[rubyist5eva]

I've been doing Rails development for a decade. Concerns are probably the biggest code smell/anti-pattern I've ever seen in any application. It's used as a bandaid to "break up" classes which do too much (but you really don't, you're just hiding the complexity), or it's way over done and everything is magic and almost incomprehensible and unmaintainable. Overall, just a total nightmare to deal with. Would not recommend, and I always try to steer people away from using concers during code reviews.

[Axsuul]

What's the alternative to sharing logic across ActiveRecord models?

[Fire-Dragon-DoL]

Don't put the logic in activerecord models at all. Not even the data. Use activerecord uniquely as a querying mechanism (read or write), don't use relationships and don't put validations in there.

Create objects (aka behavioral objects, aka servoce objects) for the logic and create entities (plain ruby objects) when you need to pass around the data.

Yes, you are essentially eliminating the entirety of activerecord.

After 10 years of rails, you realize that is the only safe way to use that library.

By the way

User User::SignUp Are related. The behavior doesn't need to be in the same object, the namespace takes care of that already.

[e12e]

> Use activerecord uniquely as a querying mechanism (read or write), don't use relationships and don't put validations in there.

I'm sorry, but without relationships - why even use AR for querying? And how? Via connection.select/execute?

[Fire-Dragon-DoL]

It's hard to answer, in the sense that yes, you can use ActiveRecord relationships for the purpose of _building a query_. The point is, you should use them only for that. And it comes with the downsides of distancing you from SQL, which is not negligible.

The problem is if you try to access relationships that you didn't load from the object, that shouldn't be done. It's the autoloading from the database that is the real problem.

If you have enough discipline and enough authority to ensure that never happens within the software you are working on, you can.

It's really culture problem. As soon as you pass around a `user`, someone will type `.posts` on it, or `.save`, suddenly your business logic depends on the database shape, rather than on contracts. What if your database shape is wrong? What if your database shape needs to change?

The goal of good architecture is to be resilient to change, or to even _postpone the choice_ to a moment in time where you have more data to make the right one.

The safest way is: query with activerecord, map to plain ruby objects and discard the activerecord ones immediately.

This will also help you discover the entities you didn't know about, for example, if you have a table of users identified by email, that's the "User" table in Rails. However, let's say that you take only a subset of that table (with select), such as "Full Name" and "Email": this could represent something different. A Newsletter::Subscriber for example.

And the newsletter subscriber entity can be used in the Newsletter::Weekly::Send object, as well as the Newsletter::Unsubscribe. If you realize that this should not have been in the users table in the first place (I have no idea myself), the cost of change is way lower than if you passed an activerecord object around.

I hope this answers some of your questions. There is a lot to say on the topic. I'm happy to chat more on slack or an online videoconference session

[e12e]

Thank you for taking the time to answer, and also to amw-zero below.

I think I understand more of the sentiment now.

> As soon as you pass around a `user`, someone will type `.posts` on it, or `.save`

I'm not much of a fan of the active record pattern, and I can see (have seen) how optimistic/naive developers can get in trouble - but I feel these are two separate problems:

> someone will type `.posts` on it

This doesn't have to be all bad, just make sure there was a join or include first - perhaps via a scope (eg: User.with_posts).

I suppose some rails apps end up doing "much more than crud", and then it can be easy to stumble. But I find that with some modicum of discipline, "fat models" can go a long way towards making "slim controllers" fall out naturally.

> someone will type.. `.save`, on it

This why I use AR objects, so I can do crud. Sure if dealing with "posts" (plural) you want to avoid: posts.map... save in favour of update_all.

And while there's save! - data integrity belongs in db constraints. But validations are a great tool for better ux and error feedback. The major problem today, is probably that you'd want to (only) run them as client side js.

[Fire-Dragon-DoL]

I did delete this post, I'm not sure how it came back. I wasn't happy with my answer.

I would avoid any logic in the models, they already have 3 responsibilities (data gateway, data holder and validation).

For CRUD apps, Rails has competitors that can't be overlooked, there are alternatives: PostgREST, Hasura + Forst Admin provide full crud UI with borderline no code.

In all honesty, you don't have to look far. Elixir + Phoenix, which is not free of mistakes, manages to be a better Rails than Rails itself. The validation is isolated, the database access is isolated from the model, no autoloading is involved.

[geospeck]

That is very interesting approach! I’ve never worked on a project that doesn’t use AR relationships e.g has_many... at all.

Do you have an example app or a blog post exposing this pattern? It would be very interesting to see how this actually works. Thanks you very much for bringing this up!

[amw-zero]

They aren’t saying to not use has_many. They’re saying to not use the association method that gets put on the AR object from has_many. For example, if a User has_many Posts, they’re saying to avoid calling user.posts.

That may seem weird, but the association still has value: for querying. You can still write: User.joins(:posts) for example.

The problem with the association methods is that they aren’t really methods because they always execute a query. A lot of longtime Rails developers get tired of the database being involved in every step of the way in a request, because it leads to a lack of separation of concerns.

[Fire-Dragon-DoL]

Unfortunately I don't. I work less and less on the CRUD part of the apps, however as I recommended in another comment, Phoenix (Elixir's alternative to Rails) does that correctly: associations are used for the purpose of querying, not as methods. In combination with isolated validations and the data gateway isolated, it's easy to achieve separation of concerns and have a more maintainable code-base.

[jaxn]

I am constantly guarding against AR callbacks as well as the insane number of queries that come from lazy loading relationships.

Might have to explore your suggestions a bit.

[Fire-Dragon-DoL]

Good idea. The lazy loading has been particularly bad in the code-base I worked on recently, to the point that pieces of code thought to be entirely isolated from the database were actually accessing the entirety of it.

