what is the difference between link_to, redirect_to, and render?

Question

I am confused about the main difference(s) among link_to, redirect_to and render in Rails. anyone can please explain.

Answer 1

I actually just wrote a blog post about this. The most important bits are copied below (with modifications).

Controller Methods: render vs. redirect_to

render and redirect_to are the two ways that controller actions end (generally speaking). To understand how they work, let's review what controllers do in a Rails app:

• A user tries to access a page.
  (http://localhost:3000/books/index.html)
• Under the hood, the browser sends an HTTP request for the specified path on the server.
  (GET /books/index.html)
• The Rails routing system then looks up which controller corresponds to the given request path.
  (books GET /books/index(.:format) books#index)
• The controller prepares some data and then tells the server what response (i.e., what HTTP header/body content) to send back to the client.

This last step occurs explicitly when you call render or redirect_to, or implicitly if you leave it out.

That is,

def index
  @books = Book.all
end

is the same as

def index
  @books = Book.all
  render :index
end

render :index says, ‘combine the data I've prepared (@books = Book.all) with the books/index.html.erb view template to generate a complete HTML document, then send that back to the client.’

redirect_to @book says, ‘tell the client to start the whole process over again, issuing a new GET request to url_for(@book).

If you omit both, the action will render a template with the same name as the action itself. In other words, you only need to call render explicitly when the view template you want doesn’t match the action you’re rendering it from.

Note that not every controller action has a corresponding view template. Generally, #create, #update, and #destroy (which are all routed to non-GET HTTP requests) attempt to make some change to the database and then either redirect_to some resource (if it succeeded) or re-render the form that preceded it, along with any errors (if it failed).

As the official guides explain (emphasis mine),

These two methods [render and redirect_to] represent the two basic action archetypes used in Action Controllers: Get-and-show and do-and-redirect. Most actions are variations on these themes.

---

View Methods: render vs. link_to

render is also used within view templates themselves. Rather than generating a complete HTML document, it's used to insert a partial view template into a larger one. Here's the upshot:

• You can create partial view template files to be inserted into your standard templates (think of them as modular page components).
• Filenames of partials must begin with an underscore (e.g., _nav.html.erb).
• Use render 'nav' if you want to include the _nav.html.erb partial from a view located in the same folder.
• Use render 'shared/nav' if you want to include the partial at app/views/shared/_nav.html.erb from any view in your project.
• Various options and shorthand syntaxes exist for passing data into a partial, rendering multiple partials from a collection object, and more. See the guides for details.

link_to is just a convenience method for inserting anchor tags (a href tags) into your view templates. This is useful because a lot of the URLs you'll want to link to are other pages within your application, and those URLs can be referenced using objects or "helper methods", like so:

= link_to 'Back', books_path   # renders as Back
= link_to 'View', @book        # renders as View or similar