search（4）- elastic4s-ElasticDsl

上次分析了一下elastic4s的运算框架。本来计划接着开始实质的函数调用示范，不过看过了Elastic4s的所有使用说明文档后感觉还是走的快了一点。主要原因是elasticsearch在7.0后有了很多重点调整改变，elastic4s虽然一直在源代码方面紧跟ES的变化，但使用文件却一直未能更新，所以从说明文档中学习elastic4s的使用方法是不可能的，必须从源码中摸索。花了些时间过了一次elastic4s的源码，感觉这个工具库以后还是挺有用的：一是通过编程方式产生json请求比较灵活，而且可以通过compiler来保证json语句的正确性。二是对搜索结果的处理方面：由于返回的搜索结果是一堆又长又乱的复杂json，不敢想象自己要如何正确的解析这些json, 然后才能调用到正确的结果，但elastic4s提供了一套很完善的response类，使用起来可能会很方便。实际上elastic4s的编程模式和scala语言运用还是值得学习的。既然这样，我想可能用elastic4s做一套完整的示范，包括：索引创建、索引维护、搜索、聚合统计等，对了解和掌握elastic4s可能大有帮助。在这之前，我们还是再回顾一下elastic4s的运算原理：elastic4s的功能其实很简单：通过dsl语句组合产生json请求，然后发送给ES-rest终端, 对返回的json结果进行处理，筛选出目标答案。

上篇我们讨论过elastic4s的基本运算框架：

  client.execute(
      createIndex("company")
      .shards().replicas()
  )

...

  val bookschema = putMapping("books")
      .as(
        KeywordField("isbn"),
        textField("title"),
        doubleField("price")
      )

  client.execute(
    bookschema
  )

...

  val futAccts = client.execute(
    search("bank").termQuery("city" -> "dante")
  )
  futAccts.onComplete{
    case Success(esresp) =>
      esresp.result.hits.hits.foreach(h =>println(h.sourceAsMap))
    case Failure(err) => println(s"search error: ${err.getMessage}")
  }

实际上execute(T)的T代表elastic4s支持的所有ES操作类型。这种方法实现有赖于scala的typeclass模式。我们先看看execute函数定义：

  // Executes the given request type T, and returns an effect of Response[U]
  // where U is particular to the request type.
  // For example a search request will return a Response[SearchResponse].
  def execute[T, U, F[_]](t: T)(implicit
                                executor: Executor[F],
                                functor: Functor[F],
                                handler: Handler[T, U],
                                manifest: Manifest[U]): F[Response[U]] = {
    val request = handler.build(t)
    val f = executor.exec(client, request)
    functor.map(f) { resp =>
      handler.responseHandler.handle(resp) match {
        case Right(u) => RequestSuccess(resp.statusCode, resp.entity.map(_.content), resp.headers, u)
        case Left(error) => RequestFailure(resp.statusCode, resp.entity.map(_.content), resp.headers, error)
      }
    }
  }

上篇提过Handler[T,U]是个typeclass, 代表对不同类型T的json构建方法。elastic4s提供了这个T类型的操作方法，如下：

trait ElasticDsl
    extends ElasticApi
    with Logging
    with ElasticImplicits
    with BulkHandlers
    with CatHandlers
    with CountHandlers
    with ClusterHandlers
    with DeleteHandlers
    with ExistsHandlers
    with ExplainHandlers
    with GetHandlers
    with IndexHandlers
    with IndexAdminHandlers
    with IndexAliasHandlers
    with IndexStatsHandlers
    with IndexTemplateHandlers
    with LocksHandlers
    with MappingHandlers
    with NodesHandlers
    with ReindexHandlers
    with RoleAdminHandlers
    with RoleHandlers
    with RolloverHandlers
    with SearchHandlers
    with SearchTemplateHandlers
    with SearchScrollHandlers
    with SettingsHandlers
    with SnapshotHandlers
    with UpdateHandlers
    with TaskHandlers
    with TermVectorHandlers
    with UserAdminHandlers
    with UserHandlers
    with ValidateHandlers {

  implicit class RichRequest[T](t: T) {
    def request(implicit handler: Handler[T, _]): ElasticRequest = handler.build(t)
    def show(implicit handler: Handler[T, _]): String            = Show[ElasticRequest].show(handler.build(t))
  }
}

object ElasticDsl extends ElasticDsl

所有的操作api在这里：

trait ElasticApi
  extends AliasesApi
    with ElasticImplicits
    with AggregationApi
    with AnalyzerApi
    with BulkApi
    with CatsApi
    with CreateIndexApi
    with ClearRolesCacheApi
    with ClusterApi
    with CollapseApi
    with CountApi
    with CreateRoleApi
    with CreateUserApi
    with DeleteApi
    with DeleteIndexApi
    with DeleteRoleApi
    with DeleteUserApi
    with DynamicTemplateApi
    with ExistsApi
    with ExplainApi
    with ForceMergeApi
    with GetApi
    with HighlightApi
    with IndexApi
    with IndexAdminApi
    with IndexRecoveryApi
    with IndexTemplateApi
    with LocksApi
    with MappingApi
    with NodesApi
    with NormalizerApi
    with QueryApi
    with PipelineAggregationApi
    with ReindexApi
    with RoleApi
    with ScriptApi
    with ScoreApi
    with ScrollApi
    with SearchApi
    with SearchTemplateApi
    with SettingsApi
    with SnapshotApi
    with SortApi
    with SuggestionApi
    with TaskApi
    with TermVectorApi
    with TokenizerApi
    with TokenFilterApi
    with TypesApi
    with UpdateApi
    with UserAdminApi
    with UserApi
    with ValidateApi {

