module IncrementWithSql

# File lib/increment_with_sql.rb, line 28
def decrement_with_sql!(attribute, by = 1)
  increment_with_sql! attribute, by * -1
end

# File lib/increment_with_sql.rb, line 9
def increment_with_sql!(attribute, by = 1)
  raise(NotPersistedError, "Record not persisted") if new_record?
  raise(InvalidAttributeError, "Invalid attribute #{attribute}") unless attribute_names.include?(attribute.to_s)

  self.class.transaction do
    self.class.where(:id => id).update_all("#{self.class.connection.quote_column_name attribute} = CASE WHEN #{self.class.connection.quote_column_name attribute} IS NULL THEN 0 ELSE #{self.class.connection.quote_column_name attribute} END + #{by.to_i}")

    send "#{attribute}=", self.class.unscoped.where(:id => id).select(attribute).first.send(attribute)

    if respond_to?(:clear_attribute_changes, true)
      send :clear_attribute_changes, [attribute]
    else
      changed_attributes.except! attribute.to_s
    end
  end 

  self
end