Module: CachedAttribute::ClassMethods

Defined in:
lib/cached_attribute.rb

Instance Method Summary collapse

Instance Method Details

#cached_attribute(attr, opts = {}) ⇒ Object

specifies that the attribute attr should be cached. By default, the cache specified by the instance variable Cache is used. cached_attribute will also memoize the attribute by default.

Options:

:ttl         - The ttl (in seconds) for the cached attribute. Defaults to 5 minutes.
:cache       - The cache store object to use for caching. Must respond to #get (with block)
               and #delete and #set or #put (key, value, expiry).
:identifier  - A block that takes a single parameter (of the object containing the cached
               attribute) and returns an identifier unique to that object. Defaults to
               lambda {|s| s.id}, which works fine for activerecord objects.
:memoize     - Whether the return value should be memoized into an instance variable.
               Defaults to true.

Example:

class ComplicatedModel < ActiveRecord::Base

  def expensive_operation
    ... something expensive ...
  end

  # caches the calls to expensive_operation
  cached_attribute :expensive_operation

end



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# File 'lib/cached_attribute.rb', line 37

def cached_attribute(attr, opts = {})

  cache = opts[:cache] || (defined?(CACHE) && CACHE)
  ttl = opts[:ttl] || 300

  define_method("#{attr}_cache_key") do |*prms|
    if prms.present?
      identifier = prms.pretty_inspect # pretty inspect works nicely because it properly escpaes all the params into one string
    else
      identifier = opts[:identifier] ? opts[:identifier].call(self).to_s : self.id.to_s
    end
    # need to special case when we're caching class methods
    klass_string = "#{self.class == Class ? self.name + '::self' : self.class.name}"
    "#{klass_string}::#{attr}::#{Digest::SHA1.hexdigest(identifier)}"
  end

  define_method("#{attr}_with_caching") do |*prms|
    if cache && (instance_variable_get("@#{attr}").nil? || prms.present?)
      cache.fetch(send("#{attr}_cache_key", *prms), ttl) do
        send("#{attr}_without_caching", *prms)
      end
    else
      send("#{attr}_without_caching", *prms)
    end
  end

  alias_method "#{attr}_without_caching", attr
  alias_method attr, "#{attr}_with_caching"

  unless opts[:memoize] == false

    define_method("#{attr}_with_memoization") do |*prms|
      value = instance_variable_get("@#{attr}")
      if value.nil? || prms.present? # skip memoization if there are prms
        value = instance_variable_set("@#{attr}", send("#{attr}_without_memoization", *prms))
      end
      value
    end

    alias_method "#{attr}_without_memoization", attr
    alias_method attr, "#{attr}_with_memoization"
  end

  define_method("invalidate_#{attr}") do |*prms|
    if cache
      cache_key = send("#{attr}_cache_key", *prms)
      cache.delete(cache_key)
    end
  end

  # refreshs the cached attribute
  define_method("refresh_#{attr}") do |*prms|
    if cache
      set_method = cache.respond_to?(:set) ? :set : :put
      val = send("#{attr}_without_caching")
      cache.send(set_method, send("#{attr}_cache_key", *prms), val, ttl)
    end
  end

end