Default case class parameter with lift-json

Question

Basic scenario:

case class Something(
    date: Option[Date],
    timestamp: Option[Date] = Some(new Date)
);

class Users private() extends MongoRecord[Users] with ObjectIdPk[Users] {
    def meta = Users;
    object things extends MongoCaseClassListField[Users, Something](this);
};


object Users extends Users with MongoMetaRecord[Users] {

};     

def something(json: JValue) = {
    val something = json.extract[Something];// does not have a timestamp field.
    decompose(something); // again no timestamp field.
    Users.where(_.email eqs email).findAndModify(_.things addToSet something).updateOne(true);
};

Problem: When a JSON without a timestamp field is sent as a request, the database entry does not have a timestamp field at all.

If timestamp: Date instead of timestamp: Option[Date] is used, the JSON extraction throws a MappingException.

Q: How can a missing JSON field/case class param default to a value?

Answer 1

I would probably try something like this:

case class Something(date: Option[Date], timestamp: Option[Date]){
  def this(date:Option[Date]) = this(date, Some(new Date))
}

This creates a separate, one argument constructor and passes the default date to the two-argument constructor. Running it through REPL, you can see that the timestamp seems to get set correctly:

scala> parse(""" { "date":"2013-07-08T21:37:10Z" }  """)
res11: net.liftweb.json.JValue = JObject(List(JField(date,JString(2013-07-08T21:37:10Z))))

scala> res11.extract[Something]
res16: Something = Something(Some(Mon Jul 08 17:37:10 EDT 2013),Some(Mon Jul 08 17:43:52 EDT 2013))

scala> parse(""" {
     |   "date":"2013-07-08T21:37:10Z",
     |   "timestamp":"2013-07-08T21:37:10Z"
     | } """)
res14: net.liftweb.json.JValue = JObject(List(JField(date,JString(2013-07-08T21:37:10Z)), JField(timestamp,JString(2013-07-08T21:37:10Z))))

scala> res14.extract[Something]
res17: Something = Something(Some(Mon Jul 08 17:37:10 EDT 2013),Some(Mon Jul 08 17:37:10 EDT 2013))