module ActiveRecord
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|
child_class = reflect_on_association(association).klass
counter_name = child_class.reflect_on_association(self.name.downcase.to_sym).counter_cache_column
connection.update("UPDATE #{quoted_table_name} SET #{connection.quote_column_name(counter_name)} = #{object.send(association).count} WHERE #{connection.quote_column_name(primary_key)} = #{quote_value(object.id)}", "#{name} UPDATE")
end
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 = comment_count - 1,
# # action_count = action_count + 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 = comment_count + 1,
# # WHERE id IN (10, 15)
def update_counters(id, counters)
updates = counters.inject([]) { |list, (counter_name, increment)|
sign = increment < 0 ? "-" : "+"
list << "#{connection.quote_column_name(counter_name)} = COALESCE(#{connection.quote_column_name(counter_name)}, 0) #{sign} #{increment.abs}"
}.join(", ")
if id.is_a?(Array)
ids_list = id.map {|i| quote_value(i)}.join(', ')
condition = "IN (#{ids_list})"
else
condition = "= #{quote_value(id)}"
end
update_all(updates, "#{connection.quote_column_name(primary_key)} #{condition}")
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
