Module: ActiveRecord::CounterCache::ClassMethods

Relationships & Source Files
Defined in:	activerecord/lib/active_record/counter_cache.rb

Instance Method Summary

#decrement_counter(counter_name, id)

Decrement a numeric field by one, via a direct SQL update.
#increment_counter(counter_name, id)

Increment a numeric field by one, via a direct SQL update.
#reset_counters(id, *counters)

Resets one or more counter caches to their correct value using an SQL count query.
#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.

Instance Method Details

#decrement_counter(counter_name, id)

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)

[ GitHub ]

# File 'activerecord/lib/active_record/counter_cache.rb', line 121


def decrement_counter(counter_name, id)
  update_counters(id, counter_name => -1)
end

#increment_counter(counter_name, id)

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)

[ GitHub ]

# File 'activerecord/lib/active_record/counter_cache.rb', line 103


def increment_counter(counter_name, id)
  update_counters(id, counter_name => 1)
end

#reset_counters(id, *counters)

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)

[ GitHub ]

# File 'activerecord/lib/active_record/counter_cache.rb', line 20


def reset_counters(id, *counters)
  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, "'#{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
    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

    stmt = unscoped.where(arel_table[primary_key].eq(object.id)).arel.compile_update({
      arel_table[counter_name] => object.send(counter_association).count(:all)
    }, primary_key)
    connection.update stmt
  end
  return 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.

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)

[ GitHub ]

# File 'activerecord/lib/active_record/counter_cache.rb', line 77


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