(api): Support k-nearest neighbor (kNN) search

.github/workflows/ci.yml

@@ -38,7 +38,6 @@ jobs:
       matrix:
         java: [ "11", "17" ]
         scala: [ "2.12.18", "2.13.12", "3.3.1" ]
-        elasticsearch: ["7.x", "8.x"]
     steps:
       - name: Checkout current branch
         uses: actions/checkout@v4.1.1
@@ -55,7 +54,7 @@ jobs:
       - name: Run tests
         run: ./sbt ++${{ matrix.scala }}! library/test
       - name: Run test container
-        run: docker-compose -f docker/elasticsearch-${{ matrix.elasticsearch }}.yml up -d
+        run: docker-compose -f docker/elasticsearch-8.x.yml up -d
       - name: Run integration tests
         run: ./sbt ++${{ matrix.scala }}! integration/test
 

modules/integration/src/test/scala/zio/elasticsearch/HttpExecutorSpec.scala

@@ -1049,6 +1049,61 @@ object HttpExecutorSpec extends IntegrationSpec {
             Executor.execute(ElasticRequest.deleteIndex(firstSearchIndex)).orDie
           )
         ),
+        suite("kNN search")(
+          test("search for top two results") {
+            checkOnce(genDocumentId, genTestDocument, genDocumentId, genTestDocument, genDocumentId, genTestDocument) {
+              (firstDocumentId, firstDocument, secondDocumentId, secondDocument, thirdDocumentId, thirdDocument) =>
+                for {
+                  _                    <- Executor.execute(ElasticRequest.deleteByQuery(firstSearchIndex, matchAll))
+                  firstDocumentUpdated  = firstDocument.copy(vectorField = List(1, 5, -20))
+                  secondDocumentUpdated = secondDocument.copy(vectorField = List(42, 8, -15))
+                  thirdDocumentUpdated  = thirdDocument.copy(vectorField = List(15, 11, 23))
+                  req1                  = ElasticRequest.create(firstSearchIndex, firstDocumentId, firstDocumentUpdated)
+                  req2                  = ElasticRequest.create(firstSearchIndex, secondDocumentId, secondDocumentUpdated)
+                  req3                  = ElasticRequest.create(firstSearchIndex, thirdDocumentId, thirdDocumentUpdated)
+                  _                    <- Executor.execute(ElasticRequest.bulk(req1, req2, req3).refreshTrue)
+                  query                 = ElasticQuery.kNN(TestDocument.vectorField, 2, 3, Chunk(-5.0, 9.0, -12.0))
+                  res                  <- Executor.execute(ElasticRequest.knnSearch(firstSearchIndex, query)).documentAs[TestDocument]
+                } yield (assert(res)(equalTo(Chunk(firstDocumentUpdated, thirdDocumentUpdated))))
+            }
+          } @@ around(
+            Executor.execute(
+              ElasticRequest.createIndex(
+                firstSearchIndex,
+                """{ "mappings": { "properties": { "vectorField": { "type": "dense_vector", "dims": 3, "similarity": "l2_norm", "index": true } } } }"""
+              )
+            ),
+            Executor.execute(ElasticRequest.deleteIndex(firstSearchIndex)).orDie
+          ),
+          test("search for top two results with filters") {
+            checkOnce(genDocumentId, genTestDocument, genDocumentId, genTestDocument, genDocumentId, genTestDocument) {
+              (firstDocumentId, firstDocument, secondDocumentId, secondDocument, thirdDocumentId, thirdDocument) =>
+                for {
+                  _                    <- Executor.execute(ElasticRequest.deleteByQuery(firstSearchIndex, matchAll))
+                  firstDocumentUpdated  = firstDocument.copy(intField = 15, vectorField = List(1, 5, -20))
+                  secondDocumentUpdated = secondDocument.copy(intField = 21, vectorField = List(42, 8, -15))
+                  thirdDocumentUpdated  = thirdDocument.copy(intField = 4, vectorField = List(15, 11, 23))
+                  req1                  = ElasticRequest.create(firstSearchIndex, firstDocumentId, firstDocumentUpdated)
+                  req2                  = ElasticRequest.create(firstSearchIndex, secondDocumentId, secondDocumentUpdated)
+                  req3                  = ElasticRequest.create(firstSearchIndex, thirdDocumentId, thirdDocumentUpdated)
+                  _                    <- Executor.execute(ElasticRequest.bulk(req1, req2, req3).refreshTrue)
+                  query                 = ElasticQuery.kNN(TestDocument.vectorField, 2, 3, Chunk(-5.0, 9.0, -12.0))
+                  filter                = ElasticQuery.range(TestDocument.intField).gt(10)
+                  res <- Executor
+                           .execute(ElasticRequest.knnSearch(firstSearchIndex, query).filter(filter))
+                           .documentAs[TestDocument]
+                } yield (assert(res)(equalTo(Chunk(firstDocumentUpdated, secondDocumentUpdated))))
+            }
+          } @@ around(
+            Executor.execute(
+              ElasticRequest.createIndex(
+                firstSearchIndex,
+                """{ "mappings": { "properties": { "vectorField": { "type": "dense_vector", "dims": 3, "similarity": "l2_norm", "index": true } } } }"""
+              )
+            ),
+            Executor.execute(ElasticRequest.deleteIndex(firstSearchIndex)).orDie
+          )
+        ) @@ shrinks(0),
         suite("searching for documents")(
           test("search for a document using a boosting query") {
             checkOnce(genDocumentId, genTestDocument, genDocumentId, genTestDocument) {

