Simplify and document move sibling action (#446)

Author: eugene-andreev

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

@@ -10,7 +10,6 @@
 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;
@@ -22,11 +21,10 @@
 import cds.gen.adminservice.GenreHierarchyMoveSiblingActionContext;
 import cds.gen.adminservice.GenreHierarchy_;
 
-
 @Component
 @ServiceName(AdminService_.CDS_NAME)
 /**
- *  Example of a custom handler for nextSiblingAction
+ * Example of a custom handler for nextSiblingAction
  */
 @Profile("hybrid")
 public class HierarchySiblingActionHandler implements EventHandler {
@@ -40,27 +38,38 @@ public class HierarchySiblingActionHandler implements EventHandler {
     @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();
+        // Get ID of the entry that is being moved
+        String idToMove = (String) CqnAnalyzer.create(event.getModel()).analyze(select).targetKeys()
+                .get(GenreHierarchy_.ID);
+        // Find its' parent
+        String parentId = db.run(Select.from(GenreHierarchy_.class)
+                .columns(c -> c.parent_ID()).where(c -> c.ID().eq(idToMove)))
+                .single(GenreHierarchy.class).getParentId();
+        // Find all children of the parent, which are siblings of the entry being moved
+        List<GenreHierarchy> siblingNodes = db.run(Select.from(GenreHierarchy_.class)
+                .columns(c -> c.ID(), c -> c.siblingRank())
+                .where(c -> c.parent_ID().eq(parentId)))
+                .listOf(GenreHierarchy.class);
+
+        // Shift the sibling ranks to reflect the sort order
+        List<Integer> siblingRanksCopy = siblingNodes.stream().map(ch -> ch.getSiblingRank()).toList();
+
         String nextSiblingId = event.getNextSibling() == null ? null : event.getNextSibling().getId();
-        Optional <GenreHierarchy> nextSibling = siblingNodes.stream().filter(el -> el.getId().equals(nextSiblingId)).findFirst();
+        Optional<GenreHierarchy> nextSibling = siblingNodes.stream().filter(el -> el.getId().equals(nextSiblingId))
+                .findFirst();
 
+        GenreHierarchy nodeToMove = siblingNodes.stream().filter(el -> idToMove.equals(el.getId())).findFirst().get();
         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));
+        // Exchange siblings
+        nextSibling.ifPresentOrElse(n -> siblingNodes.add(siblingNodes.indexOf(n), moved),
+                () -> siblingNodes.addLast(moved));
+        // Apply ranks
+        for (int i = 0; i < siblingRanksCopy.size(); i++) {
+            siblingNodes.get(i).setSiblingRank(siblingRanksCopy.get(i));
         }
 
-        CqnUpdate updateCQN = Update.entity(GenreHierarchy_.class).entries(siblingNodes);
-        db.run(updateCQN);
+        // Update DB
+        db.run(Update.entity(GenreHierarchy_.class).entries(siblingNodes));
         event.setCompleted();
     }
 }