Rails: Render view from outside controller

Question

I'm trying to create an HTML string using a view. I would like to render this from a class that is not a controller. How can I use the rails rendering engine outside a controller? Similar to how ActionMailer does?

Thanks!

Answer 1

Rails 5 and 6 support this in a much more convenient manner that handles creating a request and whatnot behind the scenes:

rendered_string = ApplicationController.render(
  template: 'users/show',
  assigns: { user: @user }
)

This renders app/views/users/show.html.erb and sets the @user instance variable so you don't need to make any changes to your template. It automatically uses the layout specified in ApplicationController (application.html.erb by default). Full documentation can be found here.

The test shows a handful of additional options and approaches.

Answer 2

You can use ActionView::Base to achieve this.

view = ActionView::Base.new(ActionController::Base.view_paths, {})
view.render(file: 'template.html.erb')

The ActionView::Base initialize takes:

1. A context, representing the template search paths
2. An assigns hash, providing the variables for the template

If you would like to include helpers, you can use class_eval to include them:

view.class_eval do
  include ApplicationHelper
  # any other custom helpers can be included here
end

Answer 3

In Rails 5:

view = ActionView::Base.new(ActionController::Base.view_paths)
view.render(file: 'template.html.erb')

In Rails 6.1:

lookup_context = ActionView::LookupContext.new(ActionController::Base.view_paths)
context = ActionView::Base.with_empty_template_cache.new(lookup_context, {}, nil)

renderer = ActionView::Renderer.new(lookup_context)
renderer.render(context, { file: 'app/views/template.html.erb' })

• ActionView::Renderer.new() takes a lookup_context arg, and render() method takes a context, so we set those up first
• ActionView::Base is the default ActiveView context, and must be initialized with with_empty_template_cache method, else render() will error
• The {}, nil are required assigns and controller args, which used to default to {}, nil in Rails 5
• Rails 6.1 requires a full filepath file: 'app/views/template.html', whereas Rails 5 only required the filename

Answer 4

There is no need to over bloat your app with too many gems. As we know ERB is already included in your Rails app.

@jdf = JDF.new
@job = ERB.new(File.read(Rails.root + "app/views/entries/job.xml.erb"))
result =  @job.result(binding)

Above there is snippet of code of an app I'm working on.

• @jdf is a object to be evaluated in the erb view.
• In my case I needed to render xml.
• result is a string to be saved or sent anywhere you like.

Answer 5

"I'm trying to create an HTML string using a view." -- If you mean you're in the context of a view template, then just use a helper method or render a partial.

If you're in some other "Plain Old Ruby Object", then keep in mind you're free to use the ERB module directly:

erb = ERB.new("path/to/template")
result = erb.result(binding)

The trick is getting that 'binding' object that gives the context for the code in the template. ActionController and other Rails classes expose it for free, but I couldn't find a reference that explains where it comes from.

http://www.ruby-doc.org/stdlib-2.2.0/libdoc/erb/rdoc/ERB.html#method-i-result

Answer 6

Calling directly render method on ApplicationController may raise error

 Helper Devise: could not find the `Warden::Proxy` instance on request environment

Instead we can use ApplicationController.renderer.render like

 rendered_string = ApplicationController.renderer.render(
     partial: 'users/show',
     locals: { user: user }
)

Answer 7

Technically, ActionMailer is a subclass implementation of AbstractController::Base. If you want to implement this functionality on your own, you'll likely want to inherit from AbstractController::Base as well.

There is a good blog post here: https://www.amberbit.com/blog/2011/12/27/render-views-and-partials-outside-controllers-in-rails-3/ that explains the steps required.

Answer 8

For future reference, I ended up finding this handy gem that makes this a breeze:

https://github.com/yappbox/render_anywhere

Answer 9

Best to render the view using a controller, as that's what they're for, and then convert it to a string, as that is your ultimate goal.

require 'open-uri'
html = open(url, &:read)