ROL-2185: Keep comments out of EclipseLink's shared cache

app/src/main/resources/META-INF/persistence.xml

@@ -56,5 +56,13 @@
     <mapping-file>org/apache/roller/planet/pojos/PlanetGroup.orm.xml</mapping-file>
     <mapping-file>org/apache/roller/planet/pojos/Subscription.orm.xml</mapping-file>
     <mapping-file>org/apache/roller/planet/pojos/SubscriptionEntry.orm.xml</mapping-file>
+    <properties>
+      <!-- Background search index operations read comments on their own threads.
+           If one reads a comment just before another thread deletes it, the
+           shared cache can hold the deleted comment after the delete commits,
+           so lookups by id return it (ROL-2185). Comments are always read
+           fresh from the database instead. -->
+      <property name="eclipselink.cache.shared.WeblogEntryComment" value="false"/>
+    </properties>
   </persistence-unit>
 </persistence>

app/src/test/java/org/apache/roller/weblogger/business/jpa/CommentSharedCacheTest.java

@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ *  contributor license agreements.  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.  For additional information regarding
+ * copyright in this work, please see the NOTICE file in the top level
+ * directory of this distribution.
+ */
+
+package org.apache.roller.weblogger.business.jpa;
+
+import java.lang.reflect.Field;
+import jakarta.persistence.Cache;
+
+import org.apache.roller.weblogger.TestUtils;
+import org.apache.roller.weblogger.business.WebloggerFactory;
+import org.apache.roller.weblogger.business.WeblogEntryManager;
+import org.apache.roller.weblogger.pojos.User;
+import org.apache.roller.weblogger.pojos.Weblog;
+import org.apache.roller.weblogger.pojos.WeblogEntry;
+import org.apache.roller.weblogger.pojos.WeblogEntryComment;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Comments stay out of EclipseLink's shared cache. Background search index
+ * operations read comments on their own threads, and a read that overlaps a
+ * delete could otherwise leave the deleted comment in the shared cache, where
+ * lookups by id would still find it (ROL-2185).
+ */
+public class CommentSharedCacheTest {
+
+    private User user;
+    private Weblog weblog;
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        TestUtils.setupWeblogger();
+        user = TestUtils.setupUser("commentcacheuser");
+        weblog = TestUtils.setupWeblog("commentcacheblog", user);
+        TestUtils.endSession(true);
+    }
+
+    @AfterEach
+    public void tearDown() throws Exception {
+        TestUtils.teardownWeblog(weblog.getId());
+        TestUtils.teardownUser(user.getUserName());
+        TestUtils.endSession(true);
+    }
+
+    @Test
+    public void commentsAreNotKeptInTheSharedCache() throws Exception {
+        WeblogEntry entry = TestUtils.setupWeblogEntry("commentcache",
+                TestUtils.getManagedWebsite(weblog), TestUtils.getManagedUser(user));
+        WeblogEntryComment comment = TestUtils.setupComment("cached?", entry);
+        TestUtils.endSession(true);
+
+        WeblogEntryManager mgr = WebloggerFactory.getWeblogger().getWeblogEntryManager();
+        mgr.getWeblogEntry(entry.getId());
+        mgr.getComment(comment.getId());
+        TestUtils.endSession(false);
+
+        Cache cache = strategy().getEntityManager(false).getEntityManagerFactory().getCache();
+        // entries are still cached, so this checks the comment setting, not a disabled cache
+        assertTrue(cache.contains(WeblogEntry.class, entry.getId()));
+        assertFalse(cache.contains(WeblogEntryComment.class, comment.getId()));
+        TestUtils.endSession(false);
+    }
+
+    private static JPAPersistenceStrategy strategy() throws Exception {
+        Field field = JPAWebloggerImpl.class.getDeclaredField("strategy");
+        field.setAccessible(true);
+        return (JPAPersistenceStrategy) field.get(WebloggerFactory.getWeblogger());
+    }
+}