Nullablle support in Scala - scala

Question

Can I have Nullable parameters in Scala object.
Similar to Nullable in C# and the syntactic sugar:
public int? Age {get; set;}
public string Name {get; set;}
public bool? isAdmin {get; set;}
Can I create scala class where the object can have some of these attributes set while others not?
I intend to have multiple constructors for different purposes. I want to ensure a null value implies the field is not set.
UPDATE
for example I have the following case class
case class Employee(age: Int, salary: Int, scaleNum : Int,
name: String, memberId: Int )
I am using GSON to serialize the class in JSON.
In some cases however, I don't want to pass values for some of the parameters such that the GSON serializer will only include the parameters that have non-NULL value.
How can I achieve that with Options or otherwise?

Answer 1

A common declaration in Scala for your example would be:
case class Employee(
age: Option[Int], // For int? Age
name: String // For string Name
// your other decls ...
)
Then you can use the type easily:
val john = Employee( age = Some(10), name = "John" )
While Scala 2 allows null values for references types (like String, etc) it is slowly changing starting with Scala 3 (https://dotty.epfl.ch/docs/reference/other-new-features/explicit-nulls.html).
JSON support
Java libraries (like GSON) don't know anything about Scala, so you should consider using other libraries for JSON support that support Scala:
circe
play json
jsoniter-scala
uPickle
etc
Those libraries not just aware of Option[] in your class definitions, but also have improved support for Scala collections, implicits, default values and other Scala language features.
It is really important to choose an appropriate library for this, because with the Java JSON libs you will end up with Java-style classes and code, compatibility issues with other Scala libs.
With the Circe your example would be:
import io.circe._
import io.circe.syntax._
import io.circe.parser._
import io.circe.generic.auto._
val john = Employee( age = Some(10), name = "John" )
val johnAsJson = john.asJson.dropNullValues
decode[Employee]( johnAsJson ) match {
case Right(johnBack) => ??? // johnBack now is the same as john
case Left(err) => ??? // handle JSON parse exceptions
}
Null coalescing operator
Now you might be looking where is the Null Coalescing Operator (?? in C#, ? in Kotlin, ...) in Scala.
The direct answer - there is none in the language itself. In Scala we work with Option (and other monadic structures, or ADT) in FP way.
That means, for example:
case class Address(zip : Option[String])
case class Employee(
address: Option[Address]
)
val john = Employee( address = Some( Address( zip = Some("1111A") )) )
you should avoid this style:
if (john.address.isDefined) {
if(john.address.zip.isDefined) {
...
}
}
you can use map/flatMaps instead:
john.address.flatMap { address =>
address.zip.map { zip =>
// your zip and address value
??
}
}
// or if you need only zip in a short form:
john.address.flatMap(_.zip).map { zip =>
// your zip value
??
}
or for-comprehension syntax (which is based on the same flatMaps):
for {
address <- john.address
zip <- address.zip
}
yield {
// doing something with zip and address
??
}
The important part is that idiomatic way to solve this in Scala mostly based on patterns from FP.