5 ms·

The problem with controllers

52 points by karmajunkie 15y ago

ecoffey 15y ago
This is a good read, and something I agree with. The command pattern that you're showing here almost feels like the "write" inverse to the Presenter "read" action. The way I've been thinking about it for myself is to imagine your Domain Objects as this 3D space of object relationships and interactions. So a Presenter cuts a 2D plane through that space and let's you view from a certain perspective. In the case of Commands, you're taking a certain perspective and mutating that 3D space through it. Not sure if that helps anyone else :-) Also the focused_controller project looks really interesting as well. I was working on my own web framework, that made Actions first class objects as well. And since it was built on this slick IoC library, your Actions could just declare they need this Command, or these two Services to complete the request and they would automagically get them. I really like the idea of "one object(graph) to represent accomplishing a task", and then just having that object(graph) go do the work.
papsosouid 15y ago
The issue of model code creeping into controllers is common with rails and rails-style frameworks precisely because they are not MVC frameworks. MVC was a pattern created for making GUI apps in smalltalk in the 70s/80s. It has gradually been warped and twisted since then, especially when people tried to cludge it onto web development. The resulting thing doesn't really resemble MVC at all, and certainly doesn't deliver the benefits MVC was created to deliver. MVC is a triangle, rails style frameworks are a line. This is called MVA (Model-View-Adapter). The "adapter" being in between the view and the model who can only interact with the adapter and not each other. The second issue is that in adapting MVC to the web, many frameworks continued with the "one controller per view" notion, despite that being done because of the limitations imposed when creating GUI apps. There is no need for multiple controllers in a web app, all input comes in the same way no matter what view the user is seeing. In fact, the user doesn't even need to be seeing a view, there is nothing tying a view to what actions are possible, you can always submit any http request you want. Your "routes" are your controller, there is no need for a second level of controllers on top of that. The goal of MVC was to expose model functionality to the user directly so they could understand and work with the domain model clearly and easily. Controller meant "controls the input and output" not "controls the users experience". The guy who created MVC considers naked objects style frameworks to be the closest thing to MVC for the web, not rails style MVA frameworks. And there is something very weird about this statement: >On top of that, it’s very common to see logic pushed down into the model Of course that is common, that is what is supposed to happen. Models are not "stupid containers to pretend to kinda represent my DB sorta but not really". Models are the business logic. Models are the actual application. You are modelling the domain, not modelling the database. The model is the domain, it is all the business logic. The view is the way we present information to the user. The controller is the part that handles input and output. Very simple and effective system, but very poorly understood and virtually never used any more.
- karmajunkie 15y ago
  The problem with "logic getting pushed down into the model" and the gist of the statement is that not all logic is domain logic. Reaching out and touching facebook for a status update, for example, is not domain logic and doesn't belong in a model. And while I agree that we should be modeling the domain, not the database, I think its clear from working on a lot of complex and legacy applications over the last several years rails developers model what the database allows, not the actual domain, thanks to the widespread acceptance of ActiveRecord as the only tool in that toolchest. I'm in 100% agreement WRT to MVC—Rails' idea of MVC was never really MVC as MVC was originally envisioned.
  - papsosouid 15y ago
    I don't understand the distinction of "not domain logic". If your application requirements are "when user does X, update facebook" then that is clearly part of the domain and should absolutely be in the models.
    - karmajunkie 15y ago
      Oh, i disagree with that completely. A user having a status is domain logic. Pulling that status from an external dependency is decidedly not.
      - endersshadow 15y ago
        How is it not? What draws the line between domain logic and non-domain logic? It would seem to me that, by definition, anything your application does would fall into that application's domain, right? What other domain would it be in? Where would you put a request to a third party for supplemental data, if not in the models?
        karmajunkie 15y ago
        If it were part of your domain, it'd be part of your application. Connection to facebook by definition is outside the scope of your domain. You can take a couple of different strategies to it, but in general the best way to handle that is to introduce a class whose responsibility is to connect to facebook and return a status (generally speaking, a Service) and something like a Command or Job that accesses the FacebookService and updates your user model. Part of the problem with speaking about domains here (aside from being nonspecific about something that is by its very nature quite specific) is that Rails has an extraordinariliy half-assed approach to domain oriented design (I don't want to use 'DDD' here just to avoid buzzwords). Developers have been told for years to just push it into the model because all the work belongs there, but that's BS. a LOT of the work has no business being there.
PaulHoule 15y ago
Kinda funny, I settled in on a "command" architecture for PHP apps around 2001 because the ORM kind of model always has some big semantic gap in it.
Stwerner 15y ago
Slightly off-topic, but does anyone have any resources for learning more about these and other design patterns that show up on HN from time to time?
- karmajunkie 15y ago
  Design Patterns in Ruby would probably be a good place to start, then the original GoF Design Patterns book, along with Enterprise Design Patterns which came later. Also check out the DDD/CQRS google group: http://groups.google.com/group/dddcqrs http://groups.google.com/group/dddcqrs
  - Stwerner 15y ago
    Thank you! I had seen the Design Patterns in Ruby book when I looked around on Amazon, but wasn't sure if it would be a good choice. Ordered now, though.
kastephens 14y ago
The problem isn't controllers. Controller are responsible for mediating the behavior presented to external actors, not defining complex "business" logic. Complex logic interacts with complex object graphs, not individual models. Therefore, complex logic does not belong in models or controllers (or views). Complex logic belongs in instantated objects (not modules) that represent complex logic. This style may also be known as the "Strategy" Design Pattern. Strategy objects can have state during their activities, this is why they should be instantiated. Strategy objects simplify testing because they can be connected with any object graph that presents the same interfaces as the target object graphs. This leads to interchangable Strategy objects that represent generic behavior which can be applied to actual, simulated or speculative object graphs.

52 points by karmajunkie 15y ago

This is a good read, and something I agree with. The command pattern that you're showing here almost feels like the "write" inverse to the Presenter "read" action. The way I've been thinking about it for myself is to imagine your Domain Objects as this 3D space of object relationships and interactions. So a Presenter cuts a 2D plane through that space and let's you view from a certain perspective. In the case of Commands, you're taking a certain perspective and mutating that 3D space through it. Not sure if that helps anyone else :-) Also the focused_controller project looks really interesting as well. I was working on my own web framework, that made Actions first class objects as well. And since it was built on this slick IoC library, your Actions could just declare they need this Command, or these two Services to complete the request and they would automagically get them. I really like the idea of "one object(graph) to represent accomplishing a task", and then just having that object(graph) go do the work.

papsosouid 15y ago

The issue of model code creeping into controllers is common with rails and rails-style frameworks precisely because they are not MVC frameworks. MVC was a pattern created for making GUI apps in smalltalk in the 70s/80s. It has gradually been warped and twisted since then, especially when people tried to cludge it onto web development. The resulting thing doesn't really resemble MVC at all, and certainly doesn't deliver the benefits MVC was created to deliver. MVC is a triangle, rails style frameworks are a line. This is called MVA (Model-View-Adapter). The "adapter" being in between the view and the model who can only interact with the adapter and not each other. The second issue is that in adapting MVC to the web, many frameworks continued with the "one controller per view" notion, despite that being done because of the limitations imposed when creating GUI apps. There is no need for multiple controllers in a web app, all input comes in the same way no matter what view the user is seeing. In fact, the user doesn't even need to be seeing a view, there is nothing tying a view to what actions are possible, you can always submit any http request you want. Your "routes" are your controller, there is no need for a second level of controllers on top of that. The goal of MVC was to expose model functionality to the user directly so they could understand and work with the domain model clearly and easily. Controller meant "controls the input and output" not "controls the users experience". The guy who created MVC considers naked objects style frameworks to be the closest thing to MVC for the web, not rails style MVA frameworks. And there is something very weird about this statement: >On top of that, it’s very common to see logic pushed down into the model Of course that is common, that is what is supposed to happen. Models are not "stupid containers to pretend to kinda represent my DB sorta but not really". Models are the business logic. Models are the actual application. You are modelling the domain, not modelling the database. The model is the domain, it is all the business logic. The view is the way we present information to the user. The controller is the part that handles input and output. Very simple and effective system, but very poorly understood and virtually never used any more.

karmajunkie 15y ago
The problem with "logic getting pushed down into the model" and the gist of the statement is that not all logic is domain logic. Reaching out and touching facebook for a status update, for example, is not domain logic and doesn't belong in a model. And while I agree that we should be modeling the domain, not the database, I think its clear from working on a lot of complex and legacy applications over the last several years rails developers model what the database allows, not the actual domain, thanks to the widespread acceptance of ActiveRecord as the only tool in that toolchest. I'm in 100% agreement WRT to MVC—Rails' idea of MVC was never really MVC as MVC was originally envisioned.
- papsosouid 15y ago
  I don't understand the distinction of "not domain logic". If your application requirements are "when user does X, update facebook" then that is clearly part of the domain and should absolutely be in the models.
  - karmajunkie 15y ago
    Oh, i disagree with that completely. A user having a status is domain logic. Pulling that status from an external dependency is decidedly not.
    - endersshadow 15y ago
      How is it not? What draws the line between domain logic and non-domain logic? It would seem to me that, by definition, anything your application does would fall into that application's domain, right? What other domain would it be in? Where would you put a request to a third party for supplemental data, if not in the models?
      - karmajunkie 15y ago
        If it were part of your domain, it'd be part of your application. Connection to facebook by definition is outside the scope of your domain. You can take a couple of different strategies to it, but in general the best way to handle that is to introduce a class whose responsibility is to connect to facebook and return a status (generally speaking, a Service) and something like a Command or Job that accesses the FacebookService and updates your user model. Part of the problem with speaking about domains here (aside from being nonspecific about something that is by its very nature quite specific) is that Rails has an extraordinariliy half-assed approach to domain oriented design (I don't want to use 'DDD' here just to avoid buzzwords). Developers have been told for years to just push it into the model because all the work belongs there, but that's BS. a LOT of the work has no business being there.

PaulHoule 15y ago

Kinda funny, I settled in on a "command" architecture for PHP apps around 2001 because the ORM kind of model always has some big semantic gap in it.

Stwerner 15y ago

Slightly off-topic, but does anyone have any resources for learning more about these and other design patterns that show up on HN from time to time?

karmajunkie 15y ago
Design Patterns in Ruby would probably be a good place to start, then the original GoF Design Patterns book, along with Enterprise Design Patterns which came later. Also check out the DDD/CQRS google group: http://groups.google.com/group/dddcqrs http://groups.google.com/group/dddcqrs
- Stwerner 15y ago
  Thank you! I had seen the Design Patterns in Ruby book when I looked around on Amazon, but wasn't sure if it would be a good choice. Ordered now, though.

kastephens 14y ago

The problem isn't controllers. Controller are responsible for mediating the behavior presented to external actors, not defining complex "business" logic. Complex logic interacts with complex object graphs, not individual models. Therefore, complex logic does not belong in models or controllers (or views). Complex logic belongs in instantated objects (not modules) that represent complex logic. This style may also be known as the "Strategy" Design Pattern. Strategy objects can have state during their activities, this is why they should be instantiated. Strategy objects simplify testing because they can be connected with any object graph that presents the same interfaces as the target object graphs. This leads to interchangable Strategy objects that represent generic behavior which can be applied to actual, simulated or speculative object graphs.