What I learned building an app in Hanami A lightweight alternative to Rails

For the past year, I've been loosely following the progress on Hanami (formerly Lotus), a new web framework for Ruby created by Luca Guidi (@jodosha). I recently decided to build a small app in Hanami to get a feel for its design and to understand better its fresh perspective on web development in Ruby. In other words, to answer for myself, "Is Hanami better than Rails?"

The app is a simple integration between GitHub issues and the helpdesk platform, Groove. Visitors can login via OAuth through their GitHub accounts, connect to a Groove account with an API key, import their Groove tickets, and create GitHub issues from these tickets through the app. You can see the source on Github and play with the app hosted on Heroku, where it would help to have accounts on both GitHub and Groove to see how it works.

I've made note of what I learned and some of the challenges I faced while going beyond the getting started guides to build and deploy the app. This post is not an introduction to Hanami - the guides serve as an excellent overview.

The Github-Groove app is built on hanami-0.7.0 . As the framework is under heavy development (as of this writing the latest version is v0.7.2 ), your experience getting started with Hanami may differ.

Hanami opinions are not Rails opinions

Hanami has a lot in common with Rails. Both are web frameworks built on Ruby that employ some version of the Model-View-Controller pattern and, among other things, value convention over configuration. Both frameworks are opinionated about how web apps should be built. In a nutshell, Hanami takes what it likes from Rails and draws the line on certain principles including avoidance of monkey-patching, enforcing modularity, and encouraging the use of "plain old Ruby objects".

If you're coming from Rails, you can expect to learn some new conventions in Hanami. As the guides warn,

learning these conventions may be hard: without change, there is no challenge

The framework pushes you toward "monolith first" while emphasizing "separation of concerns". There are suggestions in the generated directory structure like how the app/ folder is named apps/ in Hanami encouraging you from the start to define sub-applications boundaries under one umbrella, or "container" in Hanami parlance. So while in Rails has engines as an opt-in feature, you build everything as an engine in Hanami. Each "app" gets its own set of views, controllers, assets, configuration, etc. Shared resources, like models, tend to go in lib/ .

You also get useful development tools like generators, migrations, and asset pipelines in Hanami, but expect less ceremony here. Migrations handed off to the venerable Sequel project and the asset story is still young but passable; you won't be able to take advantage of the multitude of Rails-asset gems.

I'd be interested to see Hanami go in a different direction here, like taking advantage of the "frontend explosion" by providing integration with external pipelines as the static-site generator middleman has done or what Shakacode is trying with webpack in react_on_rails .

It's worth noting that Hanami comes with security features baked in for as one would expect, including CSRF protection and app-level secure-by-default options for items like Content Security Policy and X-Frame-Options .

One gotcha is that Hanami does not itself provide any mechanism for code reloading (at the moment). This was not obvious to me starting off since the development server does "appear" to reload code. It turns out that the dev server launches with Shotgun (commonly used in Sinatra projects), to serve each development request in a new process with fork(2) . I didn't pick up on this until several iterations in when I added the SuckerPunch gem and couldn't figure out why my background jobs wouldn't run in development. I added a sync action that allows users to trigger a background job to import ticket data from Groove into the application. Long story short, kicking off background jobs in threads in the request process, as is possible with SuckerPunch, won't work without disabling Shotgun.

Hanami MVC is not Rails MVC

With the Model-View-Controller paradigm, you'll see some big departures from Rails. First, controllers are not classes with "RESTful" methods, but directories of related action classes. In other words, instead of defining #index , #show , #create , etc. in a PostsController , you create a separate class for each action using a mixin that live in a directory that would represent a single controller in Rails.

In my Github-Groove app, here's how I organize the tickets controller:

app/ web/ assets/ config/ controllers/ tickets/ index.rb show.rb sync.rb templates/ views/ ...

Each "action" is a Rack-inspired class whose contract is only that it responds to #call . You still get familiar macros like before filters, but there are new ideas too, like declaring what instance variables are available to the view with expose , inserting action-specific middleware, and whitelisting params at the class level, all of which I find to be huge improvements over the Rails controller design.

module Web::Controllers::Project class Create include Web::Action expose :project before :authenticate! params do param :project do param :groove_access_token, presence: true param :github_repository, presence: true end end def call(params) if params.valid? @project = ProjectRepository.find_or_create_by_params(params[:project]) UserRepository.update_user_project(current_user, @project) flash[:notice] = "Your project has been saved!" redirect_to "/project" end end end end

Arguably, the biggest efforts in Hanami appear to be at this action layer and it shows in the guides and the README where you can find a ton of great information for customizing these classes.

Another big benefit in the controller design, and for most of the Hanami framework, is that unit-testing has a much lower barrier to entry. To get controller tests to work in Rails requires a ton of setup behind the scenes to the point where you essentially have integration tests. Controllers tests in Hanami are much simpler by the simple fact that getting a testable object is as easy as instantiating a Hanami action.

