custom handler for nextSiblingAction

Author: etimr

srv/admin-service.cds

@@ -28,7 +28,7 @@ service AdminService @(requires: 'admin') {
   entity GenreHierarchy as projection on my.Genres
     excluding {children} order by siblingRank
     actions {
-      action moveSiblingAction(NextSibling : NextSibling) returns GenreHierarchy;
+      action moveSiblingAction(NextSibling : NextSibling);
     };
 
   extend my.Contents with Hierarchy;

srv/src/main/java/my/bookshop/handlers/HierarchySiblingActionHandler.java

@@ -0,0 +1,66 @@
+package my.bookshop.handlers;
+
+import java.util.List;
+import java.util.Optional;
+
+import org.springframework.context.annotation.Profile;
+import org.springframework.stereotype.Component;
+
+import com.sap.cds.ql.Select;
+import com.sap.cds.ql.Update;
+import com.sap.cds.ql.cqn.CqnAnalyzer;
+import com.sap.cds.ql.cqn.CqnSelect;
+import com.sap.cds.ql.cqn.CqnUpdate;
+
+import com.sap.cds.services.handler.EventHandler;
+import com.sap.cds.services.handler.annotations.On;
+import com.sap.cds.services.handler.annotations.ServiceName;
+import com.sap.cds.services.persistence.PersistenceService;
+
+import cds.gen.adminservice.AdminService_;
+import cds.gen.adminservice.GenreHierarchy;
+import cds.gen.adminservice.GenreHierarchyMoveSiblingActionContext;
+import cds.gen.adminservice.GenreHierarchy_;
+
+
+@Component
+@ServiceName(AdminService_.CDS_NAME)
+/**
+ *  Example of a custom handler for nextSiblingAction
+ */
+@Profile("hybrid")
+public class HierarchySiblingActionHandler implements EventHandler {
+
+    private final PersistenceService db;
+
+    HierarchySiblingActionHandler(PersistenceService db) {
+        this.db = db;
+    }
+
+    @On(entity = GenreHierarchy_.CDS_NAME)
+    void onMoveSiblingAction(GenreHierarchyMoveSiblingActionContext event) {
+        CqnSelect select = event.getCqn();
+        String toMoveId = (String) CqnAnalyzer.create(event.getModel()).analyze(select).targetKeys().get(GenreHierarchy_.ID);
+        CqnSelect parentCQN = Select.from(GenreHierarchy_.class).columns(c -> c.parent_ID()).where(c -> c.ID().eq(toMoveId));
+        GenreHierarchy parentNode = db.run(parentCQN).single(GenreHierarchy.class);
+        CqnSelect childrenCQN = Select.from(GenreHierarchy_.class).columns(c -> c.ID(), c -> c.siblingRank()).where(c -> c.parent_ID().eq(parentNode.getParentId()));
+        List<GenreHierarchy> siblingNodes = db.run(childrenCQN).listOf(GenreHierarchy.class);
+        
+        List<Integer> siblingRanks = siblingNodes.stream().map(ch -> ch.getSiblingRank()).toList();
+        
+        GenreHierarchy nodeToMove = siblingNodes.stream().filter(el -> toMoveId.equals(el.getId())).findFirst().get();
+        String nextSiblingId = event.getNextSibling() == null ? null : event.getNextSibling().getId();
+        Optional <GenreHierarchy> nextSibling = siblingNodes.stream().filter(el -> el.getId().equals(nextSiblingId)).findFirst();
+
+        GenreHierarchy moved = siblingNodes.remove(siblingNodes.indexOf(nodeToMove));
+        nextSibling.ifPresentOrElse(n -> siblingNodes.add(siblingNodes.indexOf(n), moved), () -> siblingNodes.addLast(moved));
+        
+        for (int i=0; i < siblingRanks.size(); i++) {
+            siblingNodes.get(i).setSiblingRank(siblingRanks.get(i));
+        }
+
+        CqnUpdate updateCQN = Update.entity(GenreHierarchy_.class).entries(siblingNodes);
+        db.run(updateCQN);
+        event.setCompleted();
+    }
+}