objectify is that it actually makes it pretty reasonable to work this way right off the jump. I would have a hard time believing that it's really any more work to build an objectify app than it is to build a vanilla rails app - at least once you become accustomed to the paradigm.
> That said, if you have a large amount of single method classes, you might need to take a look at why you need them and find a better approach (which will vary from project to project).
I don't buy that. My project has hundreds of single method classes and it's by far the best factored non-trivial application I've ever seen (anecdotal, obviously, but so it goes).
>The whole point of objectify is that it actually makes it pretty reasonable to work this way right off the jump. I would have a hard time believing that it's really any more work to build an objectify app than it is to build a vanilla rails app - at least once you become accustomed to the paradigm.
Sure. I wasn't saying otherwise. What I meant was, in a general sense (prior to really seeing the benefits first hand), it can be hard for people to justify the trade off when they feel like they can just "get it done faster" with a more ad-hoc approach to things. I didn't mean to imply Objectify was some how more difficult (I haven't used it, so I wouldn't dare comment on it in such a way).
>I don't buy that. My project has hundreds of single method classes and it's by far the best factored non-trivial application I've ever seen (anecdotal, obviously, but so it goes).
Agree to disagree, with a caveat. I'm not against having a large amount of "Helper" or in the case of what I'm most familiar with, "Extension" classes (godbless you, .NET Extension classes), but I think if you have so many that they comprise most of your code base, maybe you could consolidate some of them (and maybe you couldn't).
Personally, I try to keep 100% of my core business logic inside of "Service" style classes, and then anything that is more of a helper (in that it performs some work, but not "business logic", and does not require or alter internal state) in either a static helper, or an Extension on the type itself.
For example, I usually end up adding a .ToStart/EndOfDay/Week/Month suite of methods to the datetime object of most of my projects. A "DateTime Service" would be overkill, but an extension method (which is just veneer over a static helper) fits the model perfectly, in that it returns a new copy of the existing datetime, leaving the original intact.
But at this point we're getting pretty deep into the comment tree, so feel free to email me from my profile if you want to go more into the issue - I love shooting the shit over this kind of stuff. Regardless of any minor difference of opinions, I think what you're trying to bring to the rails community is to be commended.
I can see how that will give you a single-method class some of the time, and I'm in absolute agreement as to how it applies to serialisation classes, but I don't see how SRP implies that single-method service and policy classes are the One True Way.
I think I'll have to give objectify a try and see how it all fits together. It's a different enough approach to what I'm used to that I probably don't have a reliable intuition as to how it'll turn out in practice.
When I was first trying to learn about rails, I asked a friend who had been developing in it for a while about things like DI, and separation of concerns. He told me that those were things you used in Java and .Net because the languages just weren't as... I'm struggling to remember the exact term he used, but essentially "open" or "un-restricted".
He echoed the phrase I've seen elsewhere "Ruby just doesn't need that".
I disagreed with him then, and still do. People like to claim that OOP breeds cargo cult programming and overly cumbersome abstractions upon abstractions (and it can), but some times you really do need that kind of approach to make a large scale project testable and maintainable.
I'm glad to see there are Ruby devs who can see the value in using these kind of approaches. I honestly believe it's the kind of thing you think is a major waste of time, until you are shown the benefit first hand, and you experience the change. Then you start to understand that by spending a significant deal of time up front building your infrastructure, you can save a lot of time down the road.
Objectify is a nice framework, but after reading the examples in README made me feel like I am required to take extra iterations: create new responder files, write more codes for each Responder class, etc. This approach is little tedious.
I personally think that writing reusable libraries using Decorator/Presenter patterns or Modules with ActiveSupport::Concern is simple approach.
As can be implied by the title, one of the side effects of keeping your service logic in their own separate plain Ruby classes is that you don't have to load Rails as dependency which means tests can run _really_ fast.
Isn't this the command pattern, except instead of 'execute' you use 'call'?
Update: not saying that's a bad thing I used to be a Flex developer and all the frameworks used MVCS (Robotlegs being my favorite). Controllers are all commands and Services are used to retrieve data.
"The more responsibilities an object has, the more complex its behaviour becomes, and is therefore more difficult to prove and reason about."
Emphasis mine. I don't think this has to be true. Yes, models get fatter, but the responsibilities will have to be implemented somewhere and to me it's simpler and easier to debug when it's as close to the domain model as possible instead of in some abstract/generic model.
