# 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).

## 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

1. Fork it ( https://github.com/joshblour/jbuilder_cache_multi/fork )
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. 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