stale?

Sets the `etag` and/or `last_modified` on the response and checks them against the request. If the request doesn’t match the provided options, it is considered stale, and the response should be rendered from scratch. Otherwise, it is fresh, and a `304 Not Modified` is sent.

#### Options

See #fresh_when for supported options.

#### Examples

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

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

You can also just pass a record:

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

`etag` will be set to the record, and `last_modified` will be set to the record’s `updated_at`.

You can also pass an object that responds to `maximum`, such as a collection of records:

def index
  @articles = Article.all

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

In this case, `etag` will be set to the collection, and `last_modified` will be set to `maximum(:updated_at)` (the timestamp of the most recently updated record).

When passing a record or a collection, you can still specify other options, such as `:public` and `:cache_control`:

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

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

The above will set `Cache-Control: public, no-cache` in the response.

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

def show
  super if stale?(@article, template: "widgets/show")
end

# File actionpack/lib/action_controller/metal/conditional_get.rb, line 236
    def stale?(object = nil, **freshness_kwargs)
      fresh_when(object, **freshness_kwargs)
      !request.fresh?(response)
    end