module ActiveRecord # = Active Record Counter Cache module CounterCache # Resets one or more counter caches to their correct value using an SQL # count query. This is useful when adding new counter caches, or if the # counter has been corrupted or modified directly by SQL. # # ==== Parameters # # * +id+ - The id of the object you wish to reset a counter on. # * +counters+ - One or more counter names to reset # # ==== Examples # # # For Post with id #1 records reset the comments_count # Post.reset_counters(1, :comments) def reset_counters(id, *counters) object = find(id) counters.each do |association| has_many_association = reflect_on_association(association.to_sym) foreign_key = has_many_association.foreign_key.to_s child_class = has_many_association.klass belongs_to = child_class.reflect_on_all_associations(:belongs_to) reflection = belongs_to.find { |e| e.foreign_key.to_s == foreign_key } counter_name = reflection.counter_cache_column stmt = unscoped.where(arel_table[primary_key].eq(object.id)).arel.compile_update({ arel_table[counter_name] => object.send(association).count }) connection.update stmt end return true end # A generic "counter updater" implementation, intended primarily to be # used by increment_counter and decrement_counter, but which may also # be useful on its own. It simply does a direct SQL update for the record # with the given ID, altering the given hash of counters by the amount # given by the corresponding value: # # ==== Parameters # # * +id+ - The id of the object you wish to update a counter on or an Array of ids. # * +counters+ - An Array of Hashes containing the names of the fields # to update as keys and the amount to update the field by as values. # # ==== Examples # # # For the Post with id of 5, decrement the comment_count by 1, and # # increment the action_count by 1 # Post.update_counters 5, :comment_count => -1, :action_count => 1 # # Executes the following SQL: # # UPDATE posts # # SET comment_count = COALESCE(comment_count, 0) - 1, # # action_count = COALESCE(action_count, 0) + 1 # # WHERE id = 5 # # # For the Posts with id of 10 and 15, increment the comment_count by 1 # Post.update_counters [10, 15], :comment_count => 1 # # Executes the following SQL: # # UPDATE posts # # SET comment_count = COALESCE(comment_count, 0) + 1 # # WHERE id IN (10, 15) def update_counters(id, counters) updates = counters.map do |counter_name, value| operator = value < 0 ? '-' : '+' quoted_column = connection.quote_column_name(counter_name) "#{quoted_column} = COALESCE(#{quoted_column}, 0) #{operator} #{value.abs}" end IdentityMap.remove_by_id(symbolized_base_class, id) if IdentityMap.enabled? update_all(updates.join(', '), primary_key => id ) end # Increment a number field by one, usually representing a count. # # This is used for caching aggregate values, so that they don't need to be computed every time. # For example, a DiscussionBoard may cache post_count and comment_count otherwise every time the board is # shown it would have to run an SQL query to find how many posts and comments there are. # # ==== Parameters # # * +counter_name+ - The name of the field that should be incremented. # * +id+ - The id of the object that should be incremented. # # ==== Examples # # # Increment the post_count column for the record with an id of 5 # DiscussionBoard.increment_counter(:post_count, 5) def increment_counter(counter_name, id) update_counters(id, counter_name => 1) end # Decrement a number field by one, usually representing a count. # # This works the same as increment_counter but reduces the column value by 1 instead of increasing it. # # ==== Parameters # # * +counter_name+ - The name of the field that should be decremented. # * +id+ - The id of the object that should be decremented. # # ==== Examples # # # Decrement the post_count column for the record with an id of 5 # DiscussionBoard.decrement_counter(:post_count, 5) def decrement_counter(counter_name, id) update_counters(id, counter_name => -1) end end end