Fix deletion of entities from flattened attributes

cayenne/src/main/java/org/apache/cayenne/access/ObjectStore.java

@@ -1011,6 +1011,18 @@ public Collection<ObjectId> getFlattenedIds(ObjectId objectId) {
                 .getOrDefault(objectId, Collections.emptyMap()).values();
     }
 
+    /**
+     * @since 5.0
+     */
+    public Map<CayennePath,ObjectId> getFlattenedPathIdMap(ObjectId objectId) {
+        if(trackedFlattenedPaths == null) {
+            return Collections.emptyMap();
+        }
+
+        return trackedFlattenedPaths
+                .getOrDefault(objectId, Collections.emptyMap());
+    }
+
     /**
      * Mark that flattened path for object has data row in DB.
      * @since 4.1

cayenne/src/main/java/org/apache/cayenne/access/flush/RootRowOpProcessor.java

@@ -19,7 +19,8 @@
 
 package org.apache.cayenne.access.flush;
 
-import java.util.Collection;
+import java.util.List;
+import java.util.Map;
 
 import org.apache.cayenne.CayenneRuntimeException;
 import org.apache.cayenne.ObjectId;
@@ -29,7 +30,11 @@
 import org.apache.cayenne.access.flush.operation.DeleteDbRowOp;
 import org.apache.cayenne.access.flush.operation.InsertDbRowOp;
 import org.apache.cayenne.access.flush.operation.UpdateDbRowOp;
+import org.apache.cayenne.exp.path.CayennePath;
 import org.apache.cayenne.graph.GraphChangeHandler;
+import org.apache.cayenne.map.DbEntity;
+import org.apache.cayenne.map.DbRelationship;
+import org.apache.cayenne.map.DeleteRule;
 import org.apache.cayenne.map.ObjEntity;
 
 /**
@@ -74,14 +79,38 @@ public Void visitUpdate(UpdateDbRowOp dbRow) {
 
     @Override
     public Void visitDelete(DeleteDbRowOp dbRow) {
-        if (dbRowOpFactory.getDescriptor().getEntity().isReadOnly()) {
+        ObjEntity entity = dbRowOpFactory.getDescriptor().getEntity();
+        if (entity.isReadOnly()) {
             throw new CayenneRuntimeException("Attempt to modify object(s) mapped to a read-only entity: '%s'. " +
-                    "Can't commit changes.", dbRowOpFactory.getDescriptor().getEntity().getName());
+                    "Can't commit changes.", entity.getName());
         }
         diff.apply(deleteHandler);
-        Collection<ObjectId> flattenedIds = dbRowOpFactory.getStore().getFlattenedIds(dbRow.getChangeId());
-        flattenedIds.forEach(id -> dbRowOpFactory.getOrCreate(dbRowOpFactory.getDbEntity(id), id, DbRowOpType.DELETE));
-        if (dbRowOpFactory.getDescriptor().getEntity().getDeclaredLockType() == ObjEntity.LOCK_TYPE_OPTIMISTIC) {
+
+        DbEntity dbSource = entity.getDbEntity();
+        Map<CayennePath,ObjectId> flattenedPathIdMap = dbRowOpFactory.getStore().getFlattenedPathIdMap(dbRow.getChangeId());
+
+        flattenedPathIdMap.entrySet().forEach(entry -> {
+            DbRelationship dbRel = dbSource.getRelationship(entry.getKey().first().toString());
+
+            // Don't delete if the target entity has a toMany relationship with the source entity,
+            // as there may be other records in the source entity with references to it.
+            if (!dbRel.getReverseRelationship().isToMany()) {
+
+                // Get the delete rule for any ObjRelationship matching the flattened
+            	// attributes DbRelationship, defaulting to CASCADE if not found.
+                int deleteRule = entity.getRelationships().stream()
+                        .filter(r -> r.getDbRelationships().equals(List.of(dbRel)))
+                        .map(r -> r.getDeleteRule()).findFirst()
+                        .orElse(DeleteRule.CASCADE);
+
+                if (deleteRule == DeleteRule.CASCADE) {
+                    dbRowOpFactory.getOrCreate(dbRowOpFactory.getDbEntity(entry.getValue()),
+                            entry.getValue(), DbRowOpType.DELETE);
+                }
+            }
+        });
+
+        if (entity.getDeclaredLockType() == ObjEntity.LOCK_TYPE_OPTIMISTIC) {
             dbRowOpFactory.getDescriptor().visitAllProperties(new OptimisticLockQualifierBuilder(dbRow, diff));
         }
         return null;

cayenne/src/test/java/org/apache/cayenne/access/DataContextFlattenedAttributesIT.java

