Difference between render functions in Phoenix

Question

I'm trying to understand the difference between the different render functions in Phoenix. Specifically, I notice there are several different render functions in a Phoenix View and a Phoenix Template.

For example, within a Phoenix Controller, it's common to see something like this:

# assume this is UserController
def index(conn, _params) do
    users = Repo.all(Users) # let's assume that this gives you all your users
    render conn, "index.html", users: users
end

Within the index.html template associated with this View (i.e. UserView), you can see something like this:

# index.html
<ul>
    <%= for user <- @users do %>
        <li><%= render "user.html", user: user %></li>
    <% end %>
</ul>

# user.html
<p><%= @user.name %></p>

My understanding is that the render function inside of the index.html template is compiled to a render function inside of the UserView. Also, after digging around in iex, it seems like the render function in the UserController's index action comes from Phoenix.Controller.render/3.

However, I notice that inside of the default app.html.eex template file, there's a render function that looks like this:

<%= render @view_module, @view_template, assign %>

This doesn't seem to match the signatures of the previous render functions. Can anyone help explain where this render is coming from and how it works?

Aleksei Matiushkin Aleksei Matiushkin · Accepted Answer · 2017-04-13T05:17:39

Phoenix.View has a descriptive documentation, and if still in doubt, there is a source code for Phoenix.View.render/3 and Phoenix.Controller.render/{1,3,4} on hand.

The related quote from the documentation:

This inner representation allows us to render and compose templates easily. For example, if you want to render JSON data, we could do so by adding a “show.json” entry to render/2 in our view:
defmodule YourApp.UserView do
  use YourApp.View    
  def render("show.json", %{user: user}) do
    %{name: user.name, address: user.address}
  end
end

Difference between render functions in Phoenix

2 Answers