Fragment Caching and AA

[Phazz]

Maybe a stupid question.

I am wondering if it is possible to do fragment caching from AA DSL, something like :

cache "user" do
 index do
    column :user
 end
end

Thanks,

[janko]

It is not possible at the moment. It could theoretically work with #cache being inside:

index do
  cache "user" do
    column :user
  end
end

But since a custom templating language (Abre) is being used, it doesn't work. The method #cache exists there, but the buffer can't be captured, because of how Abre works.

[zorab47]

Here is a helper method I use to cache arbre output. It could probably be
improved by wrapping the output in a text_node rather than a div,
but I haven't tried it yet.

# application_helper.rb

# Caches Arbre output.
#
# context - ActiveAdmin instance context
# args    - Arguments passed to Rails.cache calls.
#
# Yielding the first time adds to the output buffer regardless of the
# returned value. The missed cache must be handled carefully.
#
# Returns yielded Arbre on cache miss OR an HTML string wrapped in
# an Arbre div on cache hit.
def cache_arbre(context, *args)
  if controller.perform_caching
    if Rails.cache.exist?(*args)
      context.instance_eval do
        div(Rails.cache.read(*args))
      end
    else
      Rails.cache.write(*args, yield.to_s)
    end
  else
    yield
  end
end

Usage would be like the following:

ActiveAdmin.register User do
  show do
    arbre_cache(self, user.cache_key) do
      attributes_table do
        row :name
        row :email
        row :expensive_calculation
      end
    end
  end
end

[seanlinsley]

Hi @zorab47, thanks for the tip! But trying it out, the div doesn't seem necessary. This works for me:

module ApplicationHelper

  def cache_arbre(*args)
    if controller.perform_caching
      opts = args.extract_options!.merge namespace: :arbre
      Rails.cache.fetch(*args, opts) { yield.to_s }
    else
      yield
    end
  end

end

I also updated it to use a namespace to prevent key collisions.

[zorab47]

In my usage the cached content would only be displayed if it was wrapped in an Arbre element. The one exception is when the string is the last value in the block.

As an example:

show do
  panel "Display Test" do
    "Text which won't be rendered."
    "Last string in block, which will be rendered."
  end
end

From what I've determined Arbre handles a block returning a string by automatically wrapping it in a text_node. See https://github.com/gregbell/arbre/blob/master/lib/arbre/element.rb#L43. The other strings within the block are lost.

So, If cached content is followed by more Arbre elements it won't be rendered.

[Fivell]

@zorab47, I can confirm you're right , and cached Arbre blocks are empty in some cases.

[paquettej]

I am displaying a table with ActiveAdmin using the "Index as Table" functionality:

  index :pagination_total => false do

    if Ability.new(current_user).can? :manage, :metric
        selectable_column
    end

    column '' do |metric|
        links = link_to(metric.icon, admin_metric_path(metric), :title => metric.comment)
        links += link_to(metric.data_icon, admin_metric_path(metric)) unless metric.datum_ids.empty?
        links
    end

    column 'Status', :success, sortable: :success do |metric|
        metric.success == 1 ? status_tag('Success', :ok) : status_tag('FAILED', :error)
    end
    column 'When (UTC)', :createddttm
    column 'What', :metric_name
    column 'Area',    :logarea
    column 'Subarea', :subarea
    column 'Value',   :value
    column 'Machine', :machine_name, sortable: 'machinename.machinename'
    column 'Domain',  :domain_name, sortable: 'domain.domainname'
    column 'Product', :product_name, sortable: 'product.productname'
    column 'Version', :product_version, sortable: 'product.productversion'
    column 'Install Type', :install_type, sortable: 'product.productinstalltype'
    column 'Lang', :language
    column 'Duration', :duration
  end

Given that the row data does not change, I would like to add row level caching with a long expiry time but I can't figure out how to hook into the row rendering code in Arbre.

I'd love to see a way to cache each row.

[zorab47]

Another thing to note with the above cache_arbre helper is that it doesn't handle changes to the template like calls to cache in ActionView. It requires that the cache be cleared when the template changes.

[grgr]

If you want to use div, text_node or other arbre elements you could write the helper like this:

  def aa_cache(context, cache_key, &block)
    if controller.perform_caching
      if Rails.cache.exist?(cache_key)
        html = Rails.cache.read(cache_key)
        context.text_node(html)
      else
        Arbre::Element.new(context).build(&block)
        Rails.cache.write(cache_key, context.current_arbre_element.content)
      end 
    end 
  end 

[zorab47]

A new approach to caching Arbre content that is less prone to miss elements. The improvement is tracking which elements were added and building a string to cache from their content.

Available as a gist: https://gist.github.com/zorab47/eda38bc72a5d1153b73b

# Caches Arbre elements in the `Rails.cache`.
#
# Yielding the first time adds to the output buffer regardless of the
# returned value. A cache miss must be handled separately from a hit
# to avoid double rendering.
#
# Returns yielded Arbre on cache miss OR an HTML string wrapped in
# an text node on cache hit.
def cache_arbre(context, *args, &block)
  if controller.perform_caching
    if Rails.cache.exist?(*args)
      context.text_node(Rails.cache.read(*args))
    else
      Rails.cache.write(*args, arbre_appended_children_content(context, &block))
    end
  else
    yield
  end
end

# Returns HTML content for Arbre elements appended to a context.
#
# Due to the complexities of Arbre content buffering it is difficult to get
# the content of an arbitrary set of Arbre elements without the use of a
# wrapping element like a `div`.
#
# Example
#
#    Arbre::Context.new do
#      h1 "Capturing Children Content"
#
#      content = arbre_appended_children_content(self) do
#        para "Paragraph 1"
#        para "Paragraph 2"
#      end
#    end
#
#    content # => "<p>Paragraph 1</p>\n<p>Paragraph 2</p>\n"
#
# Unlike this simple example which only returns the content of Paragraph 2
# because it is the only object returned from the block.
#
#    Arbre::Context.new do
#      h1 "Example of "
#
#      content = begin
#        para "Vanishing Paragraph 1"
#        para "Paragraph 2"
#      end.to_s
#    end
#
#    content # => "<p>Paragraph 2</p>\n"
#
def arbre_appended_children_content(context)
  children      = context.current_arbre_element.children
  original_size = children.size
  content       = "".html_safe
  result        = yield

  if (children.size > original_size)
    content = "".html_safe

    children[original_size .. -1].each do |child|
      content << child.to_s
    end
  else
    # No children added, return the output from yield. This could be when
    # content was generated from a partial via `render`.
    content = result.to_s
  end

  content
end

[zorab47]

@varyonic do you think this workaround can be added to ActiveAdmin or Arbre? Otherwise I may pull it into a gem for convenience.

[varyonic]

It looks plausible as an Arbre PR. I don't spend time on Arbre optimization as I have way more issues with ransack filters allowing expensive SQL.

[lautarocastillo]

Is there any way to perform Fragment caching with AA?? I couldn't make it work yet!

[itkin]

+1