Support kNN filter on nested metadata

Current knn search over nested vectors only supports filtering
on parent's meatadata. This adds support for filtering over
nested metadata.

Closes elastic#106994

docs/reference/query-dsl/knn-query.asciidoc

@@ -240,26 +240,30 @@ to <<nested-knn-search, top level nested kNN search>>:
 
 * kNN search over nested dense_vectors diversifies the top results over
 the top-level document
-* `filter`  over the top-level document metadata is supported and acts as a
-pre-filter
-* `filter` over `nested` field metadata is not supported
+* `filter`  is supported both over the top-level document metadata and `nested`
+field metadata. Filter acts as a pre-filter.
 
-A sample query can look like below:
+A sample query with filter over nested metadata can look like below:
 
 [source,js]
 ----
 {
-  "query" : {
-    "nested" : {
-      "path" : "paragraph",
-        "query" : {
-          "knn": {
-            "query_vector": [
-                0.45,
-                45
-            ],
-            "field": "paragraph.vector",
-            "num_candidates": 2
+  "query": {
+    "nested": {
+      "path": "paragraph",
+      "query": {
+        "knn": {
+          "query_vector": [
+            0.45,
+            45
+          ],
+          "field": "paragraph.vector",
+          "k": 10,
+          "filter": {
+            "match": {
+              "paragraph.language": "EN"
+            }
+          }
         }
       }
     }
@@ -268,6 +272,9 @@ A sample query can look like below:
 ----
 // NOTCONSOLE
 
+The above query only considers vectors with `"paragraph.language": "EN"`
+for scoring parents' documents.
+
 [[knn-query-aggregations]]
 ==== Knn query with aggregations
 `knn` query calculates aggregations on top `k` documents from each shard.

docs/reference/search/search-your-data/knn-search.asciidoc

@@ -677,6 +677,9 @@ PUT passage_vectors
                             "type": "hnsw"
                         }
                     },
+                    "language": {
+                        "type" : "keyword"
+                    },
                     "text": {
                         "type": "text",
                         "index": false
@@ -695,9 +698,9 @@ With the above mapping, we can index multiple passage vectors along with storing
 ----
 POST passage_vectors/_bulk?refresh=true
 { "index": { "_id": "1" } }
-{ "full_text": "first paragraph another paragraph", "creation_time": "2019-05-04", "paragraph": [ { "vector": [ 0.45, 45 ], "text": "first paragraph", "paragraph_id": "1" }, { "vector": [ 0.8, 0.6 ], "text": "another paragraph", "paragraph_id": "2" } ] }
+{ "full_text": "first paragraph another paragraph", "creation_time": "2019-05-04", "paragraph": [ { "vector": [ 0.45, 45 ], "text": "first paragraph", "paragraph_id": "1", "language": "EN" }, { "vector": [ 0.8, 0.6 ], "text": "another paragraph", "paragraph_id": "2", "language": "FR"  } ] }
 { "index": { "_id": "2" } }
-{ "full_text": "number one paragraph number two paragraph", "creation_time": "2020-05-04", "paragraph": [ { "vector": [ 1.2, 4.5 ], "text": "number one paragraph", "paragraph_id": "1" }, { "vector": [ -1, 42 ], "text": "number two paragraph", "paragraph_id": "2" } ] }
+{ "full_text": "number one paragraph number two paragraph", "creation_time": "2020-05-04", "paragraph": [ { "vector": [ 1.2, 4.5 ], "text": "number one paragraph", "paragraph_id": "1", "language": "FR"  }, { "vector": [ -1, 42 ], "text": "number two paragraph", "paragraph_id": "2", "language": "EN"  } ] }
 ----
 //TEST[continued]
 //TEST[s/\.\.\.//]
@@ -776,12 +779,8 @@ scored by their nearest passage vector (e.g. `"paragraph.vector"`).
 ----
 // TESTRESPONSE[s/"took": 4/"took" : "$body.took"/]
 
-What if you wanted to filter by some top-level document metadata? You can do this by adding `filter` to your
-`knn` clause.
-
-
-NOTE: `filter` will always be over the top-level document metadata. This means you cannot filter based on `nested`
-      field metadata.
+What if you wanted to filter by some document metadata? You can do this by adding `filter` to your
+`knn` clause. `filter` can be run based on both: the top-level document metadata and `nested` field metadata.
 
