Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (db *Database) FindRef(ref *DBRef) *Query {
	var c *Collection
	if ref.Database == "" {
		c = db.C(ref.Collection)
	} else {
		c = db.Session.DB(ref.Database).C(ref.Collection)
	}
	return c.FindId(ref.Id)
}
func (db *Database) FindRef(ref *DBRef) *Query {
	var c *Collection
	if ref.Database == "" {
		c = db.C(ref.Collection)
	} else {
		c = db.Session.DB(ref.Database).C(ref.Collection)
	}
	return c.FindId(ref.Id)
}
// NOTE: Order of fields for DBRef above does matter, per documentation.
// FindRef returns a query that looks for the document in the provided
// reference. If the reference includes the DB field, the document will
// be retrieved from the respective database.
//
// See also the DBRef type and the FindRef method on Session.
//
// Relevant documentation:
//
//     http://www.mongodb.org/display/DOCS/Database+References
//