SOLR-8088: Grouping on a multiValued non-numeric field is rejected up front with a 400 error

changelog/unreleased/SOLR-8088-grouping-multivalued.yml

@@ -0,0 +1,7 @@
+title: Distributed grouping on a multiValued non-numeric field now fails with a clear 400 instead of an IllegalStateException from Lucene docValues.
+type: fixed
+authors:
+  - name: Nick Shanin
+links:
+  - name: SOLR-8088
+    url: https://issues.apache.org/jira/browse/SOLR-8088

solr/core/src/java/org/apache/solr/search/grouping/distributed/command/SearchGroupsFieldCommand.java

@@ -31,6 +31,7 @@
 import org.apache.lucene.search.grouping.ValueSourceGroupSelector;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.mutable.MutableValue;
+import org.apache.solr.common.SolrException;
 import org.apache.solr.schema.FieldType;
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.grouping.Command;
@@ -70,10 +71,25 @@ public SearchGroupsFieldCommand build() {
         throw new IllegalStateException("All fields must be set");
       }
 
+      checkGroupable(field);
       return new SearchGroupsFieldCommand(field, groupSort, topNGroups, includeGroupCount);
     }
   }
 
+  /**
+   * Term based grouping reads single valued docValues; a multiValued field fails deep inside Lucene
+   * ("unexpected docvalues type SORTED_SET"), so reject it with a clear message instead.
+   */
+  static void checkGroupable(SchemaField field) {
+    if (field.getType().getNumberType() == null && field.multiValued()) {
+      throw new SolrException(
+          SolrException.ErrorCode.BAD_REQUEST,
+          "Distributed grouping requires a single valued field, but '"
+              + field.getName()
+              + "' is multiValued; group on a single valued (e.g. copyField) field instead");
+    }
+  }
+
   private final SchemaField field;
   private final Sort groupSort;
   private final int topNGroups;

solr/core/src/java/org/apache/solr/search/grouping/distributed/command/TopGroupsFieldCommand.java

@@ -106,6 +106,7 @@ public TopGroupsFieldCommand build() {
         throw new IllegalStateException("All required fields must be set");
       }
 
+      SearchGroupsFieldCommand.checkGroupable(field);
       return new TopGroupsFieldCommand(
           query,
           field,

solr/core/src/test/org/apache/solr/TestDistributedGrouping.java

@@ -21,6 +21,7 @@
 import java.util.List;
 import org.apache.solr.SolrTestCaseJ4.SuppressPointFields;
 import org.apache.solr.client.solrj.SolrClient;
+import org.apache.solr.client.solrj.request.QueryRequest;
 import org.apache.solr.client.solrj.response.QueryResponse;
 import org.apache.solr.common.SolrDocumentList;
 import org.apache.solr.common.SolrException;
@@ -1727,6 +1728,22 @@ public void testShardRequestFactory() throws Exception {
     }
   }
 
+  @Test
+  public void testMultiValuedGroupFieldIsBadRequest() throws Exception {
+    index("id", "1", "cat", "a");
+    commit();
+
+    ModifiableSolrParams params = new ModifiableSolrParams();
+    params.set("q", "*:*");
+    params.set("group", "true");
+    params.set("group.field", "cat");
+    setDistributedParams(params);
+
+    SolrException e =
+        expectThrows(SolrException.class, () -> new QueryRequest(params).process(clients.get(0)));
+    assertEquals(SolrException.ErrorCode.BAD_REQUEST.code, e.code());
+  }
+
   private QueryResponse simpleQuery(Object... queryParams) throws Exception {
     ModifiableSolrParams params = new ModifiableSolrParams();
     for (int i = 0; i < queryParams.length; i += 2) {

solr/core/src/test/org/apache/solr/search/grouping/distributed/command/SearchGroupsFieldCommandTest.java

@@ -0,0 +1,61 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.search.grouping.distributed.command;
+
+import org.apache.lucene.search.Sort;
+import org.apache.solr.SolrTestCaseJ4;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.schema.SchemaField;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class SearchGroupsFieldCommandTest extends SolrTestCaseJ4 {
+
+  @BeforeClass
+  public static void beforeClass() throws Exception {
+    initCore("solrconfig.xml", "schema.xml");
+  }
+
+  @Test
+  public void testMultiValuedFieldIsRejected() {
+    SchemaField cat = h.getCore().getLatestSchema().getField("cat");
+    assertTrue(cat.multiValued());
+
+    SolrException e =
+        expectThrows(
+            SolrException.class,
+            () ->
+                new SearchGroupsFieldCommand.Builder()
+                    .setField(cat)
+                    .setGroupSort(Sort.RELEVANCE)
+                    .setTopNGroups(10)
+                    .build());
+    assertEquals(SolrException.ErrorCode.BAD_REQUEST.code, e.code());
+    assertTrue(e.getMessage(), e.getMessage().contains("'cat' is multiValued"));
+  }
+
+  @Test
+  public void testSingleValuedFieldIsAccepted() {
+    SchemaField id = h.getCore().getLatestSchema().getField("id");
+    assertFalse(id.multiValued());
+    new SearchGroupsFieldCommand.Builder()
+        .setField(id)
+        .setGroupSort(Sort.RELEVANCE)
+        .setTopNGroups(10)
+        .build();
+  }
+}