Write documentation for the cache stores.

1 files changed, 103 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/cache.rb b/activesupport/lib/active_support/cache.rb
index 51a6309dce..e62cec6fcb 100644
--- a/activesupport/lib/active_support/cache.rb
+++ b/activesupport/lib/active_support/cache.rb
@@ -1,7 +1,33 @@
 require 'benchmark'
 
 module ActiveSupport
+  # See ActiveSupport::Cache::Store for documentation.
   module Cache
+    # Creates a new CacheStore object according to the given options.
+    #
+    # If no arguments are passed to this method, then a new
+    # ActiveSupport::Cache::MemoryStore object will be returned.
+    #
+    # If you pass a Symbol as the first argument, then a corresponding cache
+    # store class under the ActiveSupport::Cache namespace will be created.
+    # For example:
+    #
+    #   ActiveSupport::Cache.lookup_store(:memory_store)
+    #   # => returns a new ActiveSupport::Cache::MemoryStore object
+    #   
+    #   ActiveSupport::Cache.lookup_store(:drb_store)
+    #   # => returns a new ActiveSupport::Cache::DRbStore object
+    #
+    # Any additional arguments will be passed to the corresponding cache store
+    # class's constructor:
+    #
+    #   ActiveSupport::Cache.lookup_store(:file_store, "/tmp/cache")
+    #   # => same as: ActiveSupport::Cache::FileStore.new("/tmp/cache")
+    #
+    # If the first argument is not a Symbol, then it will simply be returned:
+    #
+    #   ActiveSupport::Cache.lookup_store(MyOwnCacheStore.new)
+    #   # => returns MyOwnCacheStore.new
     def self.lookup_store(*store_option)
       store, *parameters = *([ store_option ].flatten)
 
@@ -36,6 +62,21 @@ module ActiveSupport
       expanded_cache_key
     end
 
+    # An abstract cache store class. There are multiple cache store
+    # implementations, each having its own additional features. See the classes
+    # under the ActiveSupport::Cache module, e.g.
+    # ActiveSupport::Cache::MemCacheStore. MemCacheStore is currently the most
+    # popular cache store for large production websites.
+    #
+    # ActiveSupport::Cache::Store is meant for caching strings. Some cache
+    # store implementations, like MemoryStore, are able to cache arbitrary
+    # Ruby objects, but don't count on every cache store to be able to do that.
+    #
+    #   cache = ActiveSupport::Cache::MemoryStore.new
+    #   
+    #   cache.read("city")   # => nil
+    #   cache.write("city", "Duckburgh")
+    #   cache.read("city")   # => "Duckburgh"
     class Store
       cattr_accessor :logger
 
@@ -44,7 +85,46 @@ module ActiveSupport
         self
       end
 
-      # Pass <tt>:force => true</tt> to force a cache miss.
+      # Fetches data from the cache, using the given key. If there is data in
+      # the cache with the given key, then that data is returned.
+      #
+      # If there is no such data in the cache (a cache miss occurred), then
+      # then nil will be returned. However, if a block has been passed, then
+      # that block will be run in the event of a cache miss. The return value
+      # of the block will be written to the cache under the given cache key,
+      # and that return value will be returned.
+      #
+      #   cache.write("today", "Monday")
+      #   cache.fetch("today")  # => "Monday"
+      #   
+      #   cache.fetch("city")   # => nil
+      #   cache.fetch("city") do
+      #     "Duckburgh"
+      #   end
+      #   cache.fetch("city")   # => "Duckburgh"
+      #
+      # You may also specify additional options via the +options+ argument.
+      # Setting <tt>:force => true</tt> will force a cache miss:
+      #
+      #   cache.write("today", "Monday")
+      #   cache.fetch("today", :force => true)  # => nil
+      #
+      # Other options will be handled by the specific cache store implementation.
+      # Internally, #fetch calls #read, and calls #write on a cache miss.
+      # +options+ will be passed to the #read and #write calls.
+      #
+      # For example, MemCacheStore's #write method supports the +:expires_in+
+      # option, which tells the memcached server to automatically expire the
+      # cache item after a certain period. We can use this option with #fetch
+      # too:
+      #
+      #   cache = ActiveSupport::Cache::MemCacheStore.new
+      #   cache.fetch("foo", :force => true, :expires_in => 5.seconds) do
+      #     "bar"
+      #   end
+      #   cache.fetch("foo")  # => "bar"
+      #   sleep(6)
+      #   cache.fetch("foo")  # => nil
       def fetch(key, options = {})
         @logger_off = true
         if !options[:force] && value = read(key, options)
@@ -68,10 +148,32 @@ module ActiveSupport
         end
       end
 
+      # Fetches data from the cache, using the given key. If there is data in
+      # the cache with the given key, then that data is returned. Otherwise,
+      # nil is returned.
+      #
+      # You may also specify additional options via the +options+ argument.
+      # The specific cache store implementation will decide what to do with
+      # +options+.
       def read(key, options = nil)
         log("read", key, options)
       end
 
+      # Writes the given value to the cache, with the given key.
+      #
+      # You may also specify additional options via the +options+ argument.
+      # The specific cache store implementation will decide what to do with
+      # +options+.
+      # 
+      # For example, MemCacheStore supports the +:expires_in+ option, which
+      # tells the memcached server to automatically expire the cache item after
+      # a certain period:
+      #
+      #   cache = ActiveSupport::Cache::MemCacheStore.new
+      #   cache.write("foo", "bar", :expires_in => 5.seconds)
+      #   cache.read("foo")  # => "bar"
+      #   sleep(6)
+      #   cache.read("foo")  # => nil
       def write(key, value, options = nil)
         log("write", key, options)
       end