Module: CachedSingleton

Defined in:
lib/cached_singleton/version.rb,
lib/cached_singleton/cached_singleton.rb

Constant Summary collapse

VERSION = 
'0.0.2'
@@cache_strategy = 
nil

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.default_cache_strategy ⇒ Object 



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# File 'lib/cached_singleton/cached_singleton.rb', line 10

def self.default_cache_strategy
  unless @@cache_strategy
    raise RuntimeError.new('default cache strategy not set')
  end
  @@cache_strategy
end

.default_cache_strategy=(cache_strategy) ⇒ Object 



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# File 'lib/cached_singleton/cached_singleton.rb', line 6

def self.default_cache_strategy=(cache_strategy)
  @@cache_strategy = cache_strategy
end

.included(model) ⇒ Object 



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# File 'lib/cached_singleton/cached_singleton.rb', line 17

def self.included(model)
  model.class_eval do

    class << self
      def cache
        CachedSingleton.default_cache_strategy
      end

      def singleton_cache_key
        "/#{self.name}"
      end

      def instance
        # Fetch in cache
        m = self.cache.read(singleton_cache_key)
        return m if m

        # Get it in from the DB or create it
        transaction do
          # We ensure no other process is trying to SELECT OR INSERT the same record by locking
          # the entire table (read + write) during the transaction
          connection.execute("LOCK TABLE #{table_name} IN EXCLUSIVE MODE")
          m = first || create
        end

        # Save it in cache if it's in the DB
        self.cache.write(singleton_cache_key, m) if m.try(:persisted?)

        m
      end
    end

    after_commit :expire_cache
  end
end

Instance Method Details

#expire_cache ⇒ Object 



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# File 'lib/cached_singleton/cached_singleton.rb', line 53

def expire_cache
  self.class.cache.delete(self.class.singleton_cache_key) if (!new_record? || destroyed?)
end