Scala object to Json Formatter using combinators

Question

I have implemented a class following Scala documentation

case class Creature(
  name: String, 
  isDead: Boolean, 
  weight: Float,
  dob: java.sql.Date
)

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val creatureFormat = (
  (__ \ "name").format[String] and
  (__ \ "isDead").format[Boolean] and
  (__ \ "weight").format[Float] and
  (__ \ "dob").format[java.sql.Date]
)(Creature.apply, unlift(Creature.unapply))

Then I call the json wrapper like this Json.toJson(Creature("John Doe", false, 100.0, new java.sql.Date(1363456800000))) and expect to see an output like {"name": "John Doe", "isDead": false, "weight": 100.0, "dob": "2013-03-17"}. Instead, I am getting an output like {"name": "John Doe", "isDead": false, "weight": 100.0, "dob": 1363456800000}.

Please note that, in the database, I can see the dob as 2013-03-17.

Julien Richard-Foy · Accepted Answer · 2013-05-15 10:20:44Z

1

By default the java.util.Date Json serializer produces a number containing the date timestamp.

Alternatively, you can use a date serializer that produces a String containing a representation of the date. However, because there is no standard representation of dates in JSON, you have to explicitly supply the pattern to use to produce the text representation:

implicit val creatureFormat = (
  (__ \ "name").format[String] and
  (__ \ "isDead").format[Boolean] and
  (__ \ "weight").format[Float] and
  (__ \ "dob").format(sqlDateWrites("YYYY-MM-DD"))(sqlDateReads("YYYY-MM-DD"))
)(Creature.apply, unlift(Creature.unapply))

answered May 15, 2013 at 10:20

Julien Richard-Foy

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2 Comments

Khalid Saifullah Over a year ago

Thanks a lot for the insight. Problem with this approach is that, if I have several SQL Date fields in my model/class, I will need to implement the formatter for all the Date fields. The problem furthers for the fact, in most real project, there will be many models/class with many date fields. I am not a self-righteous person, but I still think that I need to define the SQL date formatter once so that any model can use that serializer.

Julien Richard-Foy Over a year ago

You can define it once: val sqlDateFormat = Format(sqlDateReads("YYYY-MM-DD"), sqlDateWrites("YYYY-MM-DD")). And then (__ \ "dob").format(sqlDateFormat). You can even declare sqlDateFormat as an implicit value and import it in your other format definitions, so it will be automatically used if you write ( (__ \ "dob").format[java.sql.Date]

Khalid Saifullah · Accepted Answer · 2013-05-18 05:07:52Z

1

Here's how I resolved it (I explicitly defined apply and unapply methods)

val sdf = new java.text.SimpleDateFormat("yyyy-MM-dd")
implicit val creatureFormat = (
  (__ \ "name").format[String] and
  (__ \ "isDead").format[Boolean] and
  (__ \ "weight").format[Float] and
  (__ \ "dob").format[String])
    (((name, isDead, weight, dob) => Creature(name, isDead, weight, new java.sql.Date(sdf.parse(dob).getTime()))),
    unlift((cr: Creature) => Some(cr.name, cr.isDead, cr.weight, sdf.format(cr.dob))))

I do not know whether there is any better solutions.

Update

Finally, I implemented a formatter for java.sql.Date

import play.api.libs.json._
import play.api.libs.functional.syntax._
import play.api.data.validation.ValidationError
import play.api.libs.json.{ Json => PlayJson, _ }

case class Creature(
  name: String, 
  isDead: Boolean, 
  weight: Float,
  dob: java.sql.Date
)

implicit val sqlDateWrite = new Format[SqlDate] {
  def reads(json: JsValue) = json match {
    case JsString(d) => {
      val theDate = new SqlDate(sdf.parse(d).getTime)
      if (d.matches(sdfPattern) && theDate.compareTo(new Date(0)) > 0) JsSuccess(new SqlDate(sdf.parse(d).getTime))
      else JsError(Seq(JsPath() -> Seq(ValidationError("validate.error.expected.date.in.format(dd-MM-yyyy)"))))
    }
    case _ => JsError(Seq(JsPath() -> Seq(ValidationError("validate.error.expected.date.in.String"))))
  }

  def writes(sd: SqlDate): JsValue = JsString(sdf.format(sd))
}

implicit val creatureFormat = PlayJson.format[Creature]

Now, both these lines works

val mcJson = PlayJson.toJson(Creature("John Doe", false, 100, new SqlDate(1368430000000L)))
val mcObj = PlayJson.fromJson[Creature](PlayJson.obj("name"-> "Abul Khan", "isDead"-> true, "weight"-> 115, "dob"-> "17-05-2011")).getOrElse(null)

edited May 18, 2013 at 5:07

answered May 7, 2013 at 11:32

Khalid Saifullah

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3 Comments

Julien Lafont Over a year ago

There is a better solution :) I'll post it asap. In resume, define your own java.sql.Date writer

Khalid Saifullah Over a year ago

@JulienLafont Did you get time to prepare the better solution? Thanks in anticipation.

Khalid Saifullah Over a year ago

I forgot the date patterns

val sdfPattern = "\\b(0[1-9]|[1-3][0-9])-(0[1-9]|1[0-2])-[1-9][0-9]{3}\\b" val dtFmt = new java.text.SimpleDateFormat("dd-MM-yyyy", java.util.Locale.ENGLISH)

korefn · Accepted Answer · 2013-05-07 10:48:52Z

0

Since you expect strings you'd have to convert everything to string and lose typing.

Json.toJson(
  Creature(
    "John Doe", "false", "100.0",(new java.sql.Date(1363456800000)).toString
  )
)

answered May 7, 2013 at 10:48

korefn

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2 Comments

Khalid Saifullah Over a year ago

Did you really try with your own code? Please notice my Creature class and the data types of its attribs. I cannot convert every params to String, that way I will lose my original object. Thanks anyway for your thoughts.

korefn Over a year ago

Apologies. You can use unapply to do this. Since the data types have toString methods defined. You can implement unapply to convert every field to string while unboxing.

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