# File activerecord/lib/active_record/counter_cache.rb, line 156
def decrement_counter(counter_name, id, touch: nil)
  update_counters(id, counter_name => -1, touch: touch)
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.

• :touch - Touch timestamp columns when updating. Pass true to touch updated_at and/or updated_on. Pass a symbol to touch that column or an array of symbols to touch just those ones.

Examples

# Decrement the posts_count column for the record with an id of 5
DiscussionBoard.decrement_counter(:posts_count, 5)

# Decrement the posts_count column for the record with an id of 5
# and update the updated_at value.
DiscussionBoard.decrement_counter(:posts_count, 5, touch: true)

# File activerecord/lib/active_record/counter_cache.rb, line 131
def increment_counter(counter_name, id, touch: nil)
  update_counters(id, counter_name => 1, touch: touch)
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.

• :touch - Touch timestamp columns when updating. Pass true to touch updated_at and/or updated_on. Pass a symbol to touch that column or an array of symbols to touch just those ones.

Examples

# Increment the posts_count column for the record with an id of 5
DiscussionBoard.increment_counter(:posts_count, 5)

# Increment the posts_count column for the record with an id of 5
# and update the updated_at value.
DiscussionBoard.increment_counter(:posts_count, 5, touch: true)

# File activerecord/lib/active_record/counter_cache.rb, line 29
def reset_counters(id, *counters, touch: nil)
  object = find(id)

  counters.each do |counter_association|
    has_many_association = _reflect_on_association(counter_association)
    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, "'#{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
    reflection   = child_class._reflections.values.find { |e| e.belongs_to? && e.foreign_key.to_s == foreign_key && e.options[:counter_cache].present? }
    counter_name = reflection.counter_cache_column

    updates = { counter_name => object.send(counter_association).count(:all) }

    if touch
      names = touch if touch != true
      updates.merge!(touch_attributes_with_time(*names))
    end

    unscoped.where(primary_key => object.id).update_all(updates)
  end

  true
end

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.

• :touch - Touch timestamp columns when updating. Pass true to touch updated_at and/or updated_on. Pass a symbol to touch that column or an array of symbols to touch just those ones.

Examples

# For the Post with id #1, reset the comments_count
Post.reset_counters(1, :comments)

# Like above, but also touch the +updated_at+ and/or +updated_on+
# attributes.
Post.reset_counters(1, :comments, touch: true)

# File activerecord/lib/active_record/counter_cache.rb, line 104
def update_counters(id, counters)
  unscoped.where!(primary_key => id).update_counters(counters)
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.

• :touch option - Touch timestamp columns when updating. If attribute names are passed, they are updated along with updated_at/on attributes.

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)

# For the Posts with id of 10 and 15, increment the comment_count by 1
# and update the updated_at value for each counter.
Post.update_counters [10, 15], comment_count: 1, touch: true
# Executes the following SQL:
# UPDATE posts
#    SET comment_count = COALESCE(comment_count, 0) + 1,
#    `updated_at` = '2016-10-13T09:59:23-05:00'
#  WHERE id IN (10, 15)