Active Records support optimistic locking if the field lock_version is present. Each update to the record increments the lock_version column and the locking facilities ensure that records instantiated twice will let the last one saved raise a StaleObjectError if the first was also updated. Example:

p1 = Person.find(1)
p2 = Person.find(1)

p1.first_name = "Michael"
p1.save

p2.first_name = "should fail"
p2.save # Raises a ActiveRecord::StaleObjectError

You’re then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging, or otherwise apply the business logic needed to resolve the conflict.

You must ensure that your database schema defaults the lock_version column to 0.

This behavior can be turned off by setting ActiveRecord::Base.lock_optimistically = false. To override the name of the lock_version column, invoke the set_locking_column method. This method uses the same syntax as set_table_name

Namespace
Methods
A
Instance Public methods
attributes_from_column_definition_with_lock()

Source: show 

# File rails/activerecord/lib/active_record/locking/optimistic.rb, line 44
def attributes_from_column_definition_with_lock
  result = attributes_from_column_definition_without_lock
  
  # If the locking column has no default value set,
  # start the lock version at zero.  Note we can't use
  # locking_enabled? at this point as @attributes may
  # not have been initialized yet
  
  if lock_optimistically && result.include?(self.class.locking_column)
    result[self.class.locking_column] ||= 0
  end
  
  return result
end