JbuilderCacheMulti

Useful when you need to retrieve fragments for a collection of objects from the cache. This plugin gives you method called 'cache_collection!' which uses fetch_multi (new in Rails 4.1) to retrieve multiple keys in a single go.

This means less queries to the cache == faster responses. If items are not found, they are writen to the cache (individualy. memcache doesn't support writing items in batch...yet).

Tested with Rails 4.1 + Memcached + Dalli

Installation

Add this line to your application's Gemfile:

gem 'jbuilder_cache_multi'

And then execute:

$ bundle

Or install it yourself as:

$ gem install jbuilder_cache_multi

Usage

Renders the given block for each item in the collection. Accepts optional 'key' attribute in options (e.g. key: 'v1').

Note: At the moment, does not accept the partial name as an argument (#todo)

Examples:

json.cache_collection! @people, expires_in: 10.minutes do |person|
  json.partial! 'person', :person => person
end

# Or with optional key

json.cache_collection! @people, expires_in: 10.minutes, key: 'v1' do |person|
  json.partial! 'person', :person => person
end

# Or with a proc as a key 

json.cache_collection! @people, expires_in: 10.minutes, key: proc {|person| person.last_posted_at } do |person|
  json.partial! 'person', :person => person
end

NOTE: If the items in your collection don't change frequently, it might be better to cache the entire collection like this: (in which case you don't need this gem)

json.cache! @people do
  json.partial! 'person', collection: @people, as: :person
end

Or you can use a combination of both! This will cache the entire collection. If a single item changes it will use read_multi to get all unchanged items and regenerate only the changed item(s).

json.cache! @people do
  json.cache_collection! @people do |person|
    json.partial! 'person', :person => person
  end
end

Last thing: If you are using a collection for the cache key, may I recommend the 'scope_cache_key' gem? (check out my fork for a Rails 4 version: https://github.com/joshblour/scope_cache_key). It very quickly calculates a hash for all items in the collection (MD5 hash of updated_at + IDs).

You can also conditionally cache a block by using cache_collection_if! like this:

json.cache_collection_if! do_cache?, @people, expires_in: 10.minutes do |person|
  json.partial! 'person', :person => person
end

Usage with ActiveRecord::Relation

Sometimes queries can be very complex and populating models from queries with many includes take up the majority of time. After checking the cache, it is than obvious populating all these models was not necessary as we have a hit. Why not checking the cache after just using a simple query to build the cache-key and only fire the complex query for those models, that do not exist in the cache? Well this is possible.

For these cases you can paste the ActiveRecord::Relation and cache_collection! will:

unscope all includes for the initial query to build all cache_key's (make sure you use joins for statements that are use in where)
gets the result from cache with Rails.cache.read_multi for existing cache_key hits
gets all missed hits from the database with complex includes and all fields
builds the block with all data
uses Rails.cache.write_multi if available to populate the cache with the missed values

json.cache_collection! Post.includes(:author) do |post| json.partial! 'post', :post => post end

Todo

Add support for passing a partial name as an argument (e.g. json.cache_collection! @people, partial: 'person') or maybe even just "json.cache_collection! @people" and infer the partial name from the collection...
When rendering other partials, use the hash of THAT partial for the cache_key (I beleieve it currently uses the view from where cache_collection! is called to calculate the cache_key) #not_good

Contributing

Fork it ( https://github.com/joshblour/jbuilder_cache_multi/fork )
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create a new Pull Request

Testing

bundle install
appraisal install
appraisal rake test

Credit

Inspired by https://github.com/n8/multi_fetch_fragments. Thank you! And of course https://github.com/rails/jbuilder

quorak/jbuilder_cache_multi