Decoding Fields 

instances of the trait DecodeBsonField are used to extract values from DBObject. various instances are already provided in DecodeBsonFields

import io.github.raptros.bson._
import scalaz.\/-
import Bson._ 

val dbo = DBO("int-key" :> 35)

val v = implicitly[DecodeBsonField[Int]].decode("int-key", dbo)
//alternatively
val v = implicitly[DecodeBsonField[Int]]("int-key", dbo)

v === \/-(35)

Extractor syntax 

The implicit class DBOWrapper is provided in Extractors; among others methods, it provides field.

val dbo = DBO("doubleKey" :> 33.2)

dbo.field[Double]("doubleKey")
v === \/-(33.2)

it also provides fieldOpt:

val dbo = DBO("k1": true)

val v0 = dbo.fieldOpt[Boolean]("k1")
v0 === \/-(Some(true))

val v1 = dbo.fieldOpt[Boolean]("k2")
v1 === \/-(None)

val v2 = dbo.fieldOpt[Double]("k1)
v2 === -\/(NonEmptyList(WrongFieldType("k1",
  classOf[java.lang.Double],
  classOf[java.lang.Boolean])))

Deriving new instances 

hopefully, you will not need to do this too often (for reasons explained in the next section), but there are several ways to derive new instances.

• you can transform successfully decoded values

  implicit val urlDecodeField: DecodeBsonField[URI] = 
    stringDecodeField map { s =>
      new URI(s) //pretend this works
    }
  

• you can use flatMap

• you can use orElse (aka |||), as used in the library itself

  implicit val datetimeDecodeField = 
    castableDecoder[DateTime] ||| 
    dateDecodeField map { d => new DateTime(d) }
  

• you can define new ones using the apply method in the DecodeBsonField object

  implicit def decodeOptionalField[A](implicit d: DecodeBsonField[A]): DecodeBsonField[Option[A]] = 
    DecodeBsonField { (k, dbo) =>
      if (dbo.containsField(k)) d(k, dbo) map { Some(_) } else none[A].right
    }