Trailblazer

Trailblazer is a thin layer on top of Rails. It gently enforces encapsulation, an intuitive code structure and gives you an object-oriented architecture.

In a nutshell: Trailblazer makes you write logicless models that purely act as data objects, don't contain callbacks, nested attributes, validations or domain logic. It removes bulky controllers and strong_parameters by supplying additional layers to hold that code and completely replaces helpers.

Please buy my book Trailblazer - A new architecture for Rails and let me know what you think! I am still working on the book but keep adding new chapters every other week. It will be about 300 pages and we're developing a real, full-blown Rails/Trb application.

The demo application implements what we discuss in the book.

Mission

While Trailblazer offers you abstraction layers for all aspects of Ruby On Rails, it does not missionize you. Wherever you want, you may fall back to the "Rails Way" with fat models, monolithic controllers, global helpers, etc. This is not a bad thing, but allows you to step-wise introduce Trailblazer's encapsulation in your app without having to rewrite it.

Trailblazer is all about structure. It helps re-organize existing code into smaller components where different concerns are handled in separated classes. Forms go into form objects, views are object-oriented MVC controllers, the business logic happens in dedicated domain objects backed by completely decoupled persistence objects.

Again, you can pick which layers you want. Trailblazer doesn't impose technical implementations, it offers mature solutions for recurring problems in all types of Rails applications.

Trailblazer is no "complex web of objects and indirection". It solves many problems that have been around for years with a cleanly layered architecture. Only use what you like. And that's the bottom line.

A Concept-Driven OOP Framework

Trailblazer offers you a new, more intuitive file layout in Rails apps where you structure files by concepts.

app
├── concepts
│   ├── comment
│   │   ├── cell.rb
│   │   ├── views
│   │   │   ├── show.haml
│   │   │   ├── list.haml
│   │   ├── assets
│   │   │   ├── comment.css.sass
│   │   ├── operation.rb
│   │   ├── twin.rb

Files, classes and views that logically belong to one concept are kept in one place. You are free to use additional namespaces within a concept. Trailblazer tries to keep it as simple as possible, though.

Architecture

Trailblazer extends the conventional MVC stack in Rails. Keep in mind that adding layers doesn't necessarily mean adding more code and complexity.

The opposite is the case: Controller, view and model become lean endpoints for HTTP, rendering and persistence. Redundant code gets eliminated by putting very little application code into the right layer.

The Trailblazer stack.

Routing

Trailblazer uses Rails routing to map URLs to controllers (we will add simplifications to routing soon).

Controllers

Controllers are lean endpoints for HTTP. They differentiate between request formats like HTML or JSON and immediately dispatch to an operation. Controllers do not contain any business logic.

Trailblazer provides four methods to present and invoke operations. But before that, you need to include the Controller module.

class CommentsController < ApplicationController
  include Trailblazer::Operation::Controller

Rendering the form object

Operations can populate and present their form object so it can be used with simple_form and other form helpers.


def new
  form Comment::Create
end

This will run the operation but not its validate code. It then sets the @form instance variable in the controller so it can be rendered.

= form_for @form do |f|
  = f.input f.body

#form is meant for HTML actions like #new and #edit, only.

Running an operation

If you do not intend to maintain different request formats, the easiest is to use #run to process incoming data using an operation.

def create
  run Comment::Create
end

This will simply run Comment::Create[params].

You can pass your own params, too.

def create
  run Comment::Create, params.merge({current_user: current_user})
end

An additional block will be executed only if the operation result is valid.

def create
  run Comment::Create do |op|
    return redirect_to(comments_path, notice: op.message)
  end
end

Note that the operation instance is yield to the block.

The case of an invalid response can be handled after the block.

def create
  run Comment::Create do |op|
    # valid code..
    return
  end

  render action: :new
end

Don't forget to return from the valid block, otherwise both the valid block and the invalid calls after it will be invoked.

Responding

Alternatively, you can use Rails' excellent #respond_with to let a responder take care of what to render. Operations can be passed into respond_with. This happens automatically in #respond, the third way to let Trailblazer invoke an operation.

def create
  respond Comment::Create
end

This will simply run the operation and chuck the instance into the responder letting the latter sort out what to render or where to redirect. The operation delegates respective calls to its internal model.