@@ -37,6 +37,7 @@
 import org.apache.cayenne.testdo.testmap.CompoundPainting;
 import org.apache.cayenne.testdo.testmap.CompoundPaintingLongNames;
 import org.apache.cayenne.testdo.testmap.Gallery;
+import org.apache.cayenne.testdo.testmap.PaintingInfo;
 import org.apache.cayenne.unit.di.runtime.CayenneProjects;
 import org.apache.cayenne.unit.di.runtime.RuntimeCase;
 import org.apache.cayenne.unit.di.runtime.UseCayenneRuntime;
@@ -185,7 +186,7 @@ public void testSelectCompound2() throws Exception {
                     "artist2",
                     painting.getArtistName());
             assertEquals(
-                    "CompoundPainting.getArtistName(): " + painting.getGalleryName(),
+                    "CompoundPainting.getGalleryName(): " + painting.getGalleryName(),
                     painting.getToGallery().getGalleryName(),
                     painting.getGalleryName());
         }
@@ -471,14 +472,56 @@ public void testDelete() throws Exception {
 
         Number artistCount = (Number) Cayenne.objectForQuery(context, new EJBQLQuery(
                 "select count(a) from Artist a"));
-        assertEquals(1, artistCount.intValue());
+        assertEquals(2, artistCount.intValue());
         Number paintingCount = (Number) Cayenne.objectForQuery(context, new EJBQLQuery(
                 "select count(a) from Painting a"));
         assertEquals(0, paintingCount.intValue());
 
         Number galleryCount = (Number) Cayenne.objectForQuery(context, new EJBQLQuery(
                 "select count(a) from Gallery a"));
-        assertEquals(0, galleryCount.intValue());
+        assertEquals(1, galleryCount.intValue());
+    }
+
+    @Test
+    public void testDelete2() throws Exception {
+        createTestDataSet();
+
+        long infoCount = ObjectSelect.query(PaintingInfo.class).selectCount(context);
+        assertEquals("PaintingInfo", 8, infoCount);
+
+        List<CompoundPainting> objects = ObjectSelect.query(CompoundPainting.class)
+                .where(CompoundPainting.ARTIST_NAME.eq("artist2"))
+                .select(context);
+
+        // Should have two paintings by the same artist
+        assertEquals("Paintings", 2, objects.size());
+
+        CompoundPainting cp0 = objects.get(0);
+        CompoundPainting cp1 = objects.get(1);
+
+        // Both paintings are at the same gallery
+        assertEquals("Gallery", cp0.getGalleryName(), cp1.getGalleryName());
+
+        context.invalidateObjects(cp0);
+        context.deleteObjects(cp1);
+        context.commitChanges();
+
+        // Delete should only have deleted the painting and its info,
+        // the painting's artist and gallery should not be deleted.
+
+        objects = ObjectSelect.query(CompoundPainting.class)
+                .where(CompoundPainting.ARTIST_NAME.eq("artist2"))
+                .select(runtime.newContext());
+
+        // Should now only have one painting by artist2
+        assertEquals("Painting", 1, objects.size());
+        // and that painting should have a valid gallery
+        assertNotNull("Gallery is null", objects.get(0).getToGallery());
+        assertNotNull("GalleryName is null", objects.get(0).getToGallery().getGalleryName());
+
+        // There should be one less painting info now
+        infoCount = ObjectSelect.query(PaintingInfo.class).selectCount(context);
+        assertEquals("PaintingInfo", 7, infoCount);
     }
 
     @Test