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module ActiveRecord
# = Active Record Counter Cache
module CounterCache
extend ActiveSupport::Concern
module ClassMethods
# 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 association counters to reset. Association name or counter name can be given.
#
# ==== 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 |counter_association|
has_many_association = reflect_on_association(counter_association.to_sym)
unless has_many_association
has_many = reflect_on_all_associations(:has_many)
has_many_association = has_many.find { |association| association.counter_cache_column && association.counter_cache_column.to_sym == counter_association.to_sym }
counter_association = has_many_association.plural_name if has_many_association
end
raise ArgumentError, "'#{self.name}' has no association called '#{counter_association}'" unless has_many_association
if has_many_association.is_a? ActiveRecord::Reflection::ThroughReflection
has_many_association = has_many_association.through_reflection
end
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 && e.options[:counter_cache].present? }
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(counter_association).count
}, primary_key)
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+ - A Hash 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
unscoped.where(primary_key => id).update_all updates.join(', ')
end
# Increment a numeric field by one, via a direct SQL update.
#
# This method is used primarily for maintaining counter_cache columns that are
# used to store aggregate values. For example, a DiscussionBoard may cache
# posts_count and comments_count to avoid running an SQL query to calculate the
# number of posts and comments there are, each time it is displayed.
#
# ==== Parameters
#
# * +counter_name+ - The name of the field that should be incremented.
# * +id+ - The id of the object that should be incremented or an Array of ids.
#
# ==== 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 numeric field by one, via a direct SQL update.
#
# 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 or an Array of ids.
#
# ==== 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
protected
def actually_destroyed?
@_actually_destroyed
end
def clear_destroy_state
@_actually_destroyed = nil
end
private
def _create_record(*)
id = super
each_counter_cached_associations do |association|
if send(association.reflection.name)
association.increment_counters
@_after_create_counter_called = true
end
end
id
end
def destroy_row
affected_rows = super
if affected_rows > 0
each_counter_cached_associations do |association|
foreign_key = association.reflection.foreign_key.to_sym
unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == foreign_key
if send(association.reflection.name)
association.decrement_counters
end
end
end
end
affected_rows
end
def each_counter_cached_associations
reflections.each do |name, reflection|
yield association(name) if reflection.belongs_to? && reflection.counter_cache_column
end
end
end
end
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