stale?

Sets the etag and/or last_modified on the response and checks it against the client request. If the request doesn’t match the options provided, the request is considered stale and should be generated from scratch. Otherwise, it’s fresh and we don’t need to generate anything and a reply of 304 Not Modified is sent.

Parameters:

• :etag.

• :last_modified.

• :public By default the Cache-Control header is private, set this to true if you want your application to be cachable by other devices (proxy caches).

• :template By default, the template digest for the current controller/action is included in ETags. If the action renders a different template, you can include its digest instead. If the action doesn’t render a template at all, you can pass template: false to skip any attempt to check for a template digest.

Example:

def show
  @article = Article.find(params[:id])

  if stale?(etag: @article, last_modified: @article.created_at)
    @statistics = @article.really_expensive_call
    respond_to do |format|
      # all the supported formats
    end
  end
end

You can also just pass a record where last_modified will be set by calling updated_at and the etag by passing the object itself.

def show
  @article = Article.find(params[:id])

  if stale?(@article)
    @statistics = @article.really_expensive_call
    respond_to do |format|
      # all the supported formats
    end
  end
end

When passing a record, you can still set whether the public header:

def show
  @article = Article.find(params[:id])

  if stale?(@article, public: true)
    @statistics = @article.really_expensive_call
    respond_to do |format|
      # all the supported formats
    end
  end
end

When rendering a different template than the default controller/action style, you can indicate which digest to include in the ETag:

def show
  super if stale? @article, template: 'widgets/show'
end