modules/integration/src/test/scala/zio/elasticsearch/IntegrationSpec.scala

@@ -83,14 +83,16 @@ trait IntegrationSpec extends ZIOSpecDefault {
     doubleField     <- Gen.double(100, 2000)
     booleanField    <- Gen.boolean
     geoPointField   <- genGeoPoint
+    vectorField     <- Gen.listOfN(5)(Gen.int(-10, 10))
   } yield TestDocument(
     stringField = stringField,
     dateField = dateField,
     subDocumentList = subDocumentList,
     intField = intField,
     doubleField = doubleField,
     booleanField = booleanField,
-    geoPointField = geoPointField
+    geoPointField = geoPointField,
+    vectorField = vectorField
   )
 
   def genTestSubDocument: Gen[Any, TestSubDocument] = for {

modules/library/src/main/scala/zio/elasticsearch/ElasticQuery.scala

@@ -546,6 +546,46 @@ object ElasticQuery {
   final def ids(value: String, values: String*): IdsQuery[Any] =
     Ids(values = Chunk.fromIterable(value +: values))
 
+  /**
+   * Constructs a type-safe instance of [[zio.elasticsearch.query.KNNQuery]] using the specified parameters.
+   * [[zio.elasticsearch.query.KNNQuery]] is used to perform a k-nearest neighbor (kNN) search and returns the matching
+   * documents.
+   *
+   * @param field
+   *   the type-safe field for which query is specified for
+   * @param k
+   *   number of nearest neighbors to return as top hits (must be less than `numCandidates`)
+   * @param numCandidates
+   *   number of nearest neighbor candidates to consider per shard
+   * @param queryVector
+   *   query vector
+   * @tparam S
+   *   document for which field query is executed
+   * @return
+   *   an instance of [[zio.elasticsearch.query.KNNQuery]] that represents the kNN query to be performed.
+   */
+  final def kNN[S](field: Field[S, _], k: Int, numCandidates: Int, queryVector: Chunk[Double]): KNNQuery[S] =
+    KNN(field = field.toString, k = k, numCandidates = numCandidates, queryVector = queryVector, similarity = None)
+
+  /**
+   * Constructs an instance of [[zio.elasticsearch.query.KNNQuery]] using the specified parameters.
+   * [[zio.elasticsearch.query.KNNQuery]] is used to perform a k-nearest neighbor (kNN) search and returns the matching
+   * documents.
+   *
+   * @param field
+   *   the field for which query is specified for
+   * @param k
+   *   number of nearest neighbors to return as top hits (must be less than `numCandidates`)
+   * @param numCandidates
+   *   number of nearest neighbor candidates to consider per shard
+   * @param queryVector
+   *   query vector
+   * @return
+   *   an instance of [[zio.elasticsearch.query.KNNQuery]] that represents the kNN query to be performed.
+   */
+  final def kNN(field: String, k: Int, numCandidates: Int, queryVector: Chunk[Double]): KNNQuery[Any] =
+    KNN(field = field, k = k, numCandidates = numCandidates, queryVector = queryVector, similarity = None)
+
   /**
    * Constructs an instance of [[zio.elasticsearch.query.MatchAllQuery]] used for matching all documents.
    *

