Double render

Explanation

Rails developers often encounter the

"Can only render or redirect once per action"

error, typically due to a misunderstanding of how render works.

The error arises when there are multiple render calls within the same action.

For instance, consider the following problematic code:

def show
  @event = Event.find(params[:id])

  if @event.remote?
    render action: "roblox_show"
  end

  render action: "show"
end

Here if @event.remote? returns true both render action: "roblox_show" and render action: "show" are called simultaneously.

To resolve this issue, ensure a single call to render or redirect in a code path.

Using return helps in this case:

def show
  @event = Event.find(params[:id])

  if @event.remote?
    render action: "roblox_show"
    return
  end

  render action: "show"
end

An alternative approach, leveraging implicit render, can be used without errors:

def show
  @event = Event.find(params[:id])

  if @event.remote?
    render action: "roblox_show"
  end
end

This version successfully renders the appropriate template based on the condition, addressing the error and maintaining code clarity.

Indeed, if @event.remote? returns false, the show method returns and ActionController returns the corresponding view for you.

Voilà!