如何分页外部调用，而反序列化Trait与类型参数使用喷雾?

Question

我有一个类似结构的对象，比如

case class Countries(countries: Array[Country])
case class Users(users: Array[User])
case class States(states: Array[States]) 

上面提到的类用于填充来自外部API调用的数据:

class GenericHttpDataPuller[U:JsonReader, V:JsonReader](val endPoint:String) {
def getEntity[T:JsonReader](request: HttpRequest): Option[T] = {
Try(httpClient.singleRequest(httpRequest).entity.parseJson.convertTo[T]) match 
{
case scala.util.Success(entityTry) => Some(entityTry)
case scala.util.Failure(exception) => None
}
}
def get(id:String, options: Map[String, String]): Option[U] = {
val uri = Uri(s"/$endPoint/$Id").withQuery(Uri.Query(queryMap.getOrElse(Map.empty[String,String])))
val httpRequest = HttpRequest(HttpMethods.GET,uri = uri,headers = additionalHeaders)
getEntity[U](httpRequest)
}
def getList(options: Map[String, String]): Option[V] = {
val uri = Uri(s"/$endPoint").withQuery(Uri.Query(queryMap.getOrElse(Map.empty[String,String])))
val httpRequest = HttpRequest(HttpMethods.GET,uri = uri,headers = additionalHeaders)
getEntity[V](httpRequest)
}
}

调用者

type HttpUserDataPuller = GenericHttpDataPuller[User, Users]
val users = new HttpUserDataPuller("users"). getList(None)
val user = new HttpUserDataPuller("users").get("someId", None)

上面的代码运行良好。

我想基于options参数对getList方法进行分页调用。我的修改与上面提到的代码不兼容，

trait Pagination[V, U] {
def getSize(): Int
def getAppend(u: Option[U]): Option[U]
}
case class Users(users: Array[User]) extends Pagination[User, Users] {
override def getSize(): Int = users.size
override def getAppend(u: Option[Users]): Option[Users] = { // u is the return value from getEntity()
val users = u.map(that => that.users ++ this.users).getOrElse(Array.empty[User])
Some(Users(users)) }
}

getList方法如下所示，使用getSize和getAppend方法，我可以根据getEntity[PaginationAppender]的返回类型计算是否要进行下一次调用(skip when getSize != current_page_size)，当我这样做时，我的代码中断，因为我无法使用Spary反序列化具有类型参数的trait。

def getList(options: Map[String, String]): Option[PaginationAppender[U, V]] = {
val limit = Try(queryMap.getOrElse(Map.empty[String, String]).getOrElse("limit", "-1").toInt).getOrElse(-1)
val uri = Uri(s"/$endPoint").withQuery(Uri.Query(queryMap.getOrElse(Map.empty[String,String])))
val httpRequest = HttpRequest(HttpMethods.GET,uri = uri,headers = additionalHeaders)
val returnValue = getEntity[PaginationAppender[U, V]]
def paginateData(currentPage: Option[PaginationAppender[U, V]]):Option[PaginationAppender[U, V]] = {
//page size is same as current request return value then go for next page
if(limit == currentPage.map(_.getSize()).getOrElse(0)) {
val nextPage = getEntity[PaginationAppender[U, V]](updatedRequsestForNextPage)
paginateData(currentPage.flatMap(now => now.append(nextPage)))
} else {
currentPage
}
paginateData(returnValue)
}

}

有没有更好的方法来解决这个问题，而不需要对现有的结构做太多的改变?

干杯! !

Answer 1

已使用的特性

trait PaginationAppender {
type T
def get(): Array[T]
}

由用户作为

实现

case class Users(users:Array[User]) extends PaginationAppender {
override type T = User
override def get(): Array[User] = this.users
}

标记方法

def paginateData[T:ClassTag, V <: PaginationAppender](httpUserDataPuller: GenericHttpDataPuller[T, V],
userId:String,
externalQueryMapOpt:Option[Map[String, String]] = None,
additionalHeaders:Option[Array[HttpHeader]] = None,
retry: Boolean = true,
limit: Int = 10,
offset: Int = 0
): ArraySeq[V#T] = {
val updatedExternalQueryMap = externalQueryMapOpt.getOrElse(Map.empty[String, String]) + ("limit" -> limit.toString) // add -OR- update limit to existing options
@tailrec
def getData(makeNextCall:Boolean, currentOffset: Int, existingData:  ArraySeq[V#T] = ArraySeq.empty[V#T]): ArraySeq[V#T] = {
makeNextCall match {
case true =>
val currentPage = httpUserDataPuller.list(Some(updatedExternalQueryMap + ("offset" -> currentOffset.toString)), // add -OR- update offset to existing options
userId,
additionalHeaders,
retry).getOrElse(throw new IllegalArgumentException(s"Failed to list from generic pagination")).get()
getData(currentPage.size == limit, currentOffset + limit, existingData ++ currentPage)
case false => existingData
}
}
getData(true, offset) //first time call
}

调用者

paginateData[User, Users](new HttpUserDataPuller("users"), "user")