You can also handle different formats in that block. It is totally fine to do that in the controller as this is endpoint logic that is HTTP-specific and not business.

def create
  respond Comment::Create do |op, formats|
    formats.html { redirect_to(op.model, :notice => op.valid? ? "All good!" : "Fail!") }
    formats.json { render nothing: true }
  end
end

The block passed to #respond is always executed, regardless of the operation's validity result. Goal is to let the responder handle the validity of the operation.

The formats object is simply passed on to #respond_with.

Presenting

For #show actions that simply present the model using a HTML page or a JSON or XML document the #present method comes in handy.

def show
  present Comment::Update
end

Again, this will only run the operation's setup and provide the model in @model. You can then use a cell or controller view for HTML to present the model.

For document-based APIs and request types that are not HTTP the operation will be advised to render the JSON or XML document using the operation's representer.

Note that #present will leave rendering up to you - respond_to is not called.

Controller API

In all three cases the following instance variables are assigned: @operation, @form, @model.

Named instance variables can be included, too. This is documented here.

Operation

Operations encapsulate business logic. One operation per high-level domain function is used. Different formats or environments are handled in subclasses. Operations don't know about HTTP.

class Comment < ActiveRecord::Base
  class Create < Trailblazer::Operation
    def process(params)
      # do whatever you feel like.
      self
    end
  end
end

Operations only need to implement #process which receives the params from the caller.

Call style

The simplest way of running an operation is the call style.

op = Comment::Create[params]

Using Operation#[] will return the operation instance. In case of an invalid operation, this will raise an exception.

Note how this can easily be used for test factories.

let(:comment) { Comment::Create[valid_comment_params].model }

Using operations as test factories is a fundamental concept of Trailblazer to remove buggy redundancy in tests and manual factories.

Run style

You can run an operation manually and use the same block semantics as found in the controller.

Comment::Create.run(params) do |op|
  # only run when valid.
end

Of course, this does not throw an exception but simply skips the block when the operation is invalid.

Validations

Operations usually have a form object which is simply a Reform::Form class. All the API documented in Reform can be applied and used.

The operation makes use of the form object using the #validate method.

class Comment < ActiveRecord::Base
  class Create < Trailblazer::Operation
    contract do
      property :body, validates: {presence: true}
    end

    def process(params)
      @model = Comment.new

      validate(params[:comment], @model) do |f|
        f.save
      end
    end
  end
end

The contract (aka form) is defined in the ::contract block. You can implement nested forms, default values, validations, and everything else Reform provides.

In case of a valid form the block for #validate is invoked. It receives the populated form object. You can use the form to save data or write your own logic.

Technically speaking, what really happens in Operation#validate is the following.

contract_class.new(@model).validate(params[:comment])

This is a familiar work-flow from Reform. Validation does not touch the model.

Models

Models for persistence can be implemented using any ORM you fancy, for instance ActiveRecord or Datamapper.

In Trailblazer, models are completely empty and solely configure database-relevant directives and associations. No business logic is allowed in models. Only operations, views and cells can access models directly.

Views

View rendering can happen using the controller as known from Rails. This is absolutely fine for simple views.

More complex UI logic happens in View Models as found in Cells. View models also replace helpers.

  1. HTTP API Consuming and rendering API documents (e.g. JSON or XML) is done via roar and representable. They usually inherit the schema from Contracts .

  2. Tests Subject to tests are mainly Operations and View Models, as they encapsulate endpoint behaviour of your app. As a nice side effect, factories are replaced by simple Operation calls.

Trailblazer is basically a mash-up of mature gems that have been developed over the past 10 years and are used in hundreds and thousands of production apps.

Controller API

Normalizing params

Override #process_params! to add or remove values to params before the operation is run. This is called in #run, #respond and #present.

class CommentsController < ApplicationController
  # ..

private
  def process_params!(params)
    params.merge!(current_user: current_user)
  end
end

This centralizes params normalization and doesn't require you to do that in every action manually.

Different Request Formats

The controller helpers #present and #respond automatically pass the request body into the operation via the params hash. It's up to the operation's builder to decide which class to instantiate.

class Create < Trailblazer::Operation
  builds do |params|
    JSON if params[:format] == "json"
  end
end

[Note that this will soon be provided with a module.]

