import "gopkg.in/mgo.v2/bson" // Creating a new ObjectId oid := bson.NewObjectId() // Converting a string to an ObjectId id := "5a4aeb41c4966c0014fd8a30" oid := bson.ObjectIdHex(id) // Converting an ObjectId to a string str := oid.Hex()In the first example, a new ObjectId is created using the bson.NewObjectId() function. This is useful when creating a new document that needs a unique identifier. In the second example, a string representing an ObjectId is converted into an actual ObjectId using the bson.ObjectIdHex() function. This is useful when retrieving a document by its unique identifier. In the third example, an ObjectId is converted into a string using the Hex() method. This is useful when displaying the ObjectId in a user interface or logging it for debugging purposes. Overall, the gopkg.in.mgo.v2.bson package library is a useful tool for working with MongoDB databases in Go, providing convenient functionality for encoding and decoding BSON documents and managing unique identifiers.