Mongoid document Time to Live

Question

Is there a way to set time to live for a document and then it gets destroyed. I want to create guest users that are temporary per session, so after a week the document gets removed automatically.

Answer 1

MongoDB (version 2.2 and up) actually has a special index type that allows you to specify a TTL on a document (see http://docs.mongodb.org/manual/tutorial/expire-data/). The database removes expired documents for you--no need for cron jobs or anything.

Mongoid supports this feature as follows:

index({created_at: 1}, {expire_after_seconds: 1.week})

The created_at field must hold date/time information. Include Mongoid::Timestamps in your model to get that for free.

UPDATE:

If you want to expire only a subset of documents, then you can create a special date/time field that is only populated for that subset. Documents with no value or a non-date/time value in the indexed field will never expire. For example:

# Special date/time field to base expirations on.
field :expirable_created_at, type: Time

# TTL index on the above field.
index({expirable_created_at: 1}, {expire_after_seconds: 1.week})

# Callback to set `expirable_created_at` only for guest roles.
before_create :set_expire, if: "role == :guest"
def set_expire
  self.expirable_created_at = Time.now
  return true
end