In Hanami, "views" are classes that act more like presenter to represent a model or collection of models for the "templates", which the place of the views/ folder in Rails. Like Rails, file-naming conventions link an action, view, and template. The helper method story is still developing, but you can expect to find some surprises in the docs, like the criticism of Rails monkey-patching of ERB to achieve block-style helpers for things like forms. Expect to get tripped up by these differences in helper syntax which ironically are valid ERB. Hanami does support all the other popular templating engines through Tilt for your preference.

Hanami also provides hanami-model for the model layer as a soft-dependency so you can bring your own ORM if desired. If you choose to use hanami-model as I did, you can expect to leave your ActiveRecord convenience (and baggage) behind. Hanami's model layer emulates the repository pattern where database queries, table mapping, and entities are all separate concerns.

Repositories become a collection of query methods:

class ProjectRepository include Hanami::Repository def self.find_or_create_by_params(params) found = find_by_groove_access_token(params[:groove_access_token]) if found found.update(params) update found else create(Project.new(params)) end end def self.find_by_groove_access_token(groove_access_token) query do where(groove_access_token: groove_access_token) end.first end end

Entities feel basically like POROS that provide a thin layer over attributes. Don't expect to find any database access, validations (by default anyhow), or callbacks here.

class Project include Hanami::Entity attributes :groove_access_token, :github_repository, :syncing def ready? groove_access_token.present? && github_repository.present? end # ... end

Validations do exist in Hanami as a separate mixin but these are more typically done in the params macro at the action-layer.

Expect to write code

While Hanami has its own variety of "magic" of the kind that developers have come to either love or hate in Rails, you can expect to write code you might not otherwise have to in Rails. The framework is still young, so there are missing features. What's not always clear is whether these features have been left out by priority or choice. To figure that out takes some digging on GitHub issues, the Hanami chat and Discourse forum.

Though its database layer has the Sequel library as a foundation, I didn't find the repository and entity functionality as fully-developed. I found myself writing a lot of boilerplate code in the entities and repositories with a lot of co-dependence between the classes. With some more thoughtful design and refactoring, I could probably address this issue, but at this stage, the separation of concerns is less apparent: entities and repositories appear to be tightly bound. Convenience methods are still in the works.

For one, associations are still in development at the time of this writing (see open issue here). Much of my entity code was to fill this gap - to load objects linked by foreign keys via repositories like below.

class Project include Hanami::Entity def tickets(params = {}) TicketRepository.all_by_project(self, params) end end class TicketRepository include Hanami::Repository def self.all_by_project(project, _params = {}) query do where(project_id: project.id).desc(:number) end.all end # ... end

I'm not sure if this is the "Hanami-way", but I found myself doing this kind of thing a lot.

I also ran into some unexpected issues while deploying the application to Heroku where its HANAMI_ENV is set to 'production' . In many cases, custom classes I extracted, like one for sharing a pagination query and another for wrapping the Groove API Ruby Client (my fork with paginated enumeration) weren't "autoloaded" when booting the Hanami application. To resolve this, I added explicit requires like require_relative './pagination' . Again, I didn't have time to dig into whether this issue would be expected or not; I could have been missing something important here.

The Community is still young

That brings me to the community - it's extremely supportive, but still very small. I encountered a lot of helpful folks on chat including @jodosha himself, but there simply hasn't been enough traction to reach StackOverflow critical mass where just about any question you can think of in Rails already has an answer.

This means a lot more code-spelunking in the hanami repositories. To that end, I found the code extremely clean, well-documented, and approachable whereas, even today, I need to brace myself before diving into Rails source.

That said, you can expect to run into edge cases and bugs occasionally that may not yet have a solution, including this incredibly irksome issue that prevents you from accessing the pry console when using binding.pry in Hanami controllers and the problem I mentioned earlier that prevents you from using SuckerPunch in development with Shotgun enabled.

Another challenge is that all those Rails-specific plugins and engines you've come to rely on won't work in Hanami: Yikes, you have build authentication without Devise! Using Warden , the general Rack-based authentication middleware on which Devise is based, is very feasible and you can always rely on OmniAuth like I did.

The lesson here is that with Hanami, you're much more likely to have to "roll up your sleeves" to get to the bottom of issues, figure how to do things that aren't covered by the guides, or otherwise, get from a Rails-specific gem.

Hanami is and is not Rails

So should you build your next app in Hanami? Only you can answer that of course. The lightweight approach in Hanami means there is less to wrap your head around if you're coming from Rails, but there is still a learning curve nonetheless. I'd say it's a worthwhile endeavor to build something small like I did at first to push the boundaries and answer the questions you have about Hanami for yourself.

Hanami treads the same ground as Rails and aims to do a lot of the low level work for you so can focus on what's important - your business logic. Personally, I found a lot of advantages in the "Hanami way" and enjoyed the experience of the new paradigm. My "Rails muscle memory" tripped me up on occasion and left me pining for features that don't exist or are not as well-developed in Hanami yet. I see a lot of potential in the Hanami framework and see it growing into a viable alternative to Rails in the near future.

Check out the GitHub-Groove source and demo app and let me know what I could have done differently.