Add EntityFlattener and use it in the DraftCancelAttachmentsHandler to flatten nested delete requests

Author: lisajulia

cds-feature-attachments/src/main/java/com/sap/cds/feature/attachments/handler/draftservice/DraftCancelAttachmentsHandler.java

@@ -126,13 +126,13 @@ private boolean hasAttachmentAssociations(CdsEntity entity) {
   private List<Attachments> readAttachments(
       DraftCancelEventContext context, CdsStructuredType entity, boolean isActiveEntity) {
     logger.debug(
-        "Reading attachments for entity {} (isActiveEntity={})",
-        entity.getName(),
-        isActiveEntity);
+        "Reading attachments for entity {} (isActiveEntity={})", entity.getName(), isActiveEntity);
     logger.debug("Original CQN: {}", context.getCqn());
+    CqnDelete cqnFlattenedEntity = CQL.copy(context.getCqn(), new EntityFlattener());
     CqnDelete cqnInactiveEntity =
         CQL.copy(
-            context.getCqn(), new ActiveEntityModifier(isActiveEntity, entity.getQualifiedName()));
+            cqnFlattenedEntity,
+            new ActiveEntityModifier(isActiveEntity, entity.getQualifiedName()));
     logger.debug("Modified CQN: {}", cqnInactiveEntity);
     return attachmentsReader.readAttachments(
         context.getModel(), (CdsEntity) entity, cqnInactiveEntity);

cds-feature-attachments/src/main/java/com/sap/cds/feature/attachments/handler/draftservice/EntityFlattener.java

@@ -0,0 +1,62 @@
+/*
+ * © 2024-2025 SAP SE or an SAP affiliate company and cds-feature-attachments contributors.
+ */
+package com.sap.cds.feature.attachments.handler.draftservice;
+
+import com.sap.cds.ql.CQL;
+import com.sap.cds.ql.RefBuilder;
+import com.sap.cds.ql.RefBuilder.RefSegment;
+import com.sap.cds.ql.StructuredTypeRef;
+import com.sap.cds.ql.cqn.CqnPredicate;
+import com.sap.cds.ql.cqn.CqnStructuredTypeRef;
+import com.sap.cds.ql.cqn.Modifier;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Modifier that flattens nested entity references into direct entity references.
+ *
+ * <p>This modifier transforms nested references (e.g., Books → covers) into a single entity
+ * reference (e.g., Books.covers_drafts) while preserving filter conditions from the target segment.
+ */
+class EntityFlattener implements Modifier {
+
+  private static final Logger logger = LoggerFactory.getLogger(EntityFlattener.class);
+
+  EntityFlattener() {}
+
+  @Override
+  public CqnStructuredTypeRef ref(CqnStructuredTypeRef original) {
+
+    RefBuilder<StructuredTypeRef> ref = CQL.copy(original);
+    RefSegment rootSegment = ref.rootSegment();
+
+    // Flatten the query when it's nested, e.g. Books -> Chapters -> Chapters.images
+    if (ref.segments().size() > 1) {
+      logger.debug("Removing nested segments for ref {}", rootSegment);
+    } else {
+      // No nested segments, return as is
+      return original;
+    }
+
+    // Get the filter from the last segment before removing segments
+    RefSegment lastSegment = ref.segments().get(ref.segments().size() - 1);
+    CqnPredicate lastFilter = null;
+    if (lastSegment.filter().isPresent()) {
+      Modifier modifier = new EntityFlattener();
+      lastFilter = CQL.copy(lastSegment.filter().get(), modifier);
+    }
+
+    while (ref.segments().size() > 1) {
+      ref.segments().remove(ref.segments().size() - 1);
+    }
+
+    // Apply the filter to the root segment if there was a filter on the last segment
+    if (lastFilter != null) {
+      rootSegment.filter(lastFilter);
+    }
+
+    // Create a direct reference to the target entity with the modified filter
+    return ref.build();
+  }
+}

cds-feature-attachments/src/test/java/com/sap/cds/feature/attachments/handler/draftservice/EntityFlattenerTest.java

@@ -0,0 +1,50 @@
+/*
+ * © 2024-2025 SAP SE or an SAP affiliate company and cds-feature-attachments contributors.
+ */
+package com.sap.cds.feature.attachments.handler.draftservice;
+
+import static com.sap.cds.services.draft.Drafts.IS_ACTIVE_ENTITY;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.sap.cds.ql.CQL;
+import com.sap.cds.ql.Select;
+import com.sap.cds.ql.cqn.CqnSelect;
+import org.junit.jupiter.api.Test;
+
+public class EntityFlattenerTest {
+
+  @Test
+  void nestedReferenceWithFilterIsFlattened() {
+    // Create a nested reference with a filter on the last segment: AdminService.Books -> covers
+    // (with filter)
+    CqnSelect select =
+        Select.from(
+            "AdminService.Books",
+            c -> c.to("covers").filter(e -> e.get(IS_ACTIVE_ENTITY).eq(false)));
+
+    // The target entity name should be the flattened version
+    var result = CQL.copy(select, new EntityFlattener());
+    // The filter should still be there
+    assertThat(result.toString())
+        .contains("{\"ref\":[\"IsActiveEntity\"]},\"=\",{\"val\":false}]}");
+    // Should contain root entity
+    assertThat(result.toString()).contains("AdminService.Books");
+    // Should not contain the original nested structure
+    assertThat(result.toString()).doesNotContain("\"to\":");
+  }
+
+  @Test
+  void nestedReferenceWithoutFilterIsFlattened() {
+    // Create a nested reference with a filter on the last segment: AdminService.Books -> covers
+    // (with filter)
+    CqnSelect select = Select.from("AdminService.Books", c -> c.to("covers").to("anoter_nesting"));
+
+    // The target entity name should be the flattened version
+    var result = CQL.copy(select, new EntityFlattener());
+    // Should contain root entity
+    assertThat(result.toString()).contains("\"ref\":[\"AdminService.Books\"]");
+    System.out.println(result.toString());
+    // Should not contain the original nested structure
+    assertThat(result.toString()).doesNotContain("\"to\":");
+  }
+}