I am using Scalatra, which in turn uses Json4S to generate Json string. I receive
["A","B"]
for
List(Some("A"),None,Some("B"))
I would like to receive
["A",undefined,"B"]
How can this be fixed ?
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Why do you want that undefined in there? How could the receiver of that information possible benefit from having an undefined in there vs just not having that element in the array?cmbaxter– cmbaxter2013-06-01 13:34:56 +00:00Commented Jun 1, 2013 at 13:34
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1When I serialise an array with 3 elements, I am expecting to receive a new array with 3 elements. Moreover: List(Some("A"),None,Some("B")) <> List(Some("A"),Some("B"),None) while the serialised arrays are equivalent !!! I reckon this is a bug in Json4S library.Ali Salehi– Ali Salehi2013-06-02 02:34:07 +00:00Commented Jun 2, 2013 at 2:34
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1 Answer
undefined is not a valid json value, even though it is valid in javascript.
From rfc4627 (application/json):
A JSON value MUST be an object, array, number, or string, or one of the following three literal names:
false null true
(no mention of undefined)
However this is fairly straight-forward to do with null instead of undefined. In the scala console, first a couple imports:
scala> import org.json4s._
scala> import org.json4s.native.Serialization.write
A customer serializer:
scala> class NoneJNullSerializer extends CustomSerializer[Option[_]](format => ({ case JNull => None }, { case None => JNull }))
And voila:
scala> implicit val formats = DefaultFormats + new NoneJNullSerializer()
scala> val ser = write(List(Some("A"), None, Some("B")))
ser: String = ["A",null,"B"]
3 Comments
Nick Mitchinson
This does not seem to solve the problem when the None is a value in a Map. The entire key seems to be stripped before the implicit conversion is hit.
theon
[edited] Whoops, forgot this was json4s and wrote a comment about spray-json :s
S.Karthik
This issue is solved in 3.2.11 version, you coud just use DefaultFormats.preservingEmptyValues. If anyone has issue, refer this stackoverflow.com/questions/27855934/…