我正在尝试使用函数语法编写自定义json序列化程序,我似乎无法找到解决此特定问题的正确方法。我有几个joda DateTime对象,我想以特定的格式编写用于使用它的UI。有谁能告诉我哪里出错了?
这是我目前处理的案例类,没什么特别的。
case class Banner(
id: Int = 0,
ownerId: Int = 0,
licenseeId: Option[Int] = None,
statusColor: Option[String] = None,
content: Option[String] = None,
displayStart: DateTime = new DateTime(),
displayEnd: DateTime = new DateTime(),
created: DateTime = new DateTime(),
updated: DateTime = new DateTime()
)
这些是我对序列化程序对象的导入。
import play.api.libs.json._
import play.api.libs.functional.syntax._
import org.joda.time.DateTime
import org.joda.time.format.DateTimeFormat
首先,joda DateTime会隐式转换为long,因此如果我想要的话,宏扩展器的工作效果很好。
object MySerializers {
implicit val writesBanner = Json.writes[Banner]
}
我需要的是将displayStart和displayEnd对象转换为特定的字符串格式而不是long值。这就是我试图做的事情。
object MySerializers {
val userDateFormatter = DateTimeFormat.forPattern("MM/dd/yyyy HH:mm a")
implicit val writesBanner = (
(__ \ "id").write[Int] and
(__ \ "ownerId").write[Int] and
(__ \ "licenseeId").write[Int] and
(__ \ "statusColor").writeNullable[String] and
(__ \ "content").writeNullable[String] and
(__ \ "displayStart").write[DateTime].inmap[String](dt => userDateFormatter.print(dt)) and
(__ \ "displayEnd").write[DateTime].inmap[String](dt => userDateFormatter.print(dt)) and
(__ \ "created").write[DateTime] and
(__ \ "updated").write[DateTime]
)(unlift(Banner.unapply))
}
但编译器对此不满意,所以我似乎并不理解使用inmap函数的正确方法。
could not find implicit value for parameter fu:
play.api.libs.functional.InvariantFunctor[play.api.libs.json.OWrites]
[error] (__ \ "displayStart").write[DateTime].inmap[String](dt =>
userDateFormatter.print(dt)) and
[error] ^
非常感谢任何建议。
答案 0 :(得分:5)
我设法弄清楚了这一点,我使用了错误类型的仿函数地图操作,并且使用了我正在向后工作的类型。以下是更好的函数语法中的读/写实现。
implicit val writesBanner = (
(__ \ "id").write[Int] and
(__ \ "ownerId").write[Int] and
(__ \ "licenseeId").writeNullable[Int] and
(__ \ "statusColor").writeNullable[String] and
(__ \ "content").writeNullable[String] and
(__ \ "displayStart").write[String].contramap[DateTime](dt => userDateFormatter.print(dt)) and
(__ \ "displayEnd").write[String].contramap[DateTime](dt => userDateFormatter.print(dt)) and
(__ \ "created").write[DateTime] and
(__ \ "updated").write[DateTime]
)(unlift(Banner.unapply))
implicit val readsBanner = (
(__ \ "id").read[Int] and
(__ \ "ownerId").read[Int] and
(__ \ "licenseeId").readNullable[Int] and
(__ \ "statusColor").readNullable[String] and
(__ \ "content").readNullable[String] and
(__ \ "displayStart").read[String].fmap[DateTime](dt => DateTime.parse(dt, userDateFormatter)) and
(__ \ "displayEnd").read[String].fmap[DateTime](dt => DateTime.parse(dt, userDateFormatter)) and
(__ \ "created").read[DateTime] and
(__ \ "updated").read[DateTime]
)(Banner)
答案 1 :(得分:2)
我绝对不是这方面的专家,但我很确定你使用inmap的方式是你如何使用contramap / fmap的组合。
那是:
implicit val formatBanner = (
<truncated>
(__ \ "displayStart").format[String].inmap(DateTime.parse(_, userDateFormatter), userDateFormatter.print(_)) and
<truncated>
)(Banner.apply, unlift(Banner.unapply))