 [source,console]
 ----
@@ -858,6 +857,37 @@ Now we have filtered based on the top level `"creation_time"` and only one docum
 ----
 // TESTRESPONSE[s/"took": 4/"took" : "$body.took"/]
 
+
+Filtering by nested field metadata: `paragraph.language` makes kNN search only consider vectors with this metadata
+for scoring parents' documents:
+
+[source,console]
+----
+POST passage_vectors/_search
+{
+    "fields": [
+        "creation_time",
+        "full_text"
+    ],
+    "_source": false,
+    "knn": {
+        "query_vector": [
+            0.45,
+            45
+        ],
+        "field": "paragraph.vector",
+        "k": 2,
+        "num_candidates": 2,
+        "filter": {
+            "match" : {
+                "paragraph.language" : "EN"
+            }
+        }
+    }
+}
+----
+//TEST[continued]
+
 [discrete]
 [[nested-knn-search-inner-hits]]
 ==== Nested kNN Search with Inner hits

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/100_knn_nested_search.yml

@@ -16,6 +16,8 @@ setup:
               nested:
                 type: nested
                 properties:
+                  language:
+                    type: keyword
                   paragraph_id:
                     type: keyword
                   vector:
@@ -37,8 +39,10 @@ setup:
           nested:
           - paragraph_id: 0
             vector: [230.0, 300.33, -34.8988, 15.555, -200.0]
+            language: EN
           - paragraph_id: 1
             vector: [240.0, 300, -3, 1, -20]
+            language: FR
 
   - do:
       index:
@@ -49,10 +53,13 @@ setup:
           nested:
           - paragraph_id: 0
             vector: [-0.5, 100.0, -13, 14.8, -156.0]
+            language: EN
           - paragraph_id: 2
             vector: [0, 100.0, 0, 14.8, -156.0]
+            language: EN
           - paragraph_id: 3
             vector: [0, 1.0, 0, 1.8, -15.0]
+            language: FR
 
   - do:
       index:
@@ -63,6 +70,7 @@ setup:
           nested:
             - paragraph_id: 0
               vector: [0.5, 111.3, -13.0, 14.8, -156.0]
+              language: FR
 
   - do:
       indices.refresh: {}
@@ -461,3 +469,72 @@ setup:
   - match: {hits.hits.0._id: "2"}
   - length: {hits.hits.0.inner_hits.nested.hits.hits: 1}
   - match: {hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0"}
+
+
+---
+"Test filter on nested fields":
+  - requires:
+      capabilities:
+        - method: POST
+          path: /_search
+          capabilities: [ knn_filter_on_nested_fields ]
+      test_runner_features: ["capabilities", "close_to"]
+      reason: "Capability for filtering on nested fields required"
+
+  - do:
+      search:
+        index: test
+        body:
+          _source: false
+          knn:
+            boost: 2
+            field: nested.vector
+            query_vector: [ -0.5, 90.0, -10, 14.8, -156.0 ]
+            k: 3
+            num_candidates: 10
+            filter: { match: { nested.language: "EN" } }
+            inner_hits: { size: 3, "fields": [ "nested.paragraph_id", "nested.language"], _source: false }
+
+  - match: { hits.total.value: 2 }
+  - match: { hits.hits.0._id: "2" }
+  - match: { hits.hits.0.inner_hits.nested.hits.total.value: 2 }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "EN" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.1.fields.nested.0.paragraph_id.0: "2" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.1.fields.nested.0.language.0: "EN" }
+  - close_to: { hits.hits.0._score: { value: 0.0182, error: 0.0001 } }
+  - close_to: { hits.hits.0.inner_hits.nested.hits.hits.0._score: { value:  0.0182, error: 0.0001 } }
+  - match: { hits.hits.1._id: "1" }
+  - match: { hits.hits.1.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "EN" }
+
+  - do:
+      search:
+        index: test
+        body:
+          _source: false
+          knn:
+            boost: 2
+            field: nested.vector
+            query_vector: [ -0.5, 90.0, -10, 14.8, -156.0 ]
+            k: 3
+            num_candidates: 10
+            filter: { match: { nested.language: "FR" } }
+            inner_hits: { size: 3, "fields": [ "nested.paragraph_id", "nested.language"], _source: false }
+
+  - match: { hits.total.value: 3 }
+  - match: { hits.hits.0._id: "3" }
+  - match: { hits.hits.0.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }
+  - close_to: { hits.hits.0._score: { value: 0.0043, error: 0.0001 } }
+  - close_to: { hits.hits.0.inner_hits.nested.hits.hits.0._score: { value: 0.0043, error: 0.0001 } }
+  - match: { hits.hits.1._id: "2" }
+  - match: { hits.hits.1.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "3" }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }
+  - match: { hits.hits.2._id: "1" }
+  - match: { hits.hits.2.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.2.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "1" }
+  - match: { hits.hits.2.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/search.vectors/130_knn_query_nested_search.yml

@@ -16,6 +16,8 @@ setup:
               nested:
                 type: nested
                 properties:
+                  language:
+                    type: keyword
                   paragraph_id:
                     type: keyword
                   vector:
@@ -38,8 +40,10 @@ setup:
           nested:
           - paragraph_id: 0
             vector: [230.0, 300.33, -34.8988, 15.555, -200.0]
+            language: EN
           - paragraph_id: 1
             vector: [240.0, 300, -3, 1, -20]
+            language: FR
 
