rendering partial does not render the layout-CodePudding

I have an action show that has a correspondent show.html.erb file as well. What I'm trying to do is add an "early return" so to say in case the record doesn't exist:

class MessagesController < ApplicationController
  def show
    unless Message.exists?(mid: params[:id])
      return render partial: 'messages/expired'
    end

    # rendered by views/messages/show.html.erb
  end
...

In case the message exists, this works fine and I can see rails rendering all the files/layouts:

19:51:19 web.1  |   Message Exists? (0.3ms)  SELECT 1 AS one FROM "messages" WHERE "messages"."mid" = $1 LIMIT $2  [["mid", "01G7FD3BBGE2EJH3ABVC5RRWAG"], ["LIMIT", 1]]
19:51:19 web.1  |   ↳ app/controllers/messages_controller.rb:3:in `show'
19:51:19 web.1  |   Rendering layout layouts/application.html.erb
19:51:19 web.1  |   Rendering messages/show.html.erb within layouts/application
19:51:19 web.1  |   Rendered messages/show.html.erb within layouts/application (Duration: 1.9ms | Allocations: 1159)
19:51:19 web.1  |   Rendered layouts/_nav.html.erb (Duration: 0.4ms | Allocations: 129)
19:51:19 web.1  |   Rendered layout layouts/application.html.erb (Duration: 82.3ms | Allocations: 26506)
19:51:19 web.1  | Completed 200 OK in 94ms (Views: 88.6ms | ActiveRecord: 2.6ms | Allocations: 29578)

but here is the weird thing: in case the record doesn't exist, Rails does render the partial, but only the partial:

19:52:56 web.1  |   Message Exists? (0.6ms)  SELECT 1 AS one FROM "messages" WHERE "messages"."mid" = $1 LIMIT $2  [["mid", "01G7FD3BBGE2EJH3ABVC5RRWA"], ["LIMIT", 1]]
19:52:56 web.1  |   ↳ app/controllers/messages_controller.rb:3:in `show'
19:52:56 web.1  |   Rendered messages/_expired.html.erb (Duration: 0.1ms | Allocations: 22)
19:52:56 web.1  | Completed 200 OK in 10ms (Views: 1.3ms | ActiveRecord: 0.6ms | Allocations: 885)
19:52:56 web.1  |

I don't remember seeing this behavior before so I'm really confused...what am I doing wrong? Honestly, I'm a little burned out so it could be I can't see something that is right in my face but I simply can't understand why is this happening...

Interestingly, if do render 'messages/expired', without the partial: and rename the file to remove the underscore so it is not a partial anymore, it works:

19:56:04 web.1  |   ↳ app/controllers/messages_controller.rb:3:in `show'
19:56:04 web.1  |   Rendering layout layouts/application.html.erb
19:56:04 web.1  |   Rendering messages/expired.html.erb within layouts/application
19:56:04 web.1  |   Rendered messages/expired.html.erb within layouts/application (Duration: 0.1ms | Allocations: 141)
19:56:04 web.1  |   Rendered layouts/_nav.html.erb (Duration: 0.4ms | Allocations: 124)
19:56:04 web.1  |   Rendered layout layouts/application.html.erb (Duration: 2.6ms | Allocations: 2627)
19:56:04 web.1  | Completed 200 OK in 7ms (Views: 3.4ms | ActiveRecord: 2.1ms | Allocations: 5494)

wild guess: it has something to do with the fact that all of that is happening on show so some Rails' default kicks in.

CodePudding user response：

render method in controllers processes its arguments a bit differently than in views.

# NOTE: :body, :plain, :html, :inline, :partial
#       will render without a layout
#       unless :layout option is specified
#       https://github.com/rails/rails/blob/v7.0.3/actionview/lib/action_view/layouts.rb#L431

def show
  # Without layout
  render partial: "expired"           # renders "messages/_expired"

  # With layout
  render "expired"                    # renders "messages/expired"
  render template: "messages/expired" # renders "messages/expired"
  render "_expired"                   # renders "messages/_expired"

  # Doesn't work
  render partial: "expired",          # renders "messages/_expired"
    layout: "application"             # in "layouts/_application" # <= doesn't exist
end

In the view:

# Without layout
<%= render "expired" %>                      # renders "messages/_expired"
<%= render partial: "expired" %>             # renders "messages/_expired"
<%= render template: "messages/_expired" %>  # renders "messages/_expired"
<%= render template: "messages/expired" %>   # renders "messages/expired"


# With layout
<%= render template: "messages/expired", layout: "layouts/application" %>
                                             # renders "messages/expired"
                                             # in "application" layout (again)
<%= render partial: "expired", layout: "application" %>
                                             # renders "messages/_expired"
                                             # in "messages/_application" partial layout

You can keep _expired partial or rename it to expired and just use the appropriate render call.

https://api.rubyonrails.org/classes/AbstractController/Rendering.html#method-i-render

https://api.rubyonrails.org/classes/ActionView/Helpers/RenderingHelper.html#method-i-render