🧙 Magic Presenter
A bit of history: this gem was inspired by digging deeper into Draper with an eye on a refactoring.
Based on Magic Decorator, it implements a presenter logic.
Installation
Install the gem and add to the application's Gemfile by executing:
$ bundle add magic-presenter
If bundler is not being used to manage dependencies, install the gem by executing:
$ gem install magic-presenter
After all the gems are bundle
d run the installer in the project directory to generate the necessary files:
$ bin/rails generate magic:presenter:install
Usage
Magic::Presenter::Base
is a basic presenter class to be inherited by any other presenter.
It further inherits from SimpleDelegator
.
class PersonPresenter < Magic::Presenter::Base
def name = "#{first_name} #{last_name}"
end
class Person
include ActiveModel::Model
attr_accessor :first_name, :last_name
end
person = Person.new(first_name: 'John', last_name: 'Smith').decorate
person.name # => "John Smith"
Magic::Presentable
This module includes Magic::Decoratable
and allows a descendant to be decorated by presenters only.
Presenter class is being inferred automatically.
When no presenter is found,
-
#decorate
returnsnil
, -
#decorate!
raisesMagic::Lookup::Error
, -
#decorated
returns the original object.
Generators
A generator can be used to generate a presenter:
$ bin/rails generate presenter Person
See the help for more info:
$ bin/rails generate presenter --help
View helpers
A presenter can use any helpers via #helpers
(aliased as #h
) both in class and instance methods:
class PersonPresenter < Magic::Presenter::Base
def self.links
[ h.link_to('All', model_class) ]
end
def link(...)
helpers.link_to(name, self, ...)
end
end
A view context must be set to enable helpers. It’s done automagically wherever possible. However, one can set it explicitly anywhere:
Magic::Presenter.with view_context: ApplicationController.new.view_context do
# put the code that uses helpers within presenters here
end
Note
A valid request
may be needed for URL helpers to get host info.
🧙 Magic
It’s based on Magic Decorator, so get familiar with that one as well.
Presentable scope
Magic::Presentable
is mixed into ActiveModel::API
by default.
It means that any model, be it ActiveRecord::Base
, Mongoid::Document
or whatever else, is magically presentable.
Presenter class inference
Presenters provide automatic class inference for any model based on its class name powered by Magic Lookup.
For example, MyNamespace::MyModel.new.decorate
looks for MyNamespace::MyPresenter
first.
When missing, it further looks for decorators for its ancestor classes, up to ObjectPresenter
.
Mapping rules
-
MyObject
→MyObjectPresenter
-
MyModel
→MyPresenter
-
MyRecord
→MyPresenter
Tip
That’s why ApplicationPresenter
presents ApplicationRecord
alongside all its descendants automagically with no extra code.
When in doubt, one can use Magic::Presenter.name_for
:
Magic::Presenter.name_for Person # => "PersonPresenter"
Preloading
Note
Magic Lookup doesn’t try to autoload any classes, it searches among already loaded ones instead. Thus, presenters should be preloaded to be visible via lookups.
This is done automatically in both test and production environments by Rails. All the application’s presenters and models are eagerly loaded before normal and reverse lookups by Magic Presenter as well. So, normally one shouldn’t worry about that.
Important
When developing a Rails engine that defines its own presenters, one should take care of the preloading themselves.
That could be done in an initializer with a helper method provided:
Rails.application.config.to_prepare do
Magic.eager_load :presenters, engine: MyLib::Engine
end
Class methods delegation
Missing class methods of a presenter are delegated to a matching model class if the latter can be inferred unambiguously.
Magic::Lookup::Error
is raised otherwise.
In views
Important
Every object passed to views is decorated automagically.
This involves both implicit instance variables and locals
passed explicitly.
Helpers
One can call helpers directly without explicit helper
or h
:
class PersonPresenter < Magic::Presenter::Base
def self.links
[ link_to('All', model_class) ]
end
def link(...) = link_to(name, self, ...)
end
View context
View context is set automagically to enable helpers:
- in views,
- in controller actions,
- in mailer actions.
Generators
Note
The built-in helper
generator is overridden with presenter
one to generate presenters instead of helpers.
Development
After checking out the repo, run bin/setup
to install dependencies. Then, run rake spec
to run the tests. You can also run bin/console
for an interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
.
Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/Alexander-Senko/magic-presenter. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.
License
The gem is available as open source under the terms of the MIT License.
Code of Conduct
Everyone interacting in the Magic Presenter project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.