   - do:
       index:
@@ -50,10 +54,13 @@ setup:
           nested:
           - paragraph_id: 0
             vector: [-0.5, 100.0, -13, 14.8, -156.0]
+            language: EN
           - paragraph_id: 2
             vector: [0, 100.0, 0, 14.8, -156.0]
+            language: EN
           - paragraph_id: 3
             vector: [0, 1.0, 0, 1.8, -15.0]
+            language: FR
 
   - do:
       index:
@@ -64,6 +71,7 @@ setup:
           nested:
             - paragraph_id: 0
               vector: [0.5, 111.3, -13.0, 14.8, -156.0]
+              language: FR
 
   - do:
       indices.refresh: {}
@@ -406,3 +414,82 @@ setup:
 
   - match: {hits.total.value: 1}
   - match: {hits.hits.0._id: "2"}
+
+
+---
+"Test filter on nested fields":
+  - requires:
+      capabilities:
+        - method: POST
+          path: /_search
+          capabilities: [ knn_filter_on_nested_fields ]
+      test_runner_features: ["capabilities", "close_to"]
+      reason: "Capability for filtering on nested fields required"
+
+  - do:
+      search:
+        index: test
+        body:
+          _source: false
+          query:
+            nested:
+              path: nested
+              query:
+                knn:
+                  boost: 2
+                  field: nested.vector
+                  query_vector: [-0.5, 90.0, -10, 14.8, -156.0]
+                  k: 10
+                  filter:
+                    match:
+                      nested.language: "EN"
+              inner_hits: { size: 3, "fields": [ "nested.paragraph_id", "nested.language"], _source: false }
+
+  - match: {hits.total.value: 2}
+  - match: {hits.hits.0._id: "2"}
+  - match: { hits.hits.0.inner_hits.nested.hits.total.value: 2 }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "EN" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.1.fields.nested.0.paragraph_id.0: "2" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.1.fields.nested.0.language.0: "EN" }
+  - close_to: { hits.hits.0._score: { value: 0.02036, error: 0.0001 } }
+  - close_to: { hits.hits.0.inner_hits.nested.hits.hits.0._score: { value: 0.02036, error: 0.0001 } }
+  - match: {hits.hits.1._id: "1"}
+  - match: { hits.hits.1.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "EN" }
+
+  - do:
+      search:
+        index: test
+        body:
+          _source: false
+          query:
+            nested:
+              path: nested
+              query:
+                knn:
+                  boost: 2
+                  field: nested.vector
+                  query_vector: [ -0.5, 90.0, -10, 14.8, -156.0 ]
+                  k: 10
+                  filter:
+                    match:
+                      nested.language: "FR"
+              inner_hits: { size: 3, "fields": [ "nested.paragraph_id", "nested.language" ], _source: false }
+
+  - match: { hits.total.value: 3 }
+  - match: { hits.hits.0._id: "3" }
+  - match: { hits.hits.0.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "0" }
+  - match: { hits.hits.0.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }
+  - close_to: { hits.hits.0._score: { value: 0.0041, error: 0.0001 } }
+  - close_to: { hits.hits.0.inner_hits.nested.hits.hits.0._score: { value: 0.0041, error: 0.0001 } }
+  - match: { hits.hits.1._id: "2" }
+  - match: { hits.hits.1.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "3" }
+  - match: { hits.hits.1.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }
+  - match: { hits.hits.2._id: "1" }
+  - match: { hits.hits.2.inner_hits.nested.hits.total.value: 1 }
+  - match: { hits.hits.2.inner_hits.nested.hits.hits.0.fields.nested.0.paragraph_id.0: "1" }
+  - match: { hits.hits.2.inner_hits.nested.hits.hits.0.fields.nested.0.language.0: "FR" }

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -231,6 +231,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion CCS_REMOTE_TELEMETRY_STATS = def(8_755_00_0);
     public static final TransportVersion ESQL_CCS_EXECUTION_INFO = def(8_756_00_0);
     public static final TransportVersion REGEX_AND_RANGE_INTERVAL_QUERIES = def(8_757_00_0);
+    public static final TransportVersion TO_CHILD_BLOCK_JOIN_QUERY = def(8_758_00_0);
 
     /*
      * STOP! READ THIS FIRST! No, really,

server/src/main/java/org/elasticsearch/action/search/DfsQueryPhase.java

@@ -157,7 +157,8 @@ ShardSearchRequest rewriteShardSearchRequest(ShardSearchRequest request) {
                 scoreDocs.toArray(Lucene.EMPTY_SCORE_DOCS),
                 source.knnSearch().get(i).getField(),
                 source.knnSearch().get(i).getQueryVector(),
-                source.knnSearch().get(i).getSimilarity()
+                source.knnSearch().get(i).getSimilarity(),
+                source.knnSearch().get(i).getFilterQueries()
             ).boost(source.knnSearch().get(i).boost()).queryName(source.knnSearch().get(i).queryName());
             if (nestedPath != null) {
                 query = new NestedQueryBuilder(nestedPath, query, ScoreMode.Max).innerHit(source.knnSearch().get(i).innerHit());