Possible Duplicate:
Why are exclamation marks used in Ruby methods?
i am reading tutorials for Rails3 with MongoDB
http://www.mongodb.org/display/DOCS/MongoDB+Data+Modeling+and+Rails
and i see this key :user_id, ObjectId timestamps! what does the exclamation mark mean??
Thanks.
class Story
include MongoMapper::Document
key :title, String
key :url, String
key :slug, String
key :voters, Array
key :votes, Integer, :default => 0
key :relevance, Integer, :default => 0
# Cached values.
key :comment_count, Integer, :default => 0
key :username, String
# Note this: ids are of class ObjectId.
key :user_id, ObjectId
timestamps!
# Relationships.
belongs_to :user
# Validations.
validates_presence_of :title, :url, :user_id
end