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module ActiveRecord::CounterCache::ClassMethods

Public instance methods

decrement_counter(counter_name, id, by: 1, touch: nil)

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.

  • :by - The amount by which to decrement the value. Defaults to 1.

  • :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
by a specific amount.
DiscussionBoard.decrement_counter(:posts_count, 5, by: 3)

# 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)
Source code GitHub 
# File activerecord/lib/active_record/counter_cache.rb, line 203
def decrement_counter(counter_name, id, by: 1, touch: nil)
  update_counters(id, counter_name => -by, touch: touch)
end

increment_counter(counter_name, id, by: 1, touch: nil)

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.

  • :by - The amount by which to increment the value. Defaults to 1.

  • :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
# by a specific amount.
DiscussionBoard.increment_counter(:posts_count, 5, by: 3)

# 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)
Source code GitHub 
# File activerecord/lib/active_record/counter_cache.rb, line 173
def increment_counter(counter_name, id, by: 1, touch: nil)
  update_counters(id, counter_name => by, touch: touch)
end

reset_counters(id, *counters, touch: nil)

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 or an array of ids.

  • 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)

# For posts with ids #1 and #2, reset the comments_count
Post.reset_counters([1, 2], :comments)

# Like above, but also touch the +updated_at+ and/or +updated_on+
# attributes.
Post.reset_counters(1, :comments, touch: true)
Source code GitHub 
# File activerecord/lib/active_record/counter_cache.rb, line 37
def reset_counters(id, *counters, touch: nil)
  ids = if composite_primary_key?
    if id.first.is_a?(Array)
      id
    else
      [id]
    end
  else
    Array(id)
  end

  updates = Hash.new { |h, k| h[k] = {} }

  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

    counter_association = counter_association.to_sym
    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

    counts =
      unscoped
        .joins(counter_association)
        .where(primary_key => ids)
        .group(primary_key)
        .count(:all)

    ids.each do |id|
      updates[id].merge!(counter_name => counts[id] || 0)
    end
  end

  if touch
    names = touch if touch != true
    names = Array.wrap(names)
    options = names.extract_options!
    touch_updates = touch_attributes_with_time(*names, **options)

    updates.each_value do |record_updates|
      record_updates.merge!(touch_updates)
    end
  end

  updates.each do |id, record_updates|
    unscoped.where(primary_key => [id]).update_all(record_updates)
  end

  true
end

update_counters(id, counters)

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 comments_count by 1, and
# increment the actions_count by 1
Post.update_counters 5, comments_count: -1, actions_count: 1
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) - 1,
#        actions_count = COALESCE(actions_count, 0) + 1
#  WHERE id = 5

# For the Posts with id of 10 and 15, increment the comments_count by 1
Post.update_counters [10, 15], comments_count: 1
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) + 1
#  WHERE id IN (10, 15)

# For the Posts with id of 10 and 15, increment the comments_count by 1
# and update the updated_at value for each counter.
Post.update_counters [10, 15], comments_count: 1, touch: true
# Executes the following SQL:
# UPDATE posts
#    SET comments_count = COALESCE(comments_count, 0) + 1,
#    `updated_at` = '2016-10-13T09:59:23-05:00'
#  WHERE id IN (10, 15)
Source code GitHub 
# File activerecord/lib/active_record/counter_cache.rb, line 140
def update_counters(id, counters)
  id = [id] if composite_primary_key? && id.is_a?(Array) && !id[0].is_a?(Array)
  unscoped.where!(primary_key => id).update_counters(counters)
end

Definition files