--- /dev/null
+module ActiveRecord
+ module ConnectionAdapters # :nodoc:
+ module QueryCache
+ class << self
+ def included(base)
+ base.class_eval do
+ alias_method_chain :columns, :query_cache
+ alias_method_chain :select_all, :query_cache
+ end
+
+ dirties_query_cache base, :insert, :update, :delete
+ end
+
+ def dirties_query_cache(base, *method_names)
+ method_names.each do |method_name|
+ base.class_eval <<-end_code, __FILE__, __LINE__
+ def #{method_name}_with_query_dirty(*args)
+ clear_query_cache if @query_cache_enabled
+ #{method_name}_without_query_dirty(*args)
+ end
+
+ alias_method_chain :#{method_name}, :query_dirty
+ end_code
+ end
+ end
+ end
+
+ attr_reader :query_cache, :query_cache_enabled
+
+ # Enable the query cache within the block.
+ def cache
+ old, @query_cache_enabled = @query_cache_enabled, true
+ @query_cache ||= {}
+ yield
+ ensure
+ clear_query_cache
+ @query_cache_enabled = old
+ end
+
+ # Disable the query cache within the block.
+ def uncached
+ old, @query_cache_enabled = @query_cache_enabled, false
+ yield
+ ensure
+ @query_cache_enabled = old
+ end
+
+ # Clears the query cache.
+ #
+ # One reason you may wish to call this method explicitly is between queries
+ # that ask the database to randomize results. Otherwise the cache would see
+ # the same SQL query and repeatedly return the same result each time, silently
+ # undermining the randomness you were expecting.
+ def clear_query_cache
+ @query_cache.clear if @query_cache
+ end
+
+ def select_all_with_query_cache(*args)
+ if @query_cache_enabled
+ cache_sql(args.first) { select_all_without_query_cache(*args) }
+ else
+ select_all_without_query_cache(*args)
+ end
+ end
+
+ def columns_with_query_cache(*args)
+ if @query_cache_enabled
+ @query_cache["SHOW FIELDS FROM #{args.first}"] ||= columns_without_query_cache(*args)
+ else
+ columns_without_query_cache(*args)
+ end
+ end
+
+ private
+ def cache_sql(sql)
+ result =
+ if @query_cache.has_key?(sql)
+ log_info(sql, "CACHE", 0.0)
+ @query_cache[sql]
+ else
+ @query_cache[sql] = yield
+ end
+
+ if Array === result
+ result.collect { |row| row.dup }
+ else
+ result.duplicable? ? result.dup : result
+ end
+ rescue TypeError
+ result
+ end
+ end
+ end
+end