  implicit class RichFuture[T](future: Future[T]) {
    def await(implicit duration: Duration = .seconds): T = Await.result(future, duration)
  }
}

object ElasticApi extends ElasticApi

通过 import ElasticDsl._  ，所有类型的api,handler操作方法都有了。下面是例子里的api方法：

trait CreateIndexApi {

  def createIndex(name: String): CreateIndexRequest = CreateIndexRequest(name)
...
}

trait MappingApi {
...
  def putMapping(indexes: Indexes): PutMappingRequest =  PutMappingRequest(IndexesAndType(indexes))
}

trait SearchApi {
  def search(index: String): SearchRequest = search(Indexes(index))
...
}

CreateIndexRequest, PutMappingRequest,SearchRequest这几个类型都提供了handler隐式实例：

trait IndexAdminHandlers {
...
  implicit object CreateIndexHandler extends Handler[CreateIndexRequest, CreateIndexResponse] {

    override def responseHandler: ResponseHandler[CreateIndexResponse] = new ResponseHandler[CreateIndexResponse] {
      override def handle(response: HttpResponse): Either[ElasticError, CreateIndexResponse] =
        response.statusCode match {
          case  |  => Right(ResponseHandler.fromResponse[CreateIndexResponse](response))
          case  |  => Left(ElasticError.parse(response))
          case _         => sys.error(response.toString)
        }
    }

    override def build(request: CreateIndexRequest): ElasticRequest = {

      val endpoint = "/" + URLEncoder.encode(request.name, "UTF-8")

      val params = scala.collection.mutable.Map.empty[String, Any]
      request.waitForActiveShards.foreach(params.put("wait_for_active_shards", _))
      request.includeTypeName.foreach(params.put("include_type_name", _))

      val body   = CreateIndexContentBuilder(request).string()
      val entity = HttpEntity(body, "application/json")

      ElasticRequest("PUT", endpoint, params.toMap, entity)
    }
  }

}

...

trait MappingHandlers {
...
 implicit object PutMappingHandler extends Handler[PutMappingRequest, PutMappingResponse] {

    override def build(request: PutMappingRequest): ElasticRequest = {

      val endpoint = s"/${request.indexesAndType.indexes.mkString(",")}/_mapping${request.indexesAndType.`type`.map("/" + _).getOrElse("")}"

      val params = scala.collection.mutable.Map.empty[String, Any]
      request.updateAllTypes.foreach(params.put("update_all_types", _))
      request.ignoreUnavailable.foreach(params.put("ignore_unavailable", _))
      request.allowNoIndices.foreach(params.put("allow_no_indices", _))
      request.expandWildcards.foreach(params.put("expand_wildcards", _))
      request.includeTypeName.foreach(params.put("include_type_name", _))

      val body   = PutMappingBuilderFn(request).string()
      val entity = HttpEntity(body, "application/json")

      ElasticRequest("PUT", endpoint, params.toMap, entity)
    }
  }

}
...
trait SearchHandlers {
...
  implicit object SearchHandler extends Handler[SearchRequest, SearchResponse] {

    override def build(request: SearchRequest): ElasticRequest = {

      val endpoint =
        if (request.indexes.values.isEmpty)
          "/_all/_search"
        else
          "/" + request.indexes.values
            .map(URLEncoder.encode(_, "UTF-8"))
            .mkString(",") + "/_search"

      val params = scala.collection.mutable.Map.empty[String, String]
      request.requestCache.map(_.toString).foreach(params.put("request_cache", _))
      request.searchType
        .filter(_ != SearchType.DEFAULT)
        .map(SearchTypeHttpParameters.convert)
        .foreach(params.put("search_type", _))
      request.routing.map(_.toString).foreach(params.put("routing", _))
      request.pref.foreach(params.put("preference", _))
      request.keepAlive.foreach(params.put("scroll", _))
      request.allowPartialSearchResults.map(_.toString).foreach(params.put("allow_partial_search_results", _))
      request.batchedReduceSize.map(_.toString).foreach(params.put("batched_reduce_size", _))

      request.indicesOptions.foreach { opts =>
        IndicesOptionsParams(opts).foreach { case (key, value) => params.put(key, value) }
      }

      request.typedKeys.map(_.toString).foreach(params.put("typed_keys", _))

      val body = request.source.getOrElse(SearchBodyBuilderFn(request).string())
      ElasticRequest("POST", endpoint, params.toMap, HttpEntity(body, "application/json"))
    }
  }

}