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
where(primary_key => id).update_all updates.join(', ')
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