Operation API

CRUD Semantics

You can make Trailblazer find and create models for you using the CRUD module.

require 'trailblazer/operation/crud'

class Comment < ActiveRecord::Base
  class Create < Trailblazer::Operation
    include CRUD
    model Comment, :create

    contract do
      # ..
    end

    def process(params)
      validate(params[:comment]) do |f|
        f.save
      end
    end
  end
end

You have to tell CRUD the model class and what action to implement using ::model.

Note how you do not have to pass the @model to validate anymore. Also, the @model gets created automatically and is accessable using Operation#model.

In inherited operations, you can override the action, only, using ::action.

class Update < Create
  action :update
end

Another action is :find (which is currently doing the same as :update) to find a model by using params[:id].

Normalizing params

Override #setup_params! to add or remove values to params before the operation is run.

class Create < Trailblazer::Operation
  def process(params)
    params #=> {show_all: true, admin: true, .. }
  end

  private
    def process_params!(params)
      params.merge!(show_all: true) if params[:admin]
    end
  end
end

This centralizes params normalization and doesn't require you to do that manually in #process.

Background Processing

To run an operation in Sidekiq (ActiveJob-support coming!) all you need to do is include the Worker module.

require 'trailblazer/operation/worker'

class Comment::Image::Crop < Trailblazer::Operation
  include Worker

  def process(params)
    # will be run asynchronously.
  end
end

Rendering Operation's Form

You have access to an operation's form using ::present.

Comment::Create.present(params)

This will run the operation's #process method without the validate block and return the contract.

Marking Operation as Invalid

Sometimes you don't need a form object but still want the validity behavior of an operation.

def process(params)
  return invalid! unless params[:id]

  Comment.find(params[:id]).destroy
  self
end

#invalid! returns self per default but accepts any result.

Worker::FileMarshaller: needs representable 2.1.1 (.schema)

Testing Operations

Autoloading

Use our autoloading if you dislike explicit requires.

You can just add

require "trailblazer/autoloading"

to config/initializers/trailblazer.rb and implementation classes like Operation will be automatically loaded.

Operation Autoloading

If you structure your CRUD operations using the app/concepts/*/crud.rb file layout we use in the book, the crud.rb files are not gonna be found by Rails automatically. It is a good idea to enable CRUD autoloading.

At the end of your config/application.rb file, add the following.

require "trailblazer/rails/railtie"

This will go through app/concepts/, find all the crud.rb files, autoload their corresponding namespace (e.g. Thing, which is a model) and then load the crud.rb file.

Undocumented Features

(Please don't read this section!)

Additional Model Setup

Override Operation#setup_model(params) to add nested objects that can be infered from params or are static.

This is called right after #model!.

ActiveModel Semantics

When using Reform::Form::ActiveModel (which is used automatically in a Rails environment to make form builders work) you need to invoke model Comment in the contract. This can be inferred automatically from the operation by including CRUD::ActiveModel.

class Create < Trailblazer::Operation
  include CRUD
  include CRUD::ActiveModel

  model Comment

  contract do # no need to call ::model, here.
    property :text
  end

If you want that in all CRUD operations, check out how you can include it automatically.

Named Controller Instance Variables

If you want to include named instance variables for you views you must include another ActiveRecord specific module.

require 'trailblazer/operation/controller/active_record'

class ApplicationController < ActionController::Base
  include Trailblazer::Operation::Controller
  include Trailblazer::Operation::Controller::ActiveRecord
end

This will setup a named instance variable of your operation's model, for example @song.

Why?

  • Grouping code, views and assets by concepts increases the maintainability of your apps. Developers will find their way faster into your structure as the file layout is more intuitive.
  • Finding bugs gets less frustrating as encapsulated layers allow testing components in total isolation. Once you know your form and your view are ok, it must be the parsing code.
  • The reusability of code increases drastically as Trailblazer gently pushes you towards encapsulation. No more redundant helpers but clean inheritance.
  • No more surprises from ActiveRecord's massive API. The separation between persistence and domain automatically results in smaller, less destructive APIs for your models.