key-value pair construction 

the tools to build DBObjects rely on DBOKV to write the key-value pairs into the objects. the implicit class StringToDBOKV provides methods for obtaining DBOKVs

val dbo = new BasicDBObject() //from the mongo-java-driver
val kv = "keyname" :> 25 //produces DBOKV[Int]("keyname", 25)
kv.write(dbo) //writes 25 into db at the key "keyname"

note that :> only produces a DBOKV if an implicit EncodeBsonField can be found for the type of the argument.

there are two different ways to write optional values.

• the first way relies on the instance for EncodeBsonField[Option[A]] in EncodeBsonFields

  val kv1: DBOKV[Option[Int]] = "keyname1" :> Some(25)
  kv1 === DBOKV("keyname1", Some(25))
  
  val kv2: DBOKV[Option[Int]] = "keyname2" :> (None: Option[Int])
  kv2 === DBOKV("keyname2", None)
  
  val dbo = DBO.empty
  kv1.write(dbo)
  kv2.write(dbo)
  
  kv1.keySet === Set("keyname1")
  kv1.get("keyname1") === 25
  

• the second uses a method in StringToDBOKV and uses the encoder for A directly:

  val kv1: Option[DBOKV[Int]] = "keyname1" :?> Some(25)
  kv1 === Some(DBOKV("keyname1", 25)
  
  val kv2: Option[DBOKV[Int]] = "keyname2" :?> None
  kv2 === None
  

  the utility of this method will be explained later