modules/library/src/main/scala/zio/elasticsearch/ElasticRequest.scala

@@ -22,13 +22,14 @@ import zio.elasticsearch.IndexSelector.IndexNameSyntax
 import zio.elasticsearch.aggregation.ElasticAggregation
 import zio.elasticsearch.executor.response.BulkResponse
 import zio.elasticsearch.highlights.Highlights
-import zio.elasticsearch.query.ElasticQuery
 import zio.elasticsearch.query.sort.Sort
+import zio.elasticsearch.query.{ElasticQuery, KNNQuery}
 import zio.elasticsearch.request._
 import zio.elasticsearch.request.options._
 import zio.elasticsearch.result.{
   AggregateResult,
   GetResult,
+  KNNSearchResult,
   SearchAndAggregateResult,
   SearchResult,
   UpdateByQueryResult
@@ -215,6 +216,20 @@ object ElasticRequest {
   final def getById(index: IndexName, id: DocumentId): GetByIdRequest =
     GetById(index = index, id = id, refresh = None, routing = None)
 
+  /**
+   * Constructs an instance of [[KNNRequest]] used for performing a k-nearest neighbour (kNN) search. Given a query
+   * vector, it finds the k closest vectors and returns those documents as search hits.
+   *
+   * @param selectors
+   *   the name of the index or more indices to search in
+   * @param query
+   *   an instance of [[zio.elasticsearch.query.KNNQuery]] to run
+   * @return
+   *   an instance of [[KNNRequest]] that represents k-nearest neighbour (kNN) operation to be performed.
+   */
+  final def knnSearch[I: IndexSelector](selectors: I, query: KNNQuery[_]): KNNRequest =
+    KNN(knn = query, selectors = selectors.toSelector, filter = None, routing = None)
+
   /**
    * Constructs an instance of [[RefreshRequest]] used for refreshing an index with the specified name.
    *
@@ -593,6 +608,40 @@ object ElasticRequest {
       self.copy(routing = Some(value))
   }
 
+  sealed trait KNNRequest extends ElasticRequest[KNNSearchResult] with HasRouting[KNNRequest] {
+
+    /**
+     * Adds an [[zio.elasticsearch.ElasticQuery]] to the [[zio.elasticsearch.ElasticRequest.KNNRequest]] to filter the
+     * documents that can match. If not provided, all documents are allowed to match.
+     *
+     * @param query
+     *   the Elastic query to be added
+     * @return
+     *   an instance of a [[zio.elasticsearch.ElasticRequest.KNNRequest]] that represents the kNN search operation
+     *   enriched with filter query to be performed.
+     */
+    def filter(query: ElasticQuery[_]): KNNRequest
+  }
+
+  private[elasticsearch] final case class KNN(
+    knn: KNNQuery[_],
+    selectors: String,
+    filter: Option[ElasticQuery[_]],
+    routing: Option[Routing]
+  ) extends KNNRequest { self =>
+
+    def filter(query: ElasticQuery[_]): KNNRequest =
+      self.copy(filter = Some(query))
+
+    def routing(value: Routing): KNNRequest =
+      self.copy(routing = Some(value))
+
+    private[elasticsearch] def toJson: Json = {
+      val filterJson: Json = filter.fold(Obj())(f => Obj("filter" -> f.toJson(None)))
+      Obj("knn" -> knn.toJson) merge filterJson
+    }
+  }
+
   sealed trait RefreshRequest extends ElasticRequest[Boolean]
 
   private[elasticsearch] final case class Refresh(selectors: String) extends RefreshRequest
@@ -612,7 +661,7 @@ object ElasticRequest {
      * [[zio.elasticsearch.ElasticRequest.SearchRequest]].
      *
      * @param aggregation
-     *   the elastic aggregation to be added
+     *   the Elastic aggregation to be added
      * @return
      *   an instance of a [[zio.elasticsearch.ElasticRequest.SearchAndAggregateRequest]] that represents search and
      *   aggregate operations to be performed.

