Representers for Rails

A possible representer solution, i.e. no view logic in model code.

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Problem: Display Methods are not well placed either in

* models: Violation of the MVC principle.

* helpers: No Polymorphism.

Solution:

A thin proxy layer over a model, with access to the controller, used by the view or controller.

IMPORTANT NOTE:

As of yet it is needed to copy the representer/views/representers/collection

directory to the corresponding location in app/views/representers/collection.

This is only needed if you wish to use the collection rpresenter.

Note: Rewrite the collection templates as needed, they are rather basic.

* Getting a representer in a view or a controller.

Call representer_for:

Note: By convention, uses Representers::Model::Class::Name, thus prefixing Representers:: to

the model class name.

presenter_instance = representer_for model_instance

* Getting a collection representer in a view.

The collection representer renders each of the given items with its representer.

Call collection_presenter_for:

collection_presenter_instance = collection_presenter_for enumerable_containing_model_instances

Rendering a list.

collection_presenter_instance.list

Rendering a collection.

collection_presenter_instance.collection

Rendering a table.

collection_presenter_instance.table

Rendering a pagination.

Note: Only works if the passed parameter for collection_presenter_for is a PaginationEnumeration.

collection_presenter_instance.pagination

* Writing filtered delegate methods on the representer.

Will create two delegate methods first_name and last_name that delegate to the model.

model_reader :first_name, :last_name

Will create a description delegate method that filters the model value through h.

model_reader :description, :filter_through => :h

Will create a description delegate method that filters the model value through first textilize, then h.

model_reader :description, :filter_through => [:textilize, :h]

Will create both a first_name and last_name delegate method

that filters the model value through first textilize, then h.

model_reader :first_name, :last_name, :filter_through => [:textilize, :h]

Note: Filter methods can be any method on the representer with arity 1.

* Rendering representer templates

Use render_as(template_name, format = nil).

Gets a Representers::Model::Class instance

presenter = representer_for Model::Class.new

Gets a Representers::<model_instance.class.name> instance

presenter = representer_for model_instance

Renders the 'example' partial in representers/model/class.

Note: Renders a format depending on the request. ../index.text will render example.text.erb.

presenter.render_as :example

Renders the 'example.text.erb' partial in representers/model/class.

presenter.render_as :example, :text

* Rails Helpers in Representers

Use helper as in the controller.

helper ActionView::Helpers::UrlHelper helper ApplicationHelper

Note: It is helpful to create a superclass to all representers in the project

with generally used helpers.

We use Representers::Project a lot, for example. See example below.

* Controller Delegate Methods

Use controller_method(*args).

Delegates current_user and logger on the representer to the controller.

controller_method :current_user, :logger

* Big Example

The following classes all have specs of course ;) But are not shown since they don't help the example.

Representers superclass for this project.

We include all of Rails' helpers for the representers in this project.

Also, we include the ApplicationHelper.

We delegate logger and current_user calls in the representers to

the active controller.

class Representers::Project < Representers::Base

All of Rails' standard helpers.

helper ActionView::Helpers::ActiveRecordHelper helper ActionView::Helpers::TagHelper helper ActionView::Helpers::FormTagHelper helper ActionView::Helpers::FormOptionsHelper helper ActionView::Helpers::FormHelper helper ActionView::Helpers::UrlHelper helper ActionView::Helpers::AssetTagHelper helper ActionView::Helpers::PrototypeHelper helper ActionView::Helpers::TextHelper

helper ApplicationHelper

controller_method :logger, :current_user

end

All items have a description that needs to be filtered by textilize.

class Representers::Item < Representers::Project model_reader :description, :filter_through => :textilize

Use price in the view as follows:

= representer.price - will display e.g. 16.57 CHF, since it is filtered first through localize_currency

model_reader :price, :filter_through => :localize_currency

Converts a database price tag to the users chosen value, with the users preferred currency appended.

If the user is Swiss, localize_currency will convert 10 Euros to "16.57 CHF"

def localize_currency(price_in_euros) converted_price = current_user.convert_price(price_in_euros) "#{converted_price} #{current_user.currency.to_s}" end end