restapi（6）- do it the functional way, 重温函数式编程

再次看了看上篇博客的源代码，发现连自己都看不懂了。想是为了赶时间交货不知不觉又回到OOP行令模式了，看看下面这段代码：

       (post &  parameters('pid,'desc.?,'width.as[Int].?,'heigth.as[Int].?)) { (pid, optDesc, optWid, optHgh) =>
          val futCount: Future[Int] = repository.count(pid).value.value.runToFuture.map {
            eoi =>
              eoi match {
                case Right(oi) => oi match {
                  case Some(i) => i
                  case None => -
                }
                case Left(err) => -
              }
          }
          val count: Int = Await.result(futCount,  seconds)
          var doc = Document(
            "pid" -> pid,
            "seqno" -> count
          )
          if (optDesc != None)
            doc = doc + ("desc" -> optDesc.get)
          if (optWid != None)
            doc = doc + ("desc" -> optWid.get)
          if (optHgh != None)
            doc = doc + ("desc" -> optHgh.get)

          withoutSizeLimit {
            decodeRequest {
              extractDataBytes { bytes =>
                val fut = bytes.runFold(ByteString()) { case (hd, bs) =>
                  hd ++ bs
                }
                onComplete(fut) {
                  case Success(b) =>
                    doc = doc + ("pic" -> b.toArray)
                    val futmsg: Future[String] = repository.insert(doc).value.value.runToFuture.map {
                      eoc =>
                        eoc match {
                          case Right(oc) => oc match {
                            case Some(c) => count.toString //   c.toString()
                            case None => "insert may not complete!"
                          }
                          case Left(err) => err.getMessage
                        }
                    }
                    complete(futmsg)
                  case Failure(err) => complete(err)
                }
              }
            }
          }

有人能从这段代码里理解它的功能吗？本来作者的目的很简单：前端通过httprequest提交了一张图片及产品编号pid、系统读取MongoDB查找相同pid的数量count，然后将图片和描述包括count写入数据库并在reponse里返回count。把一个简单功能的实现搞的这么复杂都是我的错，可能受OOP荼毒太深。这次希望静下心来用函数式编程模式把这段代码从新实现一次，示范一下函数式编程的代码精炼和高雅特点。首先介绍一下DBResult[A]这个类型：这是一个Monad，为了应付Future[Either[Option[R]]]这样的类型而设计的，是一个表现数据库操作比较全面的类型，但同时它又是造成上面这段代码混乱的元凶。现在我们可以用隐式转换implicit conversion方式进行代码简化重用：

  import monix.execution.Scheduler.Implicits.global
  implicit class DBResultToFuture(dbr: DBOResult[_]){
      def toFuture[R] = {
        dbr.value.value.runToFuture.map {
          eor =>
            eor match {
              case Right(or) => or match {
                case Some(r) => r.asInstanceOf[R]
                case None => throw new RuntimeException("Operation produced None result!")
              }
              case Left(err) => throw new RuntimeException(err)
            }
        }
      }
  }

用这个隐式转换类型为任何DBOResult[R]增加一个函数toFuture[R]。现在整个futCount算式可以简化成下面这样：

          val futCount: Future[Int] = repository.count(pid).value.value.runToFuture.map {
            eoi =>
              eoi match {
                case Right(oi) => oi match {
                  case Some(i) => i
                  case None => -
                }
                case Left(err) => -
              }
          }

futCount:Future[Int]=repository.count(pid).toFuture

真正的简单易明。

不知怎么搞的，我尽然在这段代码中间使用了Await.result。从OOP角度分析这很容易理解，下一段程序需要上一段程序的结果来继续运行。在上面的例子里我们需要先获取count然后把count塞进Document再把Document存入数据库。逻辑思路上没问题，不过这样的做法是典型的行令式编程模式。在函数式编程模式里，阶段性的运算结果是在包嵌在Monad中的。Monad本身只是一个运算计划，只有真正运算时才能获取结果。Monad本身是函数组件，可以实现多个Monad的函数组合。在这里可以形象的把Monad函数组合描述为数据库操作步骤：先count、再insert，这两个步骤产生的结果还是留在Monad里的，直到所谓的世界末日，即实际运算完成后才取出，所以Monad是一种典型的程序运算流程管道。假如我们再把insert这段程序写成addPicture(...): DBOResult[_], 如下：

