Issue 2577: enable lexical-only findAndRerank (i.e. no-vector/ize one-leg retrieval path)

src/main/java/io/stargate/sgv2/jsonapi/exception/RequestException.java

@@ -55,6 +55,7 @@ public enum Code implements ErrorCode<RequestException> {
 
     INVALID_CREATE_COLLECTION_FIELD,
     INVALID_RERANK_OVERRIDE,
+    MISSING_HYBRID_SORT,
     MISSING_RERANK_QUERY_TEXT,
 
     REQUEST_NOT_JSON,

src/main/java/io/stargate/sgv2/jsonapi/service/resolver/FindAndRerankOperationBuilder.java

@@ -170,6 +170,10 @@ private void checkLimitInBounds(String field, int value, IntConfigWithBounds bou
    */
   private void checkSortSupported() {
 
+    if (!isVectorSort() && !isVectorizeSort() && !isLexicalSort()) {
+      throw RequestException.Code.MISSING_HYBRID_SORT.get();
+    }
+
     if (isVectorSort() || isVectorizeSort()) {
       if (!commandContext.schemaObject().vectorConfig().vectorEnabled()) {
         throw SortException.Code.UNSUPPORTED_VECTOR_SORT_FOR_COLLECTION.get(
@@ -329,12 +333,19 @@ private TaskGroupAndDeferrables<IntermediateCollectionReadTask, CollectionSchema
       taskGroup.add(bm25Read);
     }
 
-    // always a vector or vectorize read
+    // vector or vectorize read (if present)
     var vectorReadAndDeferrables = buildVectorRead(deferredVectorReadAction);
-    taskGroup.add(vectorReadAndDeferrables.task());
+    if (vectorReadAndDeferrables != null) {
+      taskGroup.add(vectorReadAndDeferrables.task());
+    }
+
+    var deferrables =
+        vectorReadAndDeferrables != null
+            ? vectorReadAndDeferrables.deferrables()
+            : List.<Deferrable>of();
 
     // No accumulator, this will be wrapped in an intermediate composite task
-    return new TaskGroupAndDeferrables<>(taskGroup, null, vectorReadAndDeferrables.deferrables());
+    return new TaskGroupAndDeferrables<>(taskGroup, null, deferrables);
   }
 
   private IntermediateCollectionReadTask buildBm25Read(DeferredCommandResultAction deferredAction) {
@@ -369,6 +380,12 @@ private IntermediateCollectionReadTask buildBm25Read(DeferredCommandResultAction
   private TaskAndDeferrables<IntermediateCollectionReadTask, CollectionSchemaObject>
       buildVectorRead(DeferredCommandResultAction deferredAction) {
 
+    if (!isVectorSort() && !isVectorizeSort()) {
+      // we can fake it now, the value will be waiting when the rerank command comes to get it
+      deferredAction.setEmptyMultiDocumentResponse();
+      return null;
+    }
+
     // we can sort with either vectorize OR a BYO vector
     var sortClause = new SortClause(new ArrayList<>());
     DeferredVectorize deferredVectorize = null;
@@ -389,12 +406,10 @@ private IntermediateCollectionReadTask buildBm25Read(DeferredCommandResultAction
               vectorDef.vectorSize(),
               vectorDef.vectorizeDefinition(),
               sortClause);
-    } else if (isVectorSort()) {
+    } else {
       sortClause
           .sortExpressions()
           .add(SortExpression.collectionVectorSort(command.sortClause().vectorSort()));
-    } else {
-      throw new IllegalArgumentException("buildVectorRead() - no vector or vectorize");
     }
 
     // The intermediate task will set the sort when we give it the deferred vectorize

src/main/resources/errors.yaml

@@ -194,6 +194,14 @@ request-errors:
     body: |-
       Unsupported JSON value type for '$hybrid' sub-field: ${errorMessage}.
 
+  - scope:
+    code: MISSING_HYBRID_SORT
+    title: Hybrid sort is missing
+    body: |-
+      The findAndRerank hybrid sort clause must specify at least one sort field: '$vector', '$vectorize', or '$lexical'.
+
+      Resend the command with at least one sort field in '$hybrid'.
+
   - scope:
     code: INVALID_CREATE_COLLECTION_FIELD
     title: Invalid field(s) for createCollection

src/test/java/io/stargate/sgv2/jsonapi/api/v1/FindAndRerankCollectionIntegrationTest.java

@@ -185,11 +185,11 @@ void failOnEmptyRequest() {
 
     givenHeadersPostJsonThen(keyspaceName, collectionName, "{\"findAndRerank\": { } }")
         .body("$", responseIsError())
-        .body("errors[0].errorCode", is(RequestException.Code.MISSING_RERANK_QUERY_TEXT.name()))
+        .body("errors[0].errorCode", is(RequestException.Code.MISSING_HYBRID_SORT.name()))
         .body(
             "errors[0].message",
             containsString(
-                "findAndRerank command is missing the text to use as the query with the reranking"));
+                "The findAndRerank hybrid sort clause must specify at least one sort field"));
   }
 
   private void errorOnNotEnabled(

src/test/java/io/stargate/sgv2/jsonapi/service/resolver/FindAndRerankOperationBuilderTest.java

@@ -242,6 +242,59 @@ void acceptsBoundaryValues() throws Exception {
         .build();
   }
 
+  @Test
+  void bm25OnlyBuildSucceeds() throws Exception {
+    var commandContext = commandContext();
+    var command =
+        command(
+            """
+            {
+              "findAndRerank": {
+                "sort": { "$hybrid": { "$lexical": "text" } },
+                "options": {
+                  "rerankOn": "body",
+                  "rerankQuery": "text"
+                }
+              }
+            }
+            """);
+
+    var operation =
+        new FindAndRerankOperationBuilder(commandContext)
+            .withCommand(command)
+            .withFindCommandResolver(findCommandResolver)
+            .build();
+
+    assertThat(operation).isNotNull();
+  }
+
+  @Test
+  void failsWhenNoSortProvided() throws Exception {
+    var commandContext = commandContext();
+    var command =
+        command(
+            """
+            {
+              "findAndRerank": {
+                "sort": { "$hybrid": {} },
+                "options": {
+                  "rerankOn": "body",
+                  "rerankQuery": "text"
+                }
+              }
+            }
+            """);
+
+    assertThatThrownBy(
+            () ->
+                new FindAndRerankOperationBuilder(commandContext)
+                    .withCommand(command)
+                    .withFindCommandResolver(findCommandResolver)
+                    .build())
+        .isInstanceOf(RequestException.class)
+        .hasFieldOrPropertyWithValue("code", RequestException.Code.MISSING_HYBRID_SORT.name());
+  }
+
   private FindAndRerankCommand command(String json) throws Exception {
     return objectMapper.readValue(json, FindAndRerankCommand.class);
   }