Oprah

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Opinionated presenters for Rails 5 - without the cruft.

Table of Contents

Overview

If you’ve ever worked on a sufficiently large Rails application you’ve probably experienced the Rails helper mess first hand. Helper methods are annoying to locate, hard to test and not terribly expressive.

So why another presenter/decorator library? Oprah was written with a few simple goals in mind only covered partially (or not at all) by other gems:

  • Lightweight
  • Presenters should be easy to test
  • Avoid monkey patching, where possible :monkey::gun:
  • Embrace convention over configuration
  • First-class support for composition (modules and concerns)

Installation

Add this line to your application’s Gemfile:

ruby gem 'oprah'

And then execute:

$ bundle

Getting started

Oprah expects a single presenter for each of your classes or modules. If your model is called User it will look for a class called UserPresenter:

``` ruby class User def first_name “John” end

def last_name “Doe” end end

class UserPresenter < Oprah::Presenter def name “#first_name #last_name” end end ```

Oprah will figure out the presenters by itself so you don’t have to instantiate your presenter classes directly:

``` ruby presenter = Oprah.present(User.new)

presenter.name # => “John Doe”

```

Of course, all the regular methods on your model are still accessible:

ruby presenter.first_name # => "John"

If you DO want to use a specific presenter, you can simply instantiate it yourself:

ruby SomeOtherPresenter.new(User.new)

ActionController integration

Now, where do we put our presenters? Ideally, you’d want to expose them in your controller. Oprah avoids monkey patching and generally it’s good to be aware of what’s going on, even if that means to be (at least a little bit) explicit.

Here’s how you can use Oprah presenters from your controller:

ruby class UsersController < ApplicationController def show @user = present User.find(params[:id]) end end

This will also take care of passing the correct view context to the presenter, which you can access with the #view_context (or shorter, #h) instance method.

Collections

Oprah has basic support for collections with .present_many. It will simply apply it’s .present behavior to each object in the given collection:

``` ruby users = [User.new, User.new] presenters = Oprah.present_many(users)

presenters.first.kind_of?(UserPresenter) # => true

presenters.last.kind_of?(UserPresenter) # => true ```

Of course, this works in controllers, too:

ruby class UserController < ApplicationController def index @users = present_many User.all end end

Associations

You can also automatically use presenters for your associations using the #presents_one and #presents_many macros. Let’s say you have the following Project model:

ruby class Project has_many :users has_one :owner, class_name: "User" end

Oprah lets you easily wrap the associated objects:

ruby class ProjectPresenter < Oprah::Presenter presents_many :users presents_one :owner end

Note that you don’t need to explicitly state the association class.

Composition

Let’s say you extraced some behaviour out of your model into a reusable module (or ActiveSupport::Concern). Oprah lets you write a single, separate presenter for this module and automatically chains it to your “main presenter” by walking up the ancestor chain of the given object.

Let’s say we want to mix a shared Describable module into our User class from above and render the description to HTML:

``` ruby module Describable def description “AWESOME” end end

class User include Describable end

class DescribablePresenter < Oprah::Presenter def description Kramdown::Document.new(object.description).to_html end end ```

You can now access the methods of both, UserPresenter and DescribablePresenter:

``` ruby presenter = Oprah.present(User.new)

presenter.description => “<p>AWESOME</p>\n”

presenter.name # => John Doe ```

Performance

Of course, looking up all the presenters would imply a performance issue. But don’t worry, Oprah caches all matching presenters for a class (and busts it’s cache on code reloads for a smooth development experience).

Ordering

Oprah walks your object’s ancestor chain in reverse. For example, you’d be able to access the methods exposed by the DescribablePresenter from your UserPresenter. You can even use super:

``` ruby class DescribablePresenter < Oprah::Presenter def baz “foo” end end

class UserPresenter < Oprah::Presenter def baz super + “bar” end end

Oprah.present(User.new).baz # => “foobar” ```

Choosing presenters

When presenting an object you can optionally choose which presenter classes to use:

ruby Oprah.present(User.new, only: DescribablePresenter)

This parameter takes either a single presenter or an Array of presenters. The presenter(s) given need to match the object’s class or one of it’s ancestors. Non-matching presenters given will be ignored.

License

Released under the MIT license. See the LICENSE file for details.

Author

Tobias Svensson, @endofunky, http://github.com/endofunky