modules/library/src/main/scala/zio/elasticsearch/executor/HttpExecutor.scala

@@ -79,6 +79,7 @@ private[elasticsearch] final class HttpExecutor private (esConfig: ElasticConfig
       case r: DeleteIndex        => executeDeleteIndex(r)
       case r: Exists             => executeExists(r)
       case r: GetById            => executeGetById(r)
+      case r: KNN                => executeKnn(r)
       case r: Refresh            => executeRefresh(r)
       case r: Search             => executeSearch(r)
       case r: SearchAndAggregate => executeSearchAndAggregate(r)
@@ -372,6 +373,31 @@ private[elasticsearch] final class HttpExecutor private (esConfig: ElasticConfig
       }
     }
 
+  private def executeKnn(r: KNN): Task[KNNSearchResult] = {
+    val uri = uri"${esConfig.uri}/${r.selectors}/_knn_search".withParams(
+      getQueryParams(Chunk(("routing", r.routing)))
+    )
+
+    sendRequestWithCustomResponse[SearchWithAggregationsResponse](
+      baseRequest
+        .post(uri)
+        .response(asJson[SearchWithAggregationsResponse])
+        .contentType(ApplicationJson)
+        .body(r.toJson)
+    ).flatMap { response =>
+      response.code match {
+        case HttpOk =>
+          response.body.fold(
+            e => ZIO.fail(new ElasticException(s"Exception occurred: ${e.getMessage}")),
+            value =>
+              ZIO.succeed(new KNNSearchResult(itemsFromDocumentsWithHighlights(value.resultsWithHighlightsAndSort)))
+          )
+        case _ =>
+          ZIO.fail(handleFailuresFromCustomResponse(response))
+      }
+    }
+  }
+
   private def executeRefresh(r: Refresh): Task[Boolean] =
     sendRequest(baseRequest.get(uri"${esConfig.uri}/${r.selectors}/$Refresh")).flatMap { response =>
       response.code match {

modules/library/src/main/scala/zio/elasticsearch/query/Queries.scala

@@ -266,6 +266,44 @@ private[elasticsearch] final case class Exists[S](field: String, boost: Option[D
     )
 }
 
+sealed trait KNNQuery[-S] { self =>
+
+  /**
+   * Sets the `similarity` parameter for the [[zio.elasticsearch.query.KNNQuery]]. The `similarity` parameter is the
+   * required minimum similarity for a vector to be considered a match.
+   *
+   * @param value
+   *   a non-negative real number used for the `similarity`
+   * @return
+   *   an instance of [[zio.elasticsearch.query.KNNQuery]] enriched with the `similarity` parameter.
+   */
+  def similarity(value: Double): KNNQuery[S]
+
+  private[elasticsearch] def toJson: Json
+}
+
+private[elasticsearch] final case class KNN[S](
+  field: String,
+  k: Int,
+  numCandidates: Int,
+  queryVector: Chunk[Double],
+  similarity: Option[Double]
+) extends KNNQuery[S] { self =>
+
+  def similarity(value: Double): KNN[S] =
+    self.copy(similarity = Some(value))
+
+  private[elasticsearch] def toJson: Json = {
+    val similarityJson = similarity.fold(Obj())(s => Obj("similarity" -> s.toJson))
+    Obj(
+      "field"          -> field.toJson,
+      "query_vector"   -> Arr(queryVector.map(_.toJson)),
+      "k"              -> k.toJson,
+      "num_candidates" -> numCandidates.toJson
+    ) merge similarityJson
+  }
+}
+
 sealed trait FunctionScoreQuery[S] extends ElasticQuery[S] with HasBoost[FunctionScoreQuery[S]] {
 
   /**

modules/library/src/main/scala/zio/elasticsearch/result/ElasticResult.scala

@@ -106,6 +106,18 @@ final class GetResult private[elasticsearch] (private val doc: Option[Item]) ext
       })
 }
 
+final class KNNSearchResult private[elasticsearch] (private val hits: Chunk[Item]) extends DocumentResult[Chunk] {
+
+  def documentAs[A: Schema]: IO[DecodingException, Chunk[A]] =
+    ZIO.fromEither {
+      ZValidation.validateAll(hits.map(item => ZValidation.fromEither(item.documentAs))).toEitherWith { errors =>
+        DecodingException(s"Could not parse all documents successfully: ${errors.map(_.message).mkString(", ")}")
+      }
+    }
+
+  lazy val items: UIO[Chunk[Item]] = ZIO.succeed(hits)
+}
+
 final class SearchResult private[elasticsearch] (
   private val hits: Chunk[Item],
   private val fullResponse: SearchWithAggregationsResponse