Why

What

Both ActionView and ActionController has render method.

• render

• render this one has render formats: [:json, :html], as search :formats in the source code

It’s confusing the documentation mix those two methods together.

How

The controller is able to render explicitly or implicitly.

• Implicit: If you do not explicitly render something at the end of a controller action, Rails will automatically look for the action_name.html.erb template in the controller’s view path and render it.

• Explicit:

• render to render whatever stuff in named format. The content may be current action’s template, some other action’s template in or not in the same controller, a file, a raw string, etc.

• respond_to to describe what to return for different requested formats.

Where

When

respond_to might play a supplemental role for render. As the doc states: render renders a template and assigns the result to self.response_body. And since the very beginning, only two formats are supported natively: html & json. While respoind_to act as a DSL, allowing us to describe what to respond for different formats requested. The doc for respond_to constantly mentions web-service, which it means certain rack-compliant web server that brings requested format information to our rails controller. So within respond_to, we can define what to return with the format object.

references: What’s the difference between using render instead of respond_with/to in a Rails API? - Stack Overflow

Who

It’s very interesting to read ActionController::Base and ActionView::Base. Those two Base classes play vital roles in dealing with web request.