Of course, if you have policies and services that apply across domains, then by all means break them out and recompose as necessary in the the models
Not quote Donald K. but I've seen my share of optimizing rails apps that points to the fact that each class added is extra 2-4 megs of RAM. This sort of discouraging rule, looking ahead writing well tested app that does follow SRP and other nifty "literate" practices might cost you big time, tell me if I am wrong.
You can move over slowly by building new components using objectify, and leaving the rest of your legacy app the way it is, if you like. It's designed specifically to be able to coexist with what you've got.
I don't get why these models get bloated. If there's a language that makes it east break up classes into any number of components, surely that's Ruby! Mixins, open classes, modules, etc..
Mixins/modules and open classes do not separate your class in to multiple components - merely multiple files. As I explain in the article, for separate components to be useful, they have to be "protected" from each other - encapsulation, in other words.
Mixins (well, as they're supposed to be used) do provide encapsulation; specifically, they enforce the boundary between instance scope (e.g. access to instance vars) and method interface. I view them as a part of a coupling continuum:
But Modules provide more than that. module_function allows for unattached namespaced functions which can be referenced by full name, relative name, or imported into the local scope. Great way to express functions which are decoupled from instance state--much like the services and policies you're advocating for. It's an under-appreciated aspect of the language, I think.
I find that ruby projects end up breaking things up into modules, but fail to gain much benefit from it, since there's a tendency for the logic from the different "modules" to be tightly coupled. It's actually really hard to refactor ruby, since because it's so dynamic and so much state is shared, it's very hard to make safe changes.
Does this actually perform faster by being on top of rails or would we need a new Ruby framework to get the most speed optimizations from the services and policies?
I have a prejudicial assumption that if you don't know the problem Objectify solves, you haven't worked with a Rails app which has A) a large code base B) a large, active user base and C) a bunch of different features.
The vast majority of people who scale Rails sites (as far as I can tell) do so by breaking their apps into services. ActiveRecord god-objects do not make that step in an app's life cycle easy, and separating persistence from business models is likely to be your first important step when refactoring for scalability. Fragmenting a User model bloated beyond all hope of sanity is almost a rite of passage at this point.
I often think the only Rails developer who hasn't found ActiveRecord bloat to be an irritation and an obstacle to scaling is DHH, and although that makes his opinion on the subject even more valuable than it would normally be, he doesn't talk about it enough in my opinion. Pretty much everyone else, as far as I can tell, responds to Rails scaling issues by creating services in Sinatra and/or divorcing business modeling from persistence logic.
I want someone to challenge my prejudicial assumption here, most of all because I appear to be saying "Rails can't scale," which is BS, but also because I'm very tempted not to take this discussion seriously at all if it doesn't address this point. It's just the crucial point in my opinion. I like the whole OOP thing but to me the decision to use something like Objectify is all about scalability. That doesn't just mean performance; it also means retaining readability when you have a lot of code. Single Responsibility Principle makes code readable.
I worked in Rails for the last 6 years professionally, and for the last 4 years on a single application. There are lots of ways to tackle this problem, but it really depends what precisely you have inside those models and there are certainly no universal silver bullets. Lots of people who complain about this underuse Rails features, external plugins etc. I think two good ways to deal with the problem are:
- Splitting out logical pieces of behaviour into separate modules, especially the ones less central to the core responsibilities of the class. If you look at Rails itself (it's great Ruby code, I highly recommend really reading it), this is the way it is structured, ActiveRecord::Base provides tons of functionality as a single class, yet it still is very neatly laid out into many well-separated modules. See e. g.:
Deciding what things would fit well into external modules and what modules to create is a new skill to be learned, but I think it can work well once you do learn it.
- Things that aren't part of business logic but just handle some more technical matters should be extracted into plugins and not be directly part of the models (for example: special kinds of validations).
- There is the whole world of OO techniques and patterns that can be applied here just like anywhere else. For example you can extract complicated algorithms into separate classes or use value objects:
"If you look at Rails itself (it's great Ruby code, I highly recommend really reading it)"
I've worked with a member of Rails core, and frequent committers. I've spoken at 10 Ruby conferences at least, maybe 20. I'm familiar with the Rails code base. I once rewrote a few small pieces of ActiveRecord from memory for a stupid project because my wifi was dead.
