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

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  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) => icase None => -1}case Left(err) => -1}}val count: Int = Await.result(futCount, 2 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.globalimplicit 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) => icase None => -1}case Left(err) => -1}}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)}

现在我可以把代码简化成：

                val futSeqno = for {cnt <- repository.count(pid).toFuture_ <- addPicuture(pid, cnt, optDesc, optWid, optHgh, barr.toArray).toFuture} yield cnt

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).toFuturebarr <- futBytes_ <- addPicuture(pid, cnt, optDesc, optWid, optHgh, barr.toArray).toFuture} yield cntcomplete(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.DBOResultobject 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.globalimplicit 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.WebPicimport 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.globalvar 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 cntcomplete(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)).toFuturecomplete(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).toFutureonComplete(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 <- futbytesdoc = Document(bson) + ("photo" -> bytes.toArray)c <- repository.insert(doc).toFuture[Completed]} yield ccomplete(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.toval 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.toval futmsg = repository.replace(bson, doc).toFuturecomplete(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)}}}

 

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