我刚刚遇到了这样一个情况,我希望所有的JSON字段都是可选的(即用户可以选择是否填写),但在内部,如果用户没有指定某个字段,则所有字段都是非可选的,并具有精确定义的默认值。这与您的用例类似。
我目前正在考虑一种方法,即使用完全可选的参数来包装Foo
的构造:
case class Foo(id: Int, value: String, status: String)
object FooBuilder {
def apply(id: Option[Int], value: Option[String], status: Option[String]) = Foo(
id getOrElse 0,
value getOrElse "nothing",
status getOrElse "pending"
)
val fooReader: Reads[Foo] = (
(__ \ "id").readNullable[Int] and
(__ \ "value").readNullable[String] and
(__ \ "status").readNullable[String]
)(FooBuilder.apply _)
}
implicit val fooReader = FooBuilder.fooReader
val foo = Json.parse("""{"id": 1, "value": "foo"}""")
.validate[Foo]
.get
很不幸,这需要编写明确的Reads[Foo]
和Writes[Foo]
,这可能是您想避免的。另一个缺点是如果键丢失或值为null
,则默认值将仅被使用。然而,如果键包含错误类型的值,则整个验证会再次返回ValidationError
。
嵌套此类可选的JSON结构并不是问题,例如:
case class Bar(id1: Int, id2: Int)
object BarBuilder {
def apply(id1: Option[Int], id2: Option[Int]) = Bar(
id1 getOrElse 0,
id2 getOrElse 0
)
val reader: Reads[Bar] = (
(__ \ "id1").readNullable[Int] and
(__ \ "id2").readNullable[Int]
)(BarBuilder.apply _)
val writer: Writes[Bar] = (
(__ \ "id1").write[Int] and
(__ \ "id2").write[Int]
)(unlift(Bar.unapply))
}
case class Foo(id: Int, value: String, status: String, bar: Bar)
object FooBuilder {
implicit val barReader = BarBuilder.reader
implicit val barWriter = BarBuilder.writer
def apply(id: Option[Int], value: Option[String], status: Option[String], bar: Option[Bar]) = Foo(
id getOrElse 0,
value getOrElse "nothing",
status getOrElse "pending",
bar getOrElse BarBuilder.apply(None, None)
)
val reader: Reads[Foo] = (
(__ \ "id").readNullable[Int] and
(__ \ "value").readNullable[String] and
(__ \ "status").readNullable[String] and
(__ \ "bar").readNullable[Bar]
)(FooBuilder.apply _)
val writer: Writes[Foo] = (
(__ \ "id").write[Int] and
(__ \ "value").write[String] and
(__ \ "status").write[String] and
(__ \ "bar").write[Bar]
)(unlift(Foo.unapply))
}