   def addPicuture(pid: String,seqno: Int, optDesc: Option[String]
                         ,optWid:Option[Int],optHgh:Option[Int],
                         bytes: Array[Byte]):DBOResult[Completed] ={
      var doc = Document(
        "pid" -> pid,
        "seqno" -> seqno,
        "pic" -> bytes
      )
      if (optDesc != None)
        doc = doc + ("desc" -> optDesc.get)
      if (optWid != None)
        doc = doc + ("desc" -> optWid.get)
      if (optHgh != None)
        doc = doc + ("desc" -> optHgh.get)
      repository.insert(doc)
    }

好了，现在整篇代码变成了下面这样：

       (post &  parameters('pid,'desc.?,'width.as[Int].?,'heigth.as[Int].?)) { (pid, optDesc, optWid, optHgh) =>
          withoutSizeLimit {
            decodeRequest {
              extractDataBytes { bytes =>
                val futBytes = bytes.runFold(ByteString()) { case (hd, bs) =>
                  hd ++ bs
                }
                val futSeqno = for {
                  cnt <- repository.count(pid).toFuture
                  barr <- futBytes
                  _ <- addPicuture(pid, cnt, optDesc, optWid, optHgh, barr.toArray).toFuture
                } yield cnt
                complete(futSeqno.map(_.toString))
              }
            }
  

现在是不是变得简单易明了？如果你觉着这样看起来更加容易理解，那么我建议你现在开始多点接触了解函数式编程。

接着用同样方式把整个项目重新实现一次。修改后的源代码如下：

MongoRepo.scala

package com.datatech.rest.mongo
import org.mongodb.scala._
import org.bson.conversions.Bson
import org.mongodb.scala.result._
import com.datatech.sdp.mongo.engine._
import MGOClasses._
import MGOEngine._
import MGOCommands._
import com.datatech.sdp.result.DBOResult.DBOResult

object MongoRepo {

  class MongoRepo[R](db:String, coll: String, converter: Option[Document => R])(implicit client: MongoClient) {
    def getAll[R](next:Option[String],sort:Option[String],fields:Option[String],top:Option[Int]): DBOResult[Seq[R]] = {
      var res = Seq[ResultOptions]()
      next.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_FILTER,Some(Document(b)))}
      sort.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_SORT,Some(Document(b)))}
      fields.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_PROJECTION,Some(Document(b)))}
      top.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_LIMIT,None,b)}

      val ctxFind = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_QUERY)
        .setCommand(Find(andThen = res))
      mgoQuery[Seq[R]](ctxFind,converter)
    }

    def query[R](filtr: Bson, next:Option[String]=None,sort:Option[String]=None,fields:Option[String]=None,top:Option[Int]=None): DBOResult[Seq[R]] = {
      var res = Seq[ResultOptions]()
      next.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_FILTER,Some(Document(b)))}
      sort.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_SORT,Some(Document(b)))}
      fields.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_PROJECTION,Some(Document(b)))}
      top.foreach {b => res = res :+ ResultOptions(FOD_TYPE.FOD_LIMIT,None,b)}
      val ctxFind = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_QUERY)
        .setCommand(Find(filter = Some(filtr),andThen = res))
      mgoQuery[Seq[R]](ctxFind,converter)
    }

    import org.mongodb.scala.model.Filters._
    def count(pid: String):DBOResult[Int] = {
      val ctxCount = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_QUERY)
        .setCommand(Count(filter=Some(equal("pid",pid))))
      mgoQuery[Int](ctxCount,None)
    }

    def getOneDocument(filtr: Bson): DBOResult[Document] = {
      val ctxFind = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_QUERY)
        .setCommand(Find(filter = Some(filtr),firstOnly = true))
      mgoQuery[Document](ctxFind,None)
    }
    def getOnePicture[R](pid: String, seqno: Int): DBOResult[R] = {
      val ctxFind = MGOContext(dbName = db, collName = coll)
        .setActionType(MGO_ACTION_TYPE.MGO_QUERY)
        .setCommand(Find(filter = Some(and(equal("pid",pid),equal("seqno",seqno))), firstOnly = true))
      mgoQuery[R](ctxFind, converter)
    }
    def insert(doc: Document): DBOResult[Completed] = {
      val ctxInsert = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_UPDATE)
        .setCommand(Insert(Seq(doc)))
      mgoUpdate[Completed](ctxInsert)
    }