I agree about it being worth reading, I just want to slow you down there for a second. Otherwise we're going to end up pulling things out and measuring them. I took the time to check your links, although I'd seen most of them already. I'm familiar with concerns and although I think your links are germane I'd have to disagree with this part:
"Deciding what things would fit well into external modules and what modules to create is a new skill to be learned"
As I think I've learned the skill.
What I'm saying basically is that I think you missed the mark in terms of guessing my background but I believe it was an honest mistake.
Egos aside, I agree that modularity matters. And I must admit I had a painful reminder about that skill recently when I built something around ActiveRecord and then refactored ARec out of the picture for performance reasons (the gains were staggering). It would have been less painful with better modularity, but I don't think the pain relief from using concerns would have been particularly great in this instance. Non-zero, but insignificant.
I don't care that much about OOP theory, but the pragmatic issues Objectify addresses seem to come up for people all the time. A year ago Steve Klabnik and a few other people were talking about this and I noticed it then how it was echoing James Golick's (the OP) posts about limiting ActiveRecord's role from a few years before that.
There basically seem to me to be three trends in discussion of scaling Rails: 1) "Rails can't scale" FUD, 2) DHH saying "just add hardware and/or caching", and 3) this idea of decoupling persistence from modeling, basically, reining in ActiveRecord, which I've heard from people like James Golick, Steve Klabnik, Gary Bernhardt, and I think Xavier Shay. Paul Dix wrote a great book about making Rails apps service-oriented, the Thoughtbot guys touch on it in their antipatterns book as well, and it's not exactly a coincidence that for many Rails apps the only gem more crucial than ActiveRecord is Delayed Job or Resque.
When I say "If you look at Rails itself" I do not mean you in particular, I mean in general for people wondering about the problem a good lesson is checking out the Rails code, similarly "a new skill to be learned" in the sense that it is different from traditional OO modelling most people come from. I know your blog and I've seen you discussing concerns in some other place, so I do appreciate your background. Maybe being irritated about bad ideas makes me come up more abrasive than usual.
Anyway, the whole discussion so far was about dealing with the problem of large (in terms of code size) models, so I assumed by "scalability" you mean scalability in terms of being able to handle very large code bases, not performance issues. I do not understand how the approach presented here would result in performance improvements? I've commented elsewhere on the problems associated with it, others did as well in a fairly convincing way I think. I do not deny that problems with scaling both in the performance sense and in the code size sense do exist, I just do not see how Objectify solves any of them and I do see how many problems it introduces.
As for breaking your app down into separate HTTP services, I agree this can be useful in some situations, but it is completely different from the approach outlined in Objectify, for one you still get a chance to do (almost) normal OO modelling and structure the code in a reasonable way, even if the message passing is done via HTTP and not simply via Ruby method calls.
FWIW, I'm not a Rails developer; so take my comments as you will.
I don't think the problem people seem to have with Objectify is that they see it as a totally invalid solution to a problem--and I agree with your assessment that many people see this problem as very real.
My own take is that I find it disingenuous to call it an Object-Oriented solution to the problem; it's not. That doesn't make it bad, invalid, or wrong. It rightly raises a few eyebrows to talk about effectively calling namespaced procedures as if it were the pinnacle of Object-oriented design.
First we have the false modularity. You see a bunch of separate stuff (classes, methods, whatever) and think "Wow, nice, now we can reuse this all over the place!" The truth is that these policies/services/renderers are going to be complected; you're going to create them in triplets as you implement your application. Moving things around doesn't make them modular. They can only be modular if the author actually implements them in a modular way (and you can do that in Rails today).
The DI-framework can't handle change at all:
What if I later need the cookies/params to detect user session? If I changes the #call method, every single test breaks.And then there's the added complexity. Now I need to keep track of the route-mapping, default policy, route policies, the route service and the route renderer. Which are now in several different files. And there's not even a clean class-to-file mapping to help me locate it.
Oh, and the premise of testability. Well, this makes it very easy to test units itself, but the more you split your projects into smaller units, the more bugs occur when you mix the units. Sure, you can get your precious fast test runs (and a nice green test), but in reality you're only testing a single unit of a complected app.
EDIT: This reminds my of Rick Hickey's quote from keynote at RailsConf2012:
""We can make the same exact software we are making today with dramatically simpler stuff—dramatically simpler languages, tools, techniques, approaches. Like really radically simpler—radically simpler than Ruby which seems simple.""