Callbacks to me are just an indicator of what is missing, an object that encapsulates the "user case". There is a need to do "other things once the data is written", but that is specific to the location where the writing is happening. Modifying a post content from an administrator's perspective could trigger an email to inform the user "your post has been moderated", but the user modifying it's own post shouldn't. Yes you can have callbacks with IFs, but the use-cases will keep piling up. Now you have a rake task that fixes some posts' content due to a bug in the whatever part of the code parsed the text. It shouldnt' trigger the email, but you do have a callback in there.

[megraf]

You're correct on all fronts. Domain driven design, POROs- all of it. I bet you maintain something nice!

[Fire-Dragon-DoL]

Thanks, I really appreciate that.

I do my best, but the sad reality is that I made an insanely large amount of mistakes in my development life, I didn't reach these conclusions without doing damage myself.

I try to give back by training developers and making sure the business gain awareness so they don't have to experience the complete halt of feature development when the software becomes unsuited for changes.

[joelbluminator]

Not arguing your points, just a wondering: Why stick to Rails then? Without ActiveRecord Rails is a pretty big bloat with a mediocre view layer. Routing is nice but I'm sure Sinatra could do that as well.

[Fire-Dragon-DoL]

The majority of Ruby jobs is on Rails. All I need, personally, is a server like Puma, a router like Roda and the pg gem really. Then of course it depends on the application you need to develop.

I would probably need some library to coerce string values to types (boolean, integer) for forms, and a mapping mechanism of some form to convert a pg result in a data shape I control.

[jjgreen]

So why use AR? Sequel is a thing.

[swader999]

That's a breath of fresh air to read.

[dasil003]

If you are truly sharing logic then it might be okay, but typically I've seen concerns added as a way to organize code when ActiveRecord models get too big. At this point a lot of people reach for Concerns because it is right there in Rails waiting to be used, but ultimately it's just papering over the problem of bloated classes with too many responsibilities. I usually prefer to add some kind of service layer to handle complex manipulation and object lifecycle so that ActiveRecord just manages querying/persistence with most if not all business logic at a higher layer.

[xipho]

> it's just papering over the problem of bloated classes with too many responsibilities.

If you're blindly coding away and using some feature just because it's there you've got bigger problems with how you go about programming, that's not special to Rails.

I find concerns to be an intermediate mechanism to use in migrating the bloat out to some other abstract level. However, adding abstractions beyond MCV has it's own problems, each level means the developer has to understanding something more, one can't escape that.

Pretending that one can fully anticipate the complexity of large project and model it perfectly via the way you organize your code is really only something done by the the beginning programmer. Concerns can be very tight, as you note, and of course any feature can be used poorly. I like concerns, we have many that haven't been touched, and lead to an ability to extremely rapidly spread functionality around a huge number of models (e.g. different annotation classes). I'm also guilty of using them in the intermediate manner above. In the long term, one sees these patterns, and doesn't fret about such things.

[seancoleman]

I think a different way of looking at the problem is that ActiveRecord models really shouldn’t have much, if any logic. Instead, logic should get delegated to other types of object, such as services, decorators, query objects, etc. While “fat models” is certainly better than “fat controllers”, I’m afraid it lead the Rails community astray with large-scale apps that required more nuanced architecture.

[tomc1985]

Agreed. Concerns break large classes up to an innumerable amount of small files. It becomes so hard to keep track of simple interactions because they are spread across half a dozen files and/or contexts.

[welearnednothng]

I empathize with everything you're saying here, but I do humbly disagree. I've experienced exactly what you're talking about, and it's a nightmare. Frankly, I think the Rails codebase itself even suffers from an over use of concerns that can make figuring out where functionality comes from very frustrating at times.

That said, concerns are mixins, and mixins are, in the simplest of terms, more or less multiple inheritance. That's powerful stuff, and powerful stuff in the wrong hands (which includes every hand that'll touch it, not just the author!) will always get you in trouble. That could be the motto for Rails itself - powerful stuff, but in the wrong hands it'll get you into trouble!

My first exposure to concerns in Rails was a awful codebase for a well known company with massive classes that someone went on a weekend bender and shrunk down to less massive classes by introducing dozens of concerns. It made the classes _appear_ smaller, but they weren't actually. In reality, it was just hiding away much of the complexity and horrible decision making that made the code so hard to reason about and maintain and took things from bad to worse as a result.

That said, when you have a well architected code base to begin with (as in before you start introducing concerns) that has svelte classes with appropriate responsibilities, with shared logic broken out into "services" or whatnot, concerns can be a really nice way to share isolated functionality that can lead to cleaner classes without obfuscating what's going on. Quite the opposite - used well, they can tuck away (but not altogether hide) ancillary functionality allowing the meat of a method to be highlighted instead of drowned out by pre- and post-requisite behavior that might take up more LoC than the unique business logic of a given controller action thus obfuscating the functionality specific to that method.

On my current and previous project, concerns worked out great for the teams (which included junior devs) but were used sparingly and typically introduced by experienced devs. Also, taking a quick glance, it seems like Controller concerns are favored far more, and often involve calls to class-level ActionController methods such as rescue_from, overriding protect_from_forgery defaults, settings layouts, before_action, helper_method, etc. - things that you can't just tuck into a service class or method that gets called from the controller and would otherwise require someone remembering the correct combinations of code to sprinkle into a controller or creating a controller to inherit from (which isn't practically different from concerns but can paint you into a corner). They're also never used for the business logic of an action, only supporting functionality (again, pre- and post- requisite functionality or introducing class-level helper methods that can be reused).

All that being said, for a team that isn't confident in how to use concerns effectively, I'd also steer them away and guide them to consider alternative approaches. But at face value, I don't consider concerns an anti-pattern and have found that, when used appropriately, they can be a great tool in maintaining a clean codebase.