    def delete(filter: Bson): DBOResult[DeleteResult] = {
      val ctxDelete = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_UPDATE)
        .setCommand(Delete(filter))
      mgoUpdate[DeleteResult](ctxDelete)
    }

    def update(filter: Bson, update: Bson, many: Boolean): DBOResult[UpdateResult] = {
      val ctxUpdate = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_UPDATE)
        .setCommand(Update(filter,update,None,!many))
      mgoUpdate[UpdateResult](ctxUpdate)
    }

    def replace(filter: Bson, row: Document): DBOResult[UpdateResult] = {
      val ctxUpdate = MGOContext(dbName = db,collName=coll)
        .setActionType(MGO_ACTION_TYPE.MGO_UPDATE)
        .setCommand(Replace(filter,row))
      mgoUpdate[UpdateResult](ctxUpdate)
    }

  }
  import monix.execution.Scheduler.Implicits.global
  implicit class DBResultToFuture(dbr: DBOResult[_]){
      def toFuture[R] = {
        dbr.value.value.runToFuture.map {
          eor =>
            eor match {
              case Right(or) => or match {
                case Some(r) => r.asInstanceOf[R]
                case None => throw new RuntimeException("Operation produced None result!")
              }
              case Left(err) => throw new RuntimeException(err)
            }
        }
      }
  }

}

MongoRoute.scala

package com.datatech.rest.mongo
import akka.http.scaladsl.server.Directives
import com.datatech.sdp.file._

import scala.util._
import org.mongodb.scala._
import com.datatech.sdp.file.Streaming._
import org.mongodb.scala.result._
import MongoRepo._
import akka.stream.ActorMaterializer
import com.datatech.sdp.result.DBOResult._
import org.mongodb.scala.model.Filters._
import com.datatech.sdp.mongo.engine.MGOClasses._
import monix.execution.CancelableFuture
import akka.util._
import akka.http.scaladsl.model._
import akka.http.scaladsl.coding.Gzip
import akka.stream.scaladsl._
import MongoModels.WebPic

import scala.concurrent._
import scala.concurrent.duration._
object MongoRoute {
  class MongoRoute[M <: ModelBase[Document]](val pathName: String)(repository: MongoRepo[M])(
    implicit c: MongoClient, m: Manifest[M], mat: ActorMaterializer) extends Directives with JsonConverter {
    import monix.execution.Scheduler.Implicits.global
    var dbor: DBOResult[Seq[M]] = _
    var dbou: DBOResult[UpdateResult] = _
    val route = pathPrefix(pathName) {
      pathPrefix("pictures") {
        (post &  parameters('pid,'desc.?,'width.as[Int].?,'heigth.as[Int].?)) { (pid, optDesc, optWid, optHgh) =>
          withoutSizeLimit {
            decodeRequest {
              extractDataBytes { bytes =>
                val futBytes = bytes.runFold(ByteString()) { case (hd, bs) =>
                  hd ++ bs
                }
                val futSeqno = for {
                  cnt <- repository.count(pid).toFuture[Int]
                  barr <- futBytes
                  _ <- addPicuture(pid, cnt, optDesc, optWid, optHgh, barr.toArray).toFuture[Completed]
                } yield cnt
                complete(futSeqno.map(_.toString))
              }
            }
          } ~
            (get & parameters('pid, 'seqno.as[Int].?, 'width.as[Int].?, 'height.as[Int].?)) {
              (pid, optSeq, optWid, optHght) =>
                if (optSeq == None) {
                  val futRows = repository.query(equal("pid", pid)).toFuture
                  complete(futureToJson(futRows))
                } else {
                  val futPicRow = repository.getOnePicture(pid, optSeq.get).toFuture[WebPic]
                  onComplete(futPicRow) {
                    case Success(row) =>
                      val width = if (optWid == None) row.width.getOrElse(128) else optWid.getOrElse(128)
                      val height = if (optHght == None) row.heigth.getOrElse(128) else optHght.getOrElse(128)
                      if (row.pic != None) {
                        withoutSizeLimit {
                          encodeResponseWith(Gzip) {
                            complete(
                              HttpEntity(
                                ContentTypes.`application/octet-stream`,
                                ByteArrayToSource(Imaging.setImageSize(row.pic.get.getData, width, height)
                                ))
                            )
                          }
                        }
                      } else complete(StatusCodes.NotFound)
                    case Failure(err) => complete(err)
                  }
                }
            }
        }
      } ~
        pathPrefix("blob") {
          (get & parameter('filter)) { filter =>
            val filtr = Document(filter)
            val futOptPic: CancelableFuture[Option[MGOBlob]] = repository.getOneDocument(filtr).toFuture
            onComplete(futOptPic) {
              case Success(optBlob) => optBlob match {
                case Some(blob) =>
                  withoutSizeLimit {
                    encodeResponseWith(Gzip) {
                      complete(
                        HttpEntity(
                          ContentTypes.`application/octet-stream`,
                          ByteArrayToSource(blob.getData)
                        )
                      )
                    }
                  }
                case None => complete(StatusCodes.NotFound)
              }
              case Failure(err) => complete(err)
            }
          } ~
            (post &  parameter('bson)) { bson =>
              val bdoc = Document(bson)
              withoutSizeLimit {
                decodeRequest {
                  extractDataBytes { bytes =>
                    val futbytes = bytes.runFold(ByteString()) { case (hd, bs) =>
                      hd ++ bs
                    }
                    val futmsg:Future[Completed] = for {
                      bytes <- futbytes
                      doc = Document(bson) + ("photo" -> bytes.toArray)
                      c <- repository.insert(doc).toFuture[Completed]
                    } yield c
                    complete(futmsg.map(_.toString))
                  }
                }
              }
            }
        } ~
        (get & parameters('filter.?,'fields.?,'sort.?,'top.as[Int].?,'next.?)) {
          (filter,fields,sort,top,next) => {
            dbor = {
              filter match {
                case Some(fltr) => repository.query(Document(fltr),next,sort,fields,top)
                case None => repository.getAll(next,sort,fields,top)
              }
            }
            val futRows:Future[Seq[WebPic]] = dbor.toFuture[Seq[WebPic]]
            complete(futureToJson(futRows))
          }
        } ~ post {
        entity(as[String]) { json =>
          val extractedEntity: M = fromJson[M](json)
          val doc: Document = extractedEntity.to
          val futmsg = repository.insert(doc).toFuture[Completed]
          complete(futmsg.map(_.toString))
        }
      } ~ (put & parameter('filter,'set.?, 'many.as[Boolean].?)) { (filter, set, many) =>
        val bson = Document(filter)
        if (set == None) {
          entity(as[String]) { json =>
            val extractedEntity: M = fromJson[M](json)
            val doc: Document = extractedEntity.to
            val futmsg = repository.replace(bson, doc).toFuture
            complete(futureToJson(futmsg))
          }
        } else {
          set match {
            case Some(u) =>
              val ubson = Document(u)
              dbou = repository.update(bson, ubson, many.getOrElse(true))
            case None =>
              dbou = Left(new IllegalArgumentException("missing set statement for update!"))
          }
          val futmsg:Future[UpdateResult] = dbou.toFuture[UpdateResult]
          complete(futureToJson(futmsg.map(_.toString)))
        }
      } ~ (delete & parameters('filter, 'many.as[Boolean].?)) { (filter,many) =>
        val bson = Document(filter)
        val futmsg:Future[DeleteResult] = repository.delete(bson).toFuture[DeleteResult]
        complete(futureToJson(futmsg.map(_.toString)))
      }
    }

    def addPicuture(pid: String,seqno: Int, optDesc: Option[String]
                         ,optWid:Option[Int],optHgh:Option[Int],
                         bytes: Array[Byte]):DBOResult[Completed] ={
      var doc = Document(
        "pid" -> pid,
        "seqno" -> seqno,
        "pic" -> bytes
      )
      if (optDesc != None)
        doc = doc + ("desc" -> optDesc.get)
      if (optWid != None)
        doc = doc + ("desc" -> optWid.get)
      if (optHgh != None)
        doc = doc + ("desc" -> optHgh.get)
      repository.insert